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VINEGAR:  ITS  MANUFACTURE  AND  EXAMINATION 


OTHER  WORKS  BY  C.  A.  MITCHELL,  B.A.,  F.I.C.,  F.C.S. 

SECOND  EDITION.     In  Large  8vo.     Cloth.     Pp.  i-xvi  +  266.     Illustrated. 

THE    MANUFACTURE    OF    INK. 

A  Handbook  of  the  Production  and  Properties  of  Printing,  Writing,  and 
Copying  Inks. 

BY  C.  A.  MITCHELL,  B.A.,  F.I.C.,  F.C.S.,  &  T.  C.  IIEPWORTH. 

CONTENTS. — Introduction. — Carbon  and  Carbonaceous  Inks. — Tannin  Materials  for 
Inks. — Nature  of  Inks. — Manufacture  of  Iron  Gall  Inks. — Logwood,  Vanadium,  and 
Aniline  Black  Inks.— Coloured  Writing  Inks.— Examination  o~f  Writing  Inks.— Early 
Methods  of  Manufacture. — Manufacture  of  Varnish  — Preparation  and  Incorporation  of 
the  Pigment. — Coloured  Printing  Inks. — Copying  Inks  — Marking  Inks. — Safety  Inks  and 
Papers. — Sympathetic  Inks. — Inks  for  Special  Purposes  — Engdsh  Patents. — INDEX. 
' '  Thoroughly  well  arranged  .  .  .  and  of  a  genuinely  practical  order." — British  Printer. 


SECOND  EDITION.      In  Large  8vo.      Handsome  Cloth.      With  800  pages 
and  154  Illustrations. 

OILS,    FATS,    BUTTERS,    AND   WAXES: 

THEIR  PREPARATION  AND  PROPERTIES,  AND   MANUFACTURE   THERE- 
FROM OF  CANDLES,    SOAPS,   AND   OTHER  PRODUCTS. 
BY    C.    R.    ALDER    WRIGHT,    D.Sc.,    F.R.S. 

Thoroughly  Revised,  Enlarged,  and  in  Part  Re-written 
BY    C.    AINSWORTH    MITCHELL,    B.A.,    F.I.C.,    F  C.  3. 
ABRIDGED  CONTENTS. — General  Composition  and  Nature  of  Oils,  Butters,  Fats,  and 
Waxes. — Physical  Properties  of  Oils,  Fats,  Waxes,  etc. — Chemical  Properties. — Processes 
for  Extracting,  Rendering,  Refining,  and  Bleaching. — Classification  and  Uses  of  Fixed 
Oils,  Fats,  Waxes,  etc. — Adulteration. — The  Candle  Industry. — The  Soap  Industry. — 
INDEX. 

"Will  be  found  ABSOLUTELY  INDISPENSABLE."—  The  Analyst. 


In    Crown    8vo,    Handsome    Cloth. 

FERMENTS:    AND    THEIR    ACTIONS. 

A   Text-booh  on  the  Chemistry  and  Physics  of  Fermentative  Changes. 

BY  CARL  OPPENHEIMER,    PH.D.,    M.D. 
TRANSLATED  BY  C.  AINSWORTH  MITCHELL,  B.A.,  F.I.C.,  F.C.S. 

CONTENTS. — Introduction. — Definition  of  Ferment. — Chemical  Nature  of  Ferment. — 
influence  of  External  Factors  on  Ferments. — Mode  of  Action. — Physiological  Action. — 
Secretion  of  Ferments. — Ferments  and  the  Vital  Processes. — A.  THE  HYDROLYTIO 
FERMENTS  :  Proteolytic  Ferments. — Trypsin. — Bacteriolytic  and  Hsemolytic. — Proteo- 
lytic  Vegetable  Ferments. — Coagulating  Ferments. — Saccharifying  Ferments. — Animal 
Diastases. — Enzymes  of  the  Disaccharides. — Ferments  which  decompose  Glucosides.— 
Lactic  Acid  Fermentation. — B.  THE  OXIDISING  FERMENTS  :  Alcoholic  Fermentation. — 
Biology  of  do. — The  Oxydases. — Acetic.  Oxalic,  and  similar  Fermentations. — Biblio- 
graphy.— INDEX. 

•'  Such  a  veritable  mu'tnm  in  parvo  has  never  yet  appeared." — Breuns1  Journal. 


Crown  Svo.    Handsome  Cloth.    Pp.  i-xv-f-336.    Fully  Illustrated. 

FLESH    FOODS: 

With  Methods  for  their  Chemical,  Microscopical,  and  Bacteriological  Examination. 

A  Practical  Handbook  for  Medical  Men,  Analysts,  Inspectors  and  others 
BY  C.  AINSWORTH  MITCHELL,  B  A.,  F.I.C.,  F.C  S. 

CONTENTS. — Structure  and  Chemical  Composition  of  Muscular  Fibre. — Structure 
and  Composition  of  Connective  Tissue  and  Blood. — Flesh  of  Different  Animals. — Exami- 
nation of  Flesh. — Animal  Fat. — Preservation  of  Flesh. — Sausages. — Proteids  of  Flesh. — 
Meat  Extracts  and  Flesh  Peptones. — Cooking  of  Flesh. — Poisonous  Flesh. — Animal 
Parasites.— Bacteriological.— Ptomaines.— INDEX. 

"  A  compilation  wnicii  will  be  most  use.ui  lor  uic  cia«  iur  whom  it  is  intended."— Afhenetum. 

LONDON  :  CHARLES  GRIFFIN  &  CO.,  LTD.,  EXETER  STREET,  STRAND. 

PHILADELPHIA  :  J.  B.  LIPPINCOTT  COMPANY. 


VINEGAR: 

ITS  MANUFACTURE  AND  EXAMINATION. 


BY 


C.  AINSWORTH    MITCHELL,  B.A.(OxON.),  F.I.C, 

Chemist  to  Messrs.  Beaufoy  <5r*  Co.,  Manufacturers  of  Vinegar 
for  nearly  200  years. 


With  5  Plates  and  49  other  Illustrations. 


LONDON : 

CHARLES   GRIFFIN   &   COMPANY,   LIMITED, 

PHILADELPHIA  :  J.   B.   LIPPINCOTT  COMPANY. 

1916. 

[A I!  Rights  Reserved.} 


In   recognition   of  numerous  kindnesses  over  a 
period  of  many  years, 

3bts  JSoofc  is  Defctcatefc 

to  the  oldest  firm  in  the  Vinegar  Industry, 
MESSRS.    BEAUFOY   &   COMPANY. 


349278 


PKEFACE. 


CONSIDERING  the  age  of  the  vinegar  industry  in  this 
country,  it  is  strange  that  no  book  has  yet  been  published 
dealing  with  the  subject  from  the  English  point  of  view. 
This  is  partly  due  to  the  fact  that  until  a  comparatively 
recent  date  the  manufacture  of  vinegar  was  regarded 
as  a  mysterious  process,  all  details  of  which  had  to  be 
jealously  guarded,  not  only  from  the  outside  world, 
but  also,  as  far  as  possible,  from  the  workmen  in  the 
factory  itself.  Even  at  the  present  day  this  tradition 
of  secrecy  is  not  quite  dead,  although  the  general  prin- 
ciples of  the  manufacture  are  now  common  property. 

The  information  in  chemical  dictionaries  has  been 
mainly  derived  from  American,  French,  and  German 
books,  which  in  some  respects  are  obsolete,  and  in  any 
case  do  not  embody  the  experience  of  writers  acquainted 
with  the  conditions  of  acetification  in  England. 

At  the  request  of  the  Publishers  I  have  attempted  to 
fill  this  gap,  and  have  tried  to  make  clear  the  scientific 
principles  underlying  each  stage  of  the  manufacture, 
and  to  indicate  the  lines  upon  which  development  of  the 
industry  is  possible. 

In  the  analytical  portion  of  the  book  I  have  assumed 
that  the  reader  will  have  a  general  knowledge  of  analytical 


X  PKEFACE. 

chemistry,  and  have  omitted  details  to  be  found  in  any 
ordinary  text-book.  With  regard  to  the  interpretation 
of  analytical  results,  I  have  laid  stress  on  the  present 
unsatisfactory  state  of  the  law,  and  have  pointed  out 
the  difficulties  which  this  uncertainty  causes  both  to  the 
manufacturer  and  to  the  public  analyst. 

It  gives  me  great  pleasure  to  acknowledge  the  assistance 
I  have  had  from  various  friends  in  writing  the  book,  and 
in  particular  I  would  thank  Messrs.  Beaufoy  &  Co.  and 
Major  Hamilton  Pott  for  allowing  me  to  use  historical 
and  other  material  in  their  possession. 

I  have  also  to  acknowledge  my  indebtedness  to  Messrs. 
Pontifex  &  Co.  for  the  loan  of  blocks  illustrating 
machinery  made  by  them. 

My  best  thanks  are  also  due  to  Miss  M.  B.  Elliott  for 
the  help  she  has  given  me  in  reading  the  proofs. 

C.  A.  M. 

WHITE  COTTAGE, 
THE  COMMON, 
AMERSHAM, 

BUCKINGHAMSHIRE. 


CONTENTS. 


CHAPTER  I. 
HISTORICAL  INTRODUCTION. 

PAGES 

Early  Scientific  Views  :   Vinegar  in  Alchemy  and  latro-Chemistry 
— Domestic  Manufacture — Early  Manufacturing 
Alegar — Vinegar    Manufacturers — Legislation    on    Vinegf 
Proof  Vinegar — The  Acetometer — Trade  Numbers  of  Vinegar,          1-19 

CHAPTER  II. 
THEORIES  OF  ACETIC  FERMENTATION. 

Early  Theories  of  Acetification — Liebig's  Theory — Pasteur's  Views 
— Nageli's  Mechanical  Theory — Later  Enzymic  Theories — 
The  Enzyme  of  Vinegar  Bacteria — Oxidation  and  Reduction 
Processes,  .  .  /  .'  *  .  .  ,  .  20-31 

CHAPTER  III. 
THE  ACETIC  BACTERIA. 

Mycoderma  aceti — Hanson's  Three  Species — Zoogloeal  Condition — 
Involution  Forms — Other  Acetic  Bacteria — Action  of  Light  on 
Acetic  Bacteria— Use  of  Pure  Cultures,  .  .  .  .  32-49 

CHAPTER  IV. 
CHEMICAL  REACTIONS  IN  ACETIFICATION. 

Earlier  Views — Oxidation  in  Acetification — Effects  of  Oxidation — 
Acetaldehyde— Acetal— Ethyl  Acetate— Other  Products- 
Oxidation  of  the  Acetic  Acid — Oxidation  effected  by  Platinum 
Black,  .  .  .  60-56 


Xll  CONTENTS. 

CHAPTER   V. 
ACETIC  ACID. 

PAGES 

Radical  Vinegar — Acetous  Acid — Acetic  Acid  'in  the  Pharma- 
copoeias— Anhydrous  Acetic  Acid — Glacial  Acetic  Acid — 
MANUFACTURE  OF  ACETIC  ACID — from  Verdigris — from  Spirit 
Vinegar — from  the  Distillation  of  Wood — Pyroligneous  Acid — 
from  Acetate  of  Lime — CHEMICAL  PROCESSES  OF  OXIDATION — 
Platinum  Black — Use  of  Ozone — Ozone  in  Acetifiers — Newton's 
Apparatus — Properties  of  Acetic  Acid,  ....  57-76 

CHAPTER   VI. 
PREPARATION  OF  THE  GYLE. 

The  Mash-Tun — Mashing  Machines — Hot-Liquor  Backs — Process 
of  Mashing — Gelatinised  Grain — Addition  of  Sugar — The 
Conversion  Process — Fermentation  of  the  Wort — Storing  the 
Gyle, 77-97 

CHAPTER   VII. 
ACETIFICATION  OF  THE  GYLE. 

APPARATUS  :  The  Slow  Process — Fielding — The  Orleans  Process — 
Claudon's  Apparatus — The  Quick  Process — English  Acetifiers. 
DISTRIBUTION  OF  THE  GYLE  :  The  Sparge — The  Tipping 
Trough — Siphon  Distributors — Aeration  Devices — Wagen- 
mann's  Graduator — Luck's  Acetifier — Singer's  Apparatus — 
Bersch's  Acetifier.  ACETIFICATION  IN  PRACTICE  :  Aeration — 
The  Temperature — Effects  of  Alcohol  and  Acetic  Acid — The 
Group  System — Disturbances  due  to  Mother-of-Vinegar — The 
Vinegar  Eel— The  Vinegar  Mite— The  Vinegar  Fly,  .  .  98-128 

CHAPTER  VIII. 
TREATMENT  OF  THE  CRUDE  VINEGAR. 

Filtration  —  Clarification  —  Action  of  Ferrocyanide  —  Sterilisa- 
tion— Storage — Distillation — Composition  of  the  Residue  in 
the  Still,  ...  ......  129-136 


CONTENTS.  Xlll 

CHAPTER  IX. 
METHODS  OF  EXAMINATION. 

PAGES 

DETERMINATION  OF  ACIDITY — Automatic  Supply  Burette — 
Standardisation  of  Alkali  Solutions — Salleron's  Ac6timetre — 
Otto's  Acetometer — Standards  of  Acidity — Crude  Pyroligneous 
Acid — TOTAL  SOLIDS — Alkalinity  of  the  Ash — MINERAL  ACIDS 
— Detection — Determination — Combined  Sulphuric  Acid — 
Methyl-acetol — FORMIC  ACID — TOTAL  NITROGEN — Nitrogenous 
Compounds — PHOSPHORIC  ACID — INOSITOL  IN  WINE  VINEGAR 
— COLOURING  MATTERS — Measurement  of  Colour  Intensity — 
Lovibond's  Tintometer — Caramel — Cochineal — Archil — MET- 
ALLIC IMPURITIES — Iron — Copper — Lead — Tin — Arsenic — 
Official  Method  of  Testing  for  Arsenic,  .  .  .  .  137-170 

CHAPTER  X. 
CHARACTERISTICS  OF  DIFFERENT  VINEGARS. 

Interpretation  of  Results — CHEMICAL  STANDARDS — Acetic  Strength' 
— Total  Solids — Original  Solids — Nitrogen  and  Phosphoric  Acid 
— Optical  Standard — MALT  VINEGARS — The  Malt  Vinegar 
Question — Composition  of  Malt  Vinegars — Cider  Vinegar — 
Wine  Vinegar — Whey  Vinegar — Fruit  and  Herb  Vinegars — 
Date  Vinegar — Spirit  Vinegars — Essig-sprit — Wood  Vinegar — 
Composition  of  Artificial  Vinegars,  .  .  .  .  .171-191 

APPENDIX  I. — Import  Duties  on  Vinegar  and  Acetic  Acid,    .         .    192-195 
APPENDIX  II. — French  Duties  on  Vinegar,  ....  196 

INDEX,    ....  .    197-201 


LIST  OF  ILLUSTRATIONS. 


Frontispiece. — "  Sending-out  "   Warehouse — Messrs.  Beaufoy  &  Co.'s 
Works  in  1812. 

FIG.  PAGK 

1.  Early  Apparatus  used  for  Distilling  Vinegar,        ....  3 

2.  Excise  List  of  Vinegar  Brewers,  1763, 11 

3.  Obsolete  Excise  Acetometer,      .          .          .          .          .          .          .15 

4.  Pasteur's  Drawing  of  Mycoderma  aceti,       .....  24 

5.  Pasteur's  Experiment  illustrating  the  Absorption  of  Oxygen,         .  26 

6.  Bacterium  aceti  (after  Hansen),           ......  33 

7.  Bacterium  Pasteurianum  (after  Hansen),      .....  33 

8.  Bacterium  Kutzingianum  (after  Hansen),     .....  34 

9.  Bacterium  Pasteurianum — Zooglceal  Formation,  ....  34 

10.  Morphological  Changes  of  B.  Pasteurianum,         .          .          .          .35 

11.  Thread  Formation  of  B.  Pasteurianumt       .         .         .          .          .36 

12.  Transformation  of  B.  Pasteurianum,  ....         .         .          .38 

13.  B.  Pasteurianum — Residue  of  Swollen  Threads,  .         .         .         .37 

14.  B.  Pasteurianum — Conversion  of  Threads  into  Chains  of  Short  Rods, 

to  face  page  38 

15.  Filaments  of  B.  aceti,       .         .         .  .         .         .         .39 

16.  B.  aceti — Unusual  Forms,          .  "  .         .         .         .          .40 

17.  Apparatus  for  Distillation  of  Radical  Vinegar,     .         .         .         .       63 

18.  Newton's  Patent  Process, .          .       71 

19.  Obsolete  Mash-Tun  and  Copper, 78 

20.-  Section  of  Mash- Tun, 79 

21.  The  Sparge, 80 

22.  Section  of  External  Mashing  Machine,         .          .          .          .          .81 

23.  Mash-Tun  with  Steel's  Mashing  Machine,    .      "   .          .          .          .       84 

24.  Underback  and  Refrigerator,  A.D.  1812, 90 

25.  Vertical  Refrigerator, 92 

26.  Exterior  of  Fermenting  Tuns,    .          .          .          .          .to  face  page  93 

27.  Horizontal  Refrigerator,  ........       93 

28.  Fermenting  Tun  with  Cooling  Coil  and  Parachute,       ...       94 

29.  Old  Store  Vats, 96 

30.  Vinegar  Field— Filling  the  Casks, 99 

31.  Vinegar  Field — Drawing-off, 100 


XVI  LIST   OF   ILLUSTRATIONS. 

FIG.  PAGK 

32.  Manufacture  of  Wine  Vinegar.     Orleans  Process,          .          .          .     102 

33.  Claudon's  Acetifying  Apparatus,        ......     104 

34.  Section  of  a  Modern  Acetifier  with  Basket  Work,          .         .         .     107 

35.  Sparge  of  an  Acetifier  (Bronner),         ......     108 

36.  The  Tipping  Trough  (Bronner), 109 

37.  Combined  Siphon  and  Sparge, 110 

38.  Diagram  showing  Aeration  of  an  Acetifier,  .         .         .         .111 

39.  Aeration  Device,      .          .          . 112 

40.  Aeration  Tubes, 112 

41.  Wagenmann's  Graduator,  .          .          .          .          .          .          .113 

42.  Singer's  Acetifier, 115 

43.  Bersch's  Acetifier, 115 

44.  Vinegar  Eels  (Pasteur), 123 

45.  Vinegar  Eel,  highly  magnified  (Pasteur), 124 

46.  Vinegar  Mite, 127 

47.  Vinegar  Mite, 127 

48.  The  Rape  Shed, to  face  page  129 

49.  Diagram  of  Sterilising  Apparatus,      .          .          .          .          .          .134 

50.  Vinegar  Still, to  face  page  135 

51.  Salleron's  Acetimetre,       ........     138 

52.  Lovibond's  Tintometer, .159 

53.  Arsenic  Apparatus,  .         .         .         .         .         .         .         .167 


VINEGAE: 

ITS    MANUFACTURE    AND    EXAMINATION. 


CHAPTER  I. 
HISTORICAL   INTRODUCTION. 

Early  Scientific  Views  :  Vinegar  in  Alchemy  and  latro-Chemistry — Domestic 
Manufacture — Early  Manufacturing  Processes — Alegar — Vinegar  Manu- 
facturers— Legislation  on  Vinegar — Proof  Vinegar — The  Acetometer — 
Trade  Numbers  of  Vinegar. 

Vinegar  in  Alchemy  and  Early  Chemistry. — Passing  over 
various  allusions  in  the  Classics  to  Acetum,  and  the  fable 
of  its  use  by  Hannibal  to  dissolve  the  Alps,  we  find  that 
vinegar  had  its  recognised  place  among  the  products 

of  the  alchemist,  and  was  indicated  by  the  symbols  h-L 
and  }£ ,  while  for  distilled  vinegar  the  characters  >$p  and 
^8J£  were  used.  These  symbols  were  retained  after  the 
transition  of  alchymy  into  what  has  been  termed  "  iatro- 
chymistry,"  from  its  being  mainly  concerned  with  the 
action  of  different  bodies  upon  the  human  system.  The 
doctrines  of  the  alchemists  were  discarded  but  slowly, 
and  we  find  that  even  at  the  beginning  of  the  eighteenth 
century  all  natural  things  were  held  to  consist  of  the 
five  principles — Spirit,  Oil,  and  Salt  (which  were  active), 

and  Water  and  Earth  (which  were  passive). 

1 


2       VINEGAR  !    ITS    MANUFACTURE    AND    EXAMINATION. 

According  to  Lemery,*  there  were  three  sorts  of  liquors 
known  as  Spirit ;  the  Spirit  of  Animals,  the  Burning 
Spirit  of  Vegetables,  and  the  Acid  Spirit.  The  first  was 
typified  by  Spirit  of  Hartshorn,  the  second  by  Spirit  of 
Wine,  while  the  last,  as  "  the  Spirit  of  Vinegar,  Tartar, 
and  Vitriol,  is  an  Acid  Essential  Salt,  dissolved  and  put 
in  fusion  by  the  fire,  as  I  shall  prove  when  I  speak  of 
Vinegar."  f 

In  discussing  the  nature  of  vinegar,  Lemery  remarks  :— 
"  Wines  like  other  Liquors  that  use  to  ferment  do  grow 
sowr  by  the  Dissolution  of  their  Tartar  in  a  second  fer- 
mentation. This  Dissolution  is  commonly  made,  when 
upon  the  Wines  going  to  decay,  some  of  the  more  subtle 
Spirits  are  lost ;  for  the  Tartar  taking  their  Place,  fixes 
the  rest  of  the  Spirits  which  remain  in  the  Wine,  so  that 
they  can  act  no  longer.  This  Fixation  is  the  Cause  that 
when  the  Wine  turns  sowr,  very  little  quantity  of  it  is 
diminished,  and  very  little  Tartar  is  found  in  the  Vessels 
wherein  Vinegar  is  made. 

"  To  the  End  that  Wine  may  quickly  sowr,  you  must 
set  the  Vessel  that  contains  it  in  some  hot  Place,  and  mix 
the  Lees  from  Time  to  Time  ;  for  this  Tartar  will  easily 
dissolve  when  Heat  comes  to  act  upon  it."  .  .  .  "  The 
Acids  (in  Vinegar)  continue  a  long  Time  ;  but  being 
moved  and  continually  agitated  by  the  Sulphurs  which 
intangled  them,  they  at  last  evaporate  into  the  Air ; 
and  so  the  strongest  Vinegar  by  length  of  Time  becomes 
almost  insipid." 

The  following  passage  is  of  interest,  since  it  throws 

*  A  Course  of  Chymistry  (4th  English  edition  from  llth  French  edition), 
1720,  p.  6. 
t/6id.,  p.  404. 


HISTORICAL   INTRODUCTION.  3 

light  upon  the  term  "  radical  "  vinegar,  which  survived 
into  the  last  century,*  and  also  shows  that  a  concentrated 
acetic  acid  was  prepared  from  distilled  vinegar  by  neutral- 
isation, concentration,  and  redistillation,  as  far  back  as 
the  seventeenth  century  : — "  Some  having  dried  and 
calcined  the  sweet  Extract  that  remains  at  the  bottom 
of  the  Cucurbit,  after  the  Distillation  of  Vinegar,  and 
having  by  Solution,  Filtration,  and  Coagulation,  separated 
from  it  an  Alkali  fixt  Salt,  much  like  to  that  which  is 


€.  A  portable  furnace  for  distilling 

with  a  fire  of  sand. 

/.  The  ash-room  and  its  door. 
g.  hearth  and  its  door. 

h.  cucurbit. 

*.  head. 

k.  receiver. 

I.  cucurbit  apart. 

m.  head  apart. 


Fig.  1. — Early  Apparatus  for  Distilling  Vinegar. 

drawn  from  Tartar,  they  mix  it  with  Spirit  of  Vinegar, 
and  distil  and  cohobate  it  divers  Times,  until,  say  they, 
the  Spirit  has  carried  off  all  the  Salt,  and  then  will  needs 
have  it  called  Spirit  of  Vinegar  Alkalized,  or  Radical 
Spirit  of  Vinegar  ;  and  they  affirm  that  this  being  much 
more  pure  and  entirely  united  with  its  proper  Salt,  is 
much  the  more  powerful  in  dissolving  Metals." 

In  the  directions  given  by  Lemery  for  the  distillation 

*  See  the  Act  of  George  III.  of  1818,  p.  12. 


4       VINEGAR  :    ITS   MANUFACTURE   AND   EXAMINATION. 

of  vinegar,  the  liquid  is  first  evaporated  in  an  earthenware 
basin  on  a  hot- water  bath,  until  a  sixth  part,  "  which  is 
the  plegmatic  Part,"  is  expelled.  The  remainder  is  then 
"  poured  into  a  glass  or  earthenware  Cucurbit  and  dis- 
tilled in  a  strong  Sand-heat,  until  there  remains  at  Bottom 
nothing  but  a  Substance  like  Honey/' 

"  This  Spirit  of  Vinegar,"  he  adds,  "  is  mixed  in 
Cordial  Potions  to  resist  Putrefaction.  It  is  mixed  with 
Water,  and  this  Oxycrate  is  used  to  stop  Hemorrhagies 
taken  inwardly,  and  to  asswage  Inflammations  applied 
outwardly. 

"  Neither  Vinegar,  nor  any  other  Acids  are  proper  for 
melancholy  Persons,  because  they  mix  the  Humoures  too 
much  :  They  also  turn  those  who  take  much  of  them 
lean  ;  for  they  give  too  great  Consistency  to  the  Blood, 
and  do  hinder  the  Chyle  from  distributing  itself  sufficiently 
through  the  Body  to  give  Nourishment." 

Domestic  Manufacture. — Long  before  any  vinegar  maker 
was  established  in  this  country  wine  vinegar  appears  to 
have  been  imported  from  France.  In  that  strange 
collection  of  domestic  recipes  handed  down  from  genera- 
tion to  generation  in  the  Fairfax  family,  and  published 
in  facsimile  by  Weddell,*  there  is  one  relating  to  the 
preparation  of  "  Sirrupp  of  Viniger  "  in  handwriting  which 
appears  to  belong  to  the  time  of  Queen  Elizabeth.  In 
this  recipe  the  principal  constituent  is  "  white  wine 
viniger,"  and  as  no  directions  are  given  for  making  it, 
such  as  those  for  the  brewing  of  beer  and  cowslip  wine, 
the  making  of  simples  for  warding  off  the  plague  and 
curing  the  bite  of  a  mad  dog,  or  the  preparation  of 
baths  for  melancholy,  it  seems  fair  to  infer  that  vinegar 

*  Arcana  Fairfaxiana,  1890, 


HISTORICAL   INTRODUCTION.  5 

was  not  made  in  that  household  at  all  events.  Not 
until  the  eighteenth  century  (judging  by  the  writing) 
do  we  find  an  entry  in  the  index  relating  to  the 
making  of  vinegar,  and  the  recipe  corresponding  to 
this  is  not  to  be  found  in  the  body  of  the  manu- 
script. 

The  process  of  brewing  home-made  vinegar  was  pro- 
bably very  similar  to  that  described  by  Mackenzie,* 
in  the  following  words  : — 

"  To  every  gallon  of  water  put  a  Ib.  of  coarse  Lisbon 
sugar ;  let  the  mixture  be  boiled  and  skimmed  as  long 
as  any  scum  arises.  Then  let  it  be  poured  into  proper 
vessels  ;  and  when  it  is  as  cool  as  beer,  when  worked, 
let  a  warm  toast  rubbed  over  with  yeast  be  put  into  it. 
Let  it  work  about  twenty-four  hours,  and  then  put  it 
into  an  iron  hooped  cask,  fixed  either  near  a  constant 
fire,  or  where  the  summer  sun  shines  the  greater  part 
of  the  day  ;  in  this  situation  it  should  not  be  closely 
stopped  up  ;  but  a  tile  or  something  similar  should  be 
laid  on  the  bung  hole,  to  keep  out  the  dust  and  insects. 
At  the  end  of  about  three  months  (sometimes  less)  it 
will  be  clear  and  fit  for  use,  and  may  be  bottled  off.  The 
longer  it  is  kept  after  it  is  bottled,  the  better  it  will  be. 
If  the  bottle  containing  the  liquor  is  to  be  exposed  to 
the  sun's  heat,  the  best  time  to  begin  making  it  is  in  the 
month  of  April." 

Early  Manufacturing  Processes. — The  earliest  descrip- 
tion of  a  process  of  making  vinegar  appears  to  be  that 
published  in  1670  in  the  Transactions  of  the  Royal  Society 
under  the  heading  :  "  The  Way  of  Making  Vinegar  in 
Prance :  Communicated  to  the  Publisher  by  an  In- 

*  One  Thousand  Processes  of  Manufacture,  1828. 


6        VINEGAR  :    ITS    MANUFACTURE    AND    EXAMINATION. 

genious  Physician  of  that  Nation,  living  at  a  Place  where 
much  of  it  is  Made."  * 

Since  this  account  throws  light  upon  the  origin  of 
terms  used  to  this  day  in  the  English  vinegar  industry, 
and  disposes  of  the  claim  that  Boerhave  originated 
the  process  here  described,  it  deserves  quotation  at 
length  : — 

"  They  take  two  great  Casks,  within  each  of  which 
they  put  at  the  bottom  a  Trevet,  which  must  be  one  foot 
high  and  as  large,  as  the  largness  of  the  Cask  permits. 
Upon  this  Trevet  they  put  Vine  twiggs,  whereon  they 
lay  a  substance  called  Rape,  with  which  they  fill  both 
vessels  within  half  a  foot  from  the  top.  This  Rape  is 
nothing  else  but  the  wood  or  stalks  of  the  Clusters  of 
Grapes.  The  Trevet  and  the  Vine  branches  are  put  at 
the  bottom  of  the  Casks,  only  to  keep  the  Rape  from 
setting  at  the  bottom.  It  is  this  Rape  which  alone  heats 
and  sowrs  the  Wine.  The  two  Vessels  being  almost 
quite  filled  with  the  Rape,  one  of  them  is  filled  up  with 
Wine,  and  the  other  only  half  full  for  the  time  ;  and 
every  day  they  draw  by  a  Cock  half  the  Wine  that  is 
in  the  full  vessel,  therewith  quite  to  fill  up  the  other, 
that  is  but  half  full ;  observing  enterchangeable  turns  of 
filling  and  unfilling  the  vessels.  Ordinarily  at  the  end 
of  two  or  three  days  the  half  filled  vessel  begins  to  heat, 
and  this  heat  augments  for  several  dayes  successively, 
continuing  to  do  so  till  the  Vinegar  is  perfectly  made, 
and  the  workmen  know  that  the  Vinegar  is  made  by  the 
ceasing  of  the  heat.  In  summer  it  is  a  work  of  fifteen 
dayes ;  in  winter  it  proceeds  more  slowly,  and  that 
according  to  the  degree  of  Cold  weather.  The  full  vessel 

*  Phil.  Trans.  Roy.  Soc.,  1670,  vol.  v.,  p.  2002. 


HISTORICAL   INTRODUCTION.  7 

is  quite  open  at  the  top,  but  a  wooden  cover  is  put  on 
the  vessel  that  is  but  half  full.  . 

'  The  Wine  in  changing,  leaves  a  certain  grease,  which 
sticks  partly  to  the  sides  of  the  Cask  (and  that  they  take 
care  to  do  clean  away),  partly  to  the  Rape,  so  that  if 
they  cleanse  not  the  Rape  from  it  almost  every  year 
once,  the  Wine  turns  into  a  whitish  liquor,  which  is 
neither  Wine  nor  Vinegar.  In  the  Casks  which  have 
never  served  for  this  purpose  before  the  Vinegar  is 
made  more  slowly  than  in  such  that  have  been  used 
already. 

"  There  is  no  other  way  of  keeping  the  Rape  that 
hath  once  served  already  than  to  drown  it ;  that  is  to 
say,  to  fill  the  vessel  wherein  it  is  with  Wine  or  Vinegar/' 

The  account  given  by  Boerhave  *  of  the  French  method 
of  manufacturing  vinegar  is  substantially  the  same  as 
this  version  of  1670,  and  there  seems  to  be  little  doubt 
but  that  many  English  manufacturers  derived  their 
information  from  one  or  other  of  these  sources. 

Alegar. — The  English  being  a  beer-drinking  nation, 
it  was  to  be  expected  that  the  development  of  the  vinegar 
industry  in  this  country  should  have  come  by  way  of 
beer  rather  than  of  wine.  By  analogy  the  product 
derived  from  beer  became  known  as  "  alegar,"  which 
stood  in  the  same  relation  to  ale  as  vinegar  to  wine. 

Boorde  f  in  the  year  1542  refers  to  both  products  in 
his  "  dyetary,"  where  he  speaks  of  "  Soure  and  Tarte 
Thynges  as  Venegre  and  Aleger." 

The  distinction  between  the  two  products  was  pointed 

*  A  New  Method  of  Chemistry  by  Boerhave.  English  translation  by 
Peter  Shaw,  1753,  vol.  ii.,  p.  129. 

•[First  Boke  of  Introduction  of  Knowledge  (edn.  of  1870),  vol.  xxxiv.,  p.  296. 


8        VINEGAR  :    ITS    MANUFACTURE   AND    EXAMINATION. 

out  by  Cogan  *  in  1586,  in  a  passage  upon  the  making 
of  vinegar,  where  he  remarks  : — "  Some  make  it  of  Ale 
onely  .  .  .  but  that  is  rather  Aliger  than  Viniger." 

The  term  "  alegar  "  is  still  to  be  found  in  glossaries 
of  local  words,  but  is  probably  now  practically  as  obsolete 
as  is  the  old  home-made  product  obtained  by  adding  a 
"  vinegar  plant  "  to  sour  beer. 

The  vinegar  manufacturer  evolved  out  of  the  brewer  ; 
for  the  production  of  vinegar  was  the  obvious  way  of  dis- 
posing of  sour  beer  whether  in  the  household  or  the  brewery. 

It  is  probable  that  the  earliest  English  products  were 
nothing  more  than  ale  partially  converted  into  vinegar 
by  long  exposure  to  the  air.  Subsequently  the  French 
methods  of  manufacture  were  adopted  and  "  wash  "  was 
specifically  brewed  for  the  purpose. 

Vinegar  Manufacturers.  —  In  the  Revenue  Act  of 
Charles  II.  (1673),  the  vinegar  thus  produced  as  a  waste 
product  in  the  "  common  breweries "  was  termed 
"  Vinegar-Beer/'  and  had  to  pay  a  duty  of  sixpence  per 
barrel  (as  against  Is.  3d.  duty  upon  six-shillings'  beer). 

The  date  of  the  establishment  of  the  first  vinegar 
factory  as  distinct  from  the  "  common  brew-house " 
is  uncertain,  but  there  was  undoubtedly  a  "  vinegar 
yard"  in  Castle  Street,  South wark,  as  far  back  as  1641.f 
This  yard  belonged  to  a  man  named  Rush,  "  in  whose 
family  it  remained  a  considerable  and  improving  manu- 
factory until  the  year  1790,  when  it  came  into  the  hands 
of  the  present  proprietors."  J 

*  Cogan,  Haven  Health. 

-^History  and  Antiquities  in  the  Parish  of  St.  Saviour,  Southwark,  1795. 

£  Messrs.  Pott  &  Co.,  who  already  had  a  vinegar  yard  in  the  same 
parish,  established  in  1720.  Early  in  the  present  century  the  firm 
became  amalgamated  with  Messrs.  Beaufoy  &  Co. 


HISTORICAL   INTRODUCTION.  9 

The  only  name  in  the  Excise  list  of  vinegar  makers 
for  1764,  which  is  still  connected  with  the  industry,  is 
that  of  Beaufoy. 

Early  in  the  eighteenth  century  Mark  Beaufoy,  a 
member  of  the  Society  of  Friends,  established  vinegar 
works  on  the  site  of  the  old  Cuper's  Gardens  on  the 
Surrey  side  of  Waterloo  Bridge,  and  within  a  few  years 
they  had  become  the  third  in  importance  in  London. 

Pennant,*  writing  in  1792,  makes  the  following  allusion 
to  these  works  in  his  description  of  London  : — "  There  is 
a  magnificence  of  business  in  this  ocean  of  sweets  and 
sours,  that  cannot  fail  exciting  the  greatest  admiration, 
whether  we  consider  the  number  of  vessels  or  their 
size.  The  boasted  tun  of  Heidelberg  does  not  surpass 
these.  On  first  entering  the  yard  two  rise  before  you, 
covered  at  the  top  with  a  thatched  dome  ;  between  them 
is  a  circular  turret  including  a  winding  staircase,  which 
brings  you  to  their  summits  above  twenty-four  feet  in 
diameter.  One  of  these  conservatories  is  full  of  sweet 
wine,  and  contains  fifty-eight  thousand  one  hundred  and 
nine  gallons  of  Winchester  measure  ;  its  superb  associate 
is  full  of  vinegar  to  the  amount  of  fifty-six  thousand  seven 
hundred  and  ninety-nine  gallons/' 

In  1812  the  ground  occupied  by  these  works  was  re- 
quired for  the  southern  approach  to  Waterloo  Bridge, 
and  the  manufacture  was  transferred  to  its  present  site 
in  South  Lambeth. 

A  Report  of  an  Excise  Commission  which  preceded 
the  alteration  of  the  method  of  collecting  the  duty  upon 
vinegar  showed  that  up  to  the  year  1834  there  were 
seventy-seven  thousand  dealers  in  vinegar  in  Great 

*  London,  3rd  edition,  p.  34. 


10     VINEGAR  I    ITS   MANUFACTURE   AND    EXAMINATION. 

Britain,  every  one  of  whom  received  twelve  visits  a  year 
from  the  Excise  officers.  In  this  report  it  was  also  stated 
that  about  three  million  gallons  of  vinegar  were  brewed 
in  Great  Britain  and  Ireland,  for  more  than  half  of  which 
five  firms  in  London  were  responsible. 

In  the  year  1844  there  were  forty-four  vinegar  makers 
(excluding  manufacturers  of  acetic  acid),  and  they 
produced  in  that  year  2,828,043  gallons  of  proof  vinegar, 
upon  which  a  duty  of  £24,745  7s.  6d.  was  paid.  In  the 
following  year  there  were  65,  but  by  the  year  1860  the 
number  of  vinegar  makers  had  fallen  again  to  about 
50,  and  they  still  produced  about  3,000,000  gallons 
annually.* 

Considerable  light  is  thrown  upon  the  development 
of  vinegar  making  in  this  country  by  a  study  of  the 
successive  Acts  of  Parliament. 

Legislation  upon  Vinegar. — Although  the  legislation  in 
connection  with  vinegar  has  been  mainly  concerned 
with  the  purposes  of  revenue,  it  yet  at  the  same  time 
gives  many  interesting  details  of  the  industry.  In  the 
year  1673,  an  Act  of  Parliament  was  passed  (XII. 
Car.  II.  Cap.  24)  imposing  a  duty  of  6d.  per  gallon  for 
every  Barrel  of  Beer  commonly  called  Vinegar-Beer 
brewed  by  any  common  Brewer  in  any  common  Brew- 
House,  the  work  of  inspection  to  be  carried  out  by  the 
"  gagers "  of  beer,  metheglyn,  etc.  Apparently  the 
revenue  suffered  from  the  evading  of  this  duty,  for  in 
the  year  1696  (VII.  and  VIII.  Wm.  III.  C.  30)  a  penalty 
of  forty  shillings  was  imposed  for  every  barrel  of  vinegar 
concealed  from  the  gaugers,  or  sent  out  of  the  works 
without  due  notice  to  the  Excise  officers. 

*  Muspratt,  Dictionary  of  Chemistry,  1860,  p.  36. 


HISTORICAL   INTRODUCTION. 


11 


In  the  following  reign,  by  an  Act  passed  in  1710  (VIII. 
Anna,  C.   7),  the  duty  upon  vinegar  was  increased  to 


Fig.  2. — Facsimile  of  Excise  List  of  Vinegar  Brewers,  1763. 

9d.  per  barrel,  and  remained  at  that  rate  throughout 
the  wrhole  of  the  following  century. 


12     VINEGAR  :    ITS   MANUFACTURE   AND   EXAMINATION. 

By  the  Act  of  VI.  Geo.  III.  C.  14,  it  was  enacted  that 
cider  and  perry  that  had  turned  sour  and  become  unfit 
for  sale  were  to  pay  duty  as  vinegar;  while  in  1796 
(XXXVI.  Geo.  III.  C.  72)  vinegar-makers  were  not  allowed 
to  have  a  distillery  upon  the  same  premises.  They  were 
also,  before  obtaining  a  licence,  obliged  to  declare  whether 
they  intended  to  make  vinegar  from  malt  or  corn,  or  from 
molasses  or  sugar. 

In  1818  (LVIII.  Geo.  III.  C.  65)  the  old  duties  were 
repealed,  and  a  duty  of  4d.  per  gallon  levied  upon  vinegar, 
vinegar-beer,  alegar,  radical  vinegar,  verjuice,  acetous 
acid,  acetic  acid,  pyroligneous  acid,  and  liquors  intended 
for  vinegar  made  in  England  and  Ireland,  and  of  Is.  per 
gallon  upon  imported  vinegar  and  acetic  acid,  with  a 
drawback  of  4d.  per  gallon  for  exported  products  upon 
which  the  duty  had  been  paid. 

To  prevent  the  introduction  or  sale  of  strong  acetic 
acid  upon  which  only  the  duty  for  "  common  vinegar  " 
had  been  paid,  it  was  enacted  that  "  all  such  liquors 
shall  be  tried  with  such  acetometer  as  may  be  devised 
by  the  Commissioners  of  Excise.  If  found  above  proof 
a  proportional  charge  was  to  be  made  for  the  excess/' 
"  Proof  "  vinegar  was  defined  in  this  Act  as  that  con- 
taining "  such  strength  of  Acetous  Acid  that  100  parts 
of  the  Liquor  by  Weight  shall  saturate  or  neutralize 
14J  parts  by  weight  of  crystallized  subcarbonate  of 
soda."  * 

No  foreign  acid  was  to  be  added  to  vinegar  except 
sulphuric  acid  in  a  proportion  not  exceeding  one 
thousandth  part  by  weight  (Sec.  25). 

Moreover,   no   person   was   allowed   to   make   vinegar 

*  This  corresponded  to  4'74  per  cent,  of  the  so-called  "dry"  acid. 


HISTORICAL  INTRODUCTION.  13 

from   malt   or   other  fermentable   matter   at   any  place 
used  for  the  preparation  of  acetous  acid. 

The  drawback  allowed  by  this  Act,  for  exported 
vinegar  upon  which  the  duty  had  been  paid,  was  sub- 
sequently, in  1821  (I.  and  II.  Geo.  IV.  C.  102),  made 
proportional  to  the  acetic  strength  as  estimated  by  an 
acetometer. 

Four  years  later  (VI.  Geo.  IV.  C.  37),  the  excise  duty 
upon  vinegar  was  again  altered  to  16s.  8d.  for  100  gallons, 
and  by  VI.  Geo.  IV.  C.  81,  the  licence  for  the  manufacture 
of  vinegar  was  fixed  at  £5  per  annum. 

In  the  following  reign  two  Acts  concerning  vinegar 
were  passed.  In  1833  (III.  Gulielm.  IV.  C.  56)  the 
customs  duty  was  fixed  at  £18  18s.  per  tun,  while  in 
1836  (VI.  and  VII.  Gulielm.  IV.  C.  65)  the  Act  of  George 
III.  dealing  with  the  collection  of  the  excise  duty  was 
repealed  so  far  as  it  concerned  the  retailers  of  vinegar. 
This  change  was  made  upon  the  report  of  Commissioners 
who  estimated  that  the  number  of  dealers  and  retailers 
was  very  large  (see  p.  9),  and  that  the  continual  inspec- 
tion of  the  stock  was  expensive  and  unnecessary,  since 
the  duties  might  be  much  more  readily  collected  from 
the  manufacturers. 

In  1840  (III.  Viet.  C.  17)  an  additional  charge  of  5  per 
cent,  upon  the  customs  and  excise  duties  upon  vinegar 
was  imposed,  but  four  years  later  the  excise  duty  upon 
vinegar  was  entirely  abolished  (VII.  and  VIII.  Viet. 
C.  25),  though  a  manufacturer's  licence  was  still  required, 
while  the  customs  duty  was  fixed  at  £4  4s.  per  tun  of 
proof  vinegar  or  acetic  acid  (VII.  Viet.  C.  16).  The 
licence  for  having  a  vinegar  still  or  retort  was  fixed  in 
1846  at  ten  shillings  a  year  (IX.  and  X.  Viet.  C.  90). 


14     VINEGAR  :    ITS   MANUFACTURE   AND   EXAMINATION. 

Proof  Vinegar. — With  the  repeal  of  the  duties  upon 
vinegar  and  acetic  acid,  the  word  "  proof  acid  "  became 
obsolete,  and  the  acetometer,  by  which  the  strength 
was  ascertained,  became  a  curiosity  of  the  past.  The 

ee  -p  » 

terms  "proof/'  —^-,  and  so  on,  still  linger,  however,  in 
oU 

the  vocabulary  of  the  older  workmen  in  vinegar  and 
acetic  acid  works,  while  discarded  acetometers  may 
still  survive  here  and  there,  although  they  have  long 
since  ceased  to  be  made. 

Since,  however,  they  have  historical  interest  in  the 
vinegar  industry,  a  brief  outline  may  be  given  of  the 
method  by  which  the  revenue  officers  determined  the 
strength. 

The  acetometer  was  a  particular  form  of  hydrometer, 
having  a  silver  cup  to  receive  weights  at  the  top  of  its 
stem.  These  weights  were  added  until  the  hydrometer 
sank  in  the  liquid  to  a  mark  made  upon  the  stem.  The 
ucid  or  vinegar  to  be  tested  was  first  diluted  with  an 
equal  volume  of  rain  water,  and  neutralised  by  the 
addition  of  slaked  lime  introduced  in  slight  excess.  As 
considerable  heat  was  produced  by  the  neutralisation, 
the  liquid  was  always  cooled  to  70°  F.  before  testing. 
In  the  case  of  vinegars  an  extra  weight  marked  M 
("  the  mucilage  weight ")  was  used  to  compensate  for 
the  solid  matter,  and  the  reckoning  taken  from  the 
numbered  weights  subsequently  used.  The  weight 

"  10" 
marked  —^ —  indicated  the  strength  of  the  "  best  vinegar  " 

freed  from  solid  matter  ("  mucilage "),  and  was  the 
strength  fixed  by  the  Act  of  George  III.  as  "  proof  acid." 
The  20  weight  indicated  twice  that  strength  of  vinegar, 


HISTORICAL   INTRODUCTION.  15 

the  30  weight  three  times  the  strength,  and  so  on  up  to 
80,  which  corresponded  to  35  per  cent,  over  proof,  or  the 
strongest  acid  upon  which  duty  was  charged  by  means 
of  this  instrument.  There  were  also  three  intermediate 
weights,  8,  4,  2,  and  two  fractional  weights,  1  and  J. 


Fig.  3. — Obsolete  Excise  Acetometer. 

The  specific  gravity  of  the  calcium  acetate  solution  was 
approximately  double  that  of  the  original  acid.  Thus, 
an  acid  of  specific  gravity  1  -009  showed  1  -018  in  the  acetate 
solution.  Vinegar  of  the  same  strength  would  show  about 
1-023,  from  which  0-005  would  be  deducted  for  the 
mucilage  or  extract.  The  proportions  of  acetic  acid 


16     VINEGAR  :    ITS   MANUFACTURE   AND   EXAMINATION. 

corresponding    to   the   acetometer   strengths   were   thus 
as  follows  :  — 

Acetometer,  .       \        1       2    4    8    ^    20    30    40    50    60    70    80 
°'25    °'5     1    2    4      5     10     15    20    25    30    35    40 


As  a  matter  of  fact,  the  strength  of  "  proof  vinegar  " 
was  only  approximately  5  per  cent.,  the  neutralisation 
value  fixed  by  Act  of  Parliament  corresponding  to  a 
vinegar  containing  4-74  per  cent,  of  "  real  "  acetic  acid 
(see  pp.  12,  60). 

The  estimations  of  the  acidity  made  with  this  instru- 
ment were  very  rough,  and  the  variations  in  the  amounts 
of  solid  matter  were  so  great  in  different  vinegars  that 
the  allowance  made  for  them  by  the  "  mucilage  weight  " 
could  at  best  be  only  approximately  correct. 

In  Nicholson's  Dictionary  of  Chemistry  (2nd  ed.),  1823, 
it  is  stated  that  Taylor's  acetometer  was  based  upon  the 
following  table  :  — 

REVENUE  PROOF  ACID,  CALLED  BY  THE 
MANUFACTURER  No.  24. 

Sp.  gr.  1-0085  contains  real  acid  in  100,  .  .  5 

„       1*0170             „                 „  .  .  10 

„       1-0257             „                 „  .  15 

„      1-0320             „                 „  .  20 

„       1-0470             „                 „  .  30 

„       1-0580                               „  .  40 

"  The  acetic  acid  or  radical  vinegar  of  the  apothecaries, 
in  which  they  dissolve  a  little  camphor  or  fragrant  essen- 
tial oil,  has  a  specific  gravity  of  about  1  -070." 

Trade  Numbers  of  Vinegar.  —  As  a  rule,  vinegar  is  not 


HISTORICAL   INTRODUCTION.  17 

sold  to  the  retailers  in  accordance  with  acetic  strength, 
but  is  described  by  the  numbers  16,  18,  20,-  22,  and  24. 

The  origin  of  these  numbers  has  been  attributed  to 
the  price  in  pence  per  gallon  at  which  the  vinegar  was 
once  sold,  but  even  in  1842  it  was  stated  *  that  "  although 
the  price  no  longer  accords  with  these  numbers,  the  num- 
bers themselves  have  been  retained  as  symbols  whereby  a 
certain  quality  of  vinegar  may  be  known  and  designated/' 

This  explanation  is  borne  out  by  Phillips'  Translation 
of  the  Pharmacopceia,  for  the  year  1824,  where  it  is  stated 
that  "  the  strongest  vinegar  is  termed  proof  vinegar, 
and  by  the  manufacturer  called  No.  24.  It  is  estimated 
to  contain  5  per  cent,  of  real  acetic  acid,  and  the  maker 
is  allowed  to  mix  one-thousandth  of  its  weight  of  sul- 
phuric acid  with  it." 

On  p.  18  of  the  same  edition  the  writer  makes  it  clear 
that  by  "  real  "  acetic  acid  is  meant  what  we  now  term 
acetic  anhydride,  but  what  was  then  regarded  as  the 
hypothetical  "  dry  "  acid,  and  he  states  that  50  grains 
of  real  acetic  acid  neutralise  153  grains  of  crystallised 
subcarbonate  of  soda  (i.e.,  crystalline  sodium  carbonate). 
Calculated  upon  this  basis,  the  proof  vinegar  of  the  Act, 
or  No.  24  vinegar,  contained  4-74  per  cent,  of  "  real  " 
acetic  acid,  or  5-5  per  cent,  of  acetic  acid  as  is  now  under- 
stood by  the  term. 

The  other  explanation  of  the  trade  numbers  is  given 
by  Muspratt,f  who  states  that  "  proof  vinegar  has 
a  specific  gravity  of  1-0085,  and  contains  about  5  per 
cent,  of  acetic  acid.  In  commerce  this  vinegar  is 

*  The  Penny  Magazine,  1842,  p.  430.      The  same  explanation  is  also 
given  in  Tomlinson's  Cyclopedia  of  Useful  Arts,  1854,  p.  7. 
t  Dictionary  of  Chemistry,  1860,  p.  32. 

2 


18     VINEGAR  :    ITS   MANUFACTURE   AND   EXAMINATION. 


represented  by  No.  24,  from  the  fact  that  24  grains 
of  pure  dry  carbonate  of  soda  are  required  to  neutralise 
a  fluid  ounce.  Weaker  vinegars  are  represented  by  the 
Nos.  18,  20,  22,  according  to  their  strength;  and,  as  in 
the  foregoing  instance,  these  figures  equal  the  number  of 
grains  of  carbonate  of  soda  that  will  saturate  a  fluid  ounce." 

The  chief  objection  to  this  explanation  is  that  the 
strength  of  proof  vinegar  was  estimated  according  to 
the  Act  of  George  III.,  not  by  means  of  anhydrous  sodium 
carbonate,  but  by  neutralisation  with  "  crystallised 
carbonate  of  soda,"  which  corresponded  to  the  modern 
crystalline  sodium  carbonate  (Na2C03  -f-  10H20).  Accord- 
ing to  this,  proof  vinegar  contained  4-74  per  cent,  of  the 
hypothetical  "  dry "  or  "  real "  acetic  acid,  and  not 
5-27  per  cent.,  as  would  be  required  to  comply  with 
Muspratt's  explanation. 

The  statements  in  Phillips'  Translation  (supra)  are 
conclusive  upon  the  point,  for  they  show  that  the  term 
"  No.  24  "  was  in  use  soon  after  the  passing  of  the  Act. 

On  the  basis  of  this  latter  explanation,  which  was 
accepted  by  many  vinegar  manufacturers,  the  "  numbers  " 
of  the  different  vinegars  would  have  the  following  strengths 
in  terms  of  "  real  "  or  "  dry  "  acetic  acid  and  its  corre- 
sponding modern  equivalent — acetic  acid. 


Xumbev  of  Vinegar. 

"  Dry  "  or  "Real  "  Acetic 
Acid. 

Acetic  Acid. 

Per  cent. 

Per  cent. 

16 

3'4 

4-1 

18 

3'9 

4-6 

20 

4-38 

5-16 

22 

4-76 

5'6 

24 

5-27 

6'2 

HISTORICAL   INTRODUCTION.  19 

In  practice  there  has  been  no  uniformity  upon  this 
point  among  different  manufacturers.  No.  16  vinegar, 
for  example,  has  been  sold  at  strengths  ranging  from 
3-5  to  4-2  per  cent.,  while  No.  24  has  usually  contained 
from  5-5  to  6-0  per  cent,  of  acetic  acid,  and  has  seldom 
been  sold  at  a  strength  of  6-2  per  cent. 

Some  years  ago  a  still  weaker  vinegar  than  No.  16  was 
known  to  the  trade  as  "  Diamond  Vinegar,"  but  since 
the  recommendation  of  the  Local  Government  Board  as 
to  the  strength  of  vinegar,  the  sale  of  any  vinegar 
weaker  than  4  per  cent,  is  liable  to  be  followed  by  a 
prosecution. 


20 


CHAPTER  II. 
THEORIES    OF    ACETIC    FERMENTATION. 

Early  Theories  of  Acetification— Liebig's  Theory— Pasteur's  Views— 
Nageli's  Mechanical  Theory — Later  Enzymic  Theories — The  Enzyme 
of  Vinegar  Bacteria — Oxidation  and  Reduction  Processes. 

Early  Theories  of  Acetification. — The  conditions  neces- 
sary for  the  successful  acetification  of  alcoholic  liquids 
were  known  empirically  long  before  it  was  recognised 
that  the  oxidation  of  alcohol  into  acetic  acid,  as  practised 
in  vinegar  works,  was  of  a  process  analogous  to  the 
fermentation  of  sugar  into  alcohol.  Various  phenomena 
in  the  manufacture  of  vinegar  were  recorded,  but  not 
until  the  19th  century  was  well  advanced  was  there  any 
plausible  attempt  to  explain  their  significance. 

For  example,  in  1822,  Persoon  made  a  microscopical 
study  of  the  films  that  develop  upon  wine  and  beer  when 
exposed  to  the  air,  and  found  them  to  be  made  up  of 
cells  resembling  yeast  cells.  He  gave  to  these  pellicles 
the  general  name  of  Mycoderma  (mucinous  skin),  but 
did  not  associate  them  with  the  development  of 
acidity. 

Berzelius,  in  1829,  extended  his  theory  of  catalytic 
action  to  cover  the  function  of  the  "  mother  of  vinegar  " 
in  acetification,  but  attributed  the  fermentation  not  to 
any  living  cell  or  product  of  a  living  cell,  but  to  the 


THEORIES    OF   ACETIC   FERMENTATION.  21 

action  of  the  acetic  acid  "  enclosed  within  the  pores  " 
of  the  mucinous  skin. 

Then  in  1837  Kiitzing  examined  the  skin,  and  described 
the  small  cellular  structures,  arranged  in  chains,  of  which 
it  was  composed.  He  recognised  that  these  were  living 
organisms,  and  regarded  them  as  algae  (Uvula  aceti),  by 
the  vital  activity  of  which  alcohol  was  transformed  into 
acetic  acid. 

Liebig's  Theory. — In  the  year  1839  Liebig*  published 
his  theory  of  the  nature  of  alcoholic  fermentation,  and 
extended  it  to  cover  also  the  fermentation  of  alcohol 
into  acetic  -acid.  This  theory  had  many  points  in  common 
with  that  of  Stahl  (1697),  for  both  looked  upon  the 
ferment  as  a  body  in  a  state  of  decomposition,  and  capable 
of  imparting  its  motion  to  surrounding  bodies.  Liebig, 
however,  included  all  processes  of  fermentation  under 
ordinary  chemical  actions,  and  in  support  of  his  view 
that  a  small  quantity  of  one  substance  could  bring  about 
changes  in  large  quantities  of  other  substances,  cited 
phenomena  such  as  the  solution  in  nitric  acid  of  platinum 
alloyed  with  silver,  and  the  action  of  nitric  oxide  in  the 
production  of  sulphuric  acid.  4 

-In  particular,  the  fact'  that  platinum  black  could 
promote  the  oxidation  of  alcohol  to  acetic  acid  was 
regarded  by  Liebig  as  a  proof  that  the  ferment  in  vinegar, 
"  the  mother  of  vinegar/'  also  acted  purely  by  chemical 
means.  The  proteins  composing  it  underwent  decom- 
position and  communicated  their  motion. 

Liebig  subsequently  modified  his  opinion  to  the  extent 
that  fermentations  were  caused  by  enzymes  produced 
within  the  living  ceDs,  and  that  the  physiological  growth 
*  J.  prakt.  Chem.,  1.,  35,  312. 


22     VINEGAE  :    ITS    MANUFACTURE   AND    EXAMINATION. 

of  the  cells  had  nothing  to  do  with  the  fermentation 
itself,  but  was  merely  the  means  by  which  the  enzyme 
was  developed.* 

In  another  place  f  he  elaborates  these  views  : — 

"  An  atom  or  molecule  put  in  motion  by  any  power 
whatever  may  communicate  its  own  motion  to  another 
atom  in  contact  with  it. 

"  Hydrogen,  from  being  in  contact  with  decaying 
substances,  acquires  the  power  of  combining  with  oxygen 
at  the  common  temperature. 

"  Other  inflammable  gases,  both  simple  and  com- 
pound, are  affected  under  these  circumstances  in  exactly 
the  same  manner  as  hydrogen.  The  vapour  of  alcohol, 
for  example,  when  in  a  vessel  containing  wood  or  other 
substances  in  a  state  of  decay,  absorbs  oxygen  from  the 
atmosphere,  and  becomes  transformed  into  aldehyde, 
and  subsequently  into  acetic  acid,  which,  upon  assuming 
a  fluid  state,  is  withdrawn  from  the  further  influence  of 
the  oxygen. 

"It  is  upon  this  power  of  substances  undergoing 
decay  to  increase  the  attraction  of  all  organic  substances 
for  oxygen,  and  especially  the  affinity  of  alcohol  for  this 
element  that  a  speedy  process  for  acidifying  alcohol 
was  based,  which  is  termed  the  '  Schnellessig-fabrikation/ 
or  '  quick  vinegar  process.' 

"  The  transformation  of  fermented  liquors  into  vinegar 
formerly  required  weeks,  and  even  months,  to  accomplish 
in  consequence  of  the  imperfect  access  of  the  air  :  we  can 
now  convert  alcohol  into  vinegar  in  less  than  twenty- 
four  hours  ;  and  this  is  effected  mainly  by  making  brandy 

*  Annalen  der  Chem.  u.  Pharm.,  1870,  cliii. 

f  Liebig,  Letters  on  Chemistry,  London,  1851,  p.  216. 


THEORIES   OF   ACETIC   FERMENTATION.  23 

diluted  with  water,  or  any  other  weak  spirituous  liquor, 
trickle  slowly  through  casks  filled  with  wood  shavings, 
and  at  the  same  time  causing  a  slight  stream  of  air  to 
circulate  through  these  shavings. 

"  At  the  commencement  of  this  process  it  is  usual 
to  add  to  the  dilute  spirit  a  small  quantity  of  some  sub- 
stance containing  matter  capable  of  undergoing  the 
process  of  decay,  such  as  beer  wort,  honey,  vinegar, 
etc.  ;  but  after  the  lapse  of  a  very  short  time,  the  surface 
of  the  wood  shavings  passes  into  a  state  of  oxidation, 
and  from  that  moment  effects  the  transformation  of  the 
spirit  into  vinegar  without  the  further  co-operation  of 
extraneous  decaying  matter/' 

In  a  later  paper  *  Liebig  expressed  the  opinion  that 
the  mother-of-vinegar  was  not  essential  to  acetic  fer- 
mentation, but  that  its  place  could  be  taken  by  dead 
vegetable  matter.  "It  is  unquestionable/'  he  says, 
"  that  mother-of-vinegar  is  capable  of  effecting  the 
oxidation  of  alcohol  into  acetic  acid,  but  this  action 
does  not  depend  upon  a  physiological  process.  Alcohol 
requires  for  its  conversion  into  acetic  acid  only  oxygen, 
and  thus  the  Mycoderma  aceti  cannot  and  does  not  give 
to  it  out  of  its  own  substance.  The  analysis  of  the  air 
leaving  the  acetifiers  shows  that  the  oxygen  required 
for  the  oxidation  of  the  alcohol  is  taken  from  the  air, 
and  the  only  part  that  the  mother-of-vinegar  can  take 
in  this  process  is  that  of  promoting  this  absorption  ;  it- 
is  only  active  by  virtue  of  this  chemical  process,  and 
its  place  as  a  living  plant  can  be  taken  by  a  large  number 
of  dead  substances  and  parts  of  plants/' 

Pasteur's  Views  on  Acetiflcation. — The  weight  of  Liebig's 

*  Annalen  der  Chem.  u.  Pharm.,  cliii.,  137. 


24     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

authority  prevented  the  views  of  Kiitzing  (supra)  gaining 
much  acceptance,  and  it  was  not  until  the  year  1864 
when  Pasteur's  experiments  confirmed  the  conclusions 
of  Kiitzing,  that  the  vitalistic  theory  of  acetification 
began  to  prevail,  and  that  the  acetic  fermentation  was 
recognised  as  being  inseparably  connected  with  the 
presence  of  living  organisms. 

fc  V.* 

£:*3fr   :•&  - 


-  Xi  -s  •  i|*«* 

?      l         rV*4    *      V- 


'<-     ,,         -      '  -K»      'V 
1  •      *  „ 


lit 

Fig.  4. — Pasteur's  Drawing  of  Mycoderma  aceti. 

Pasteur  observed  many  of  the  facts  recorded  by  some 
of  his  predecessors,  but  he  made  also  the  first  systematic 
study  of  the  process  of  vinegar-making,  and  was  the 
first  to  prove  that  no  acetic  fermentation  could  take 
place  in  the  absence  of  the  so-called  fungus  Mycoderma. 

Like  Kiitzing,  he  found  that  this  mycoderma  was 
composed  of  distinct  cells,  and  in  a  lecture  given  in 


THEORIES    OF   ACETIC   FERMENTATION.  25 

1868  to  the  vinegar  manufacturers  of  Orleans  he  illus- 
trated the  structure  of  the  "  fungus  "  by  the  drawing 
here  reproduced. 

He  was  the  first  to  suggest  that  a  distinction  should 
be  made  between  the  pellicle  forming  upon  fermenting 
wine  and  that  upon  souring  wine,  and  that  the  name  of 
Mycoderma  vini  should  be  given  to  the  former,  and  that 
of  Mycoderma  aceti  to  the  latter. 

For  very  many  years  these  names  were  generally 
accepted,  but  the  work  of  Hansen  and  others  (infra) 
showed  that  the  organisms  composing  "  mother-of- 
vinegar  "  were  in  reality  bacteria,  and  ought,  therefore, 
to  be  distinguished  from  the  yeasts  which  composed 
the  pellicle  of  Mycoderma  vini.  In  fact,  Pasteur  con- 
cluded that  there  were  many  reasons  for  regarding 
Mycoderma  aceti  as  a  parasite  of  Mycoderma  vini. 

In  his  treatise  upon  the  Fermentation  of  Vinegar,* 
Pasteur  showed  that  the  vinegar  Mycoderma  could  be 
grown  upon  a  neutral  fluid  containing  alcohol,  and  that 
in  its  growth  it  absorbed  oxygen  from  the  air. 

The  experimental  apparatus  by  which  he  proved  this 
fact  is  shown  in  the  accompanying  figure. 

As  the  pellicle  developed  upon  the  liquid  in  the  flask 
the  oxygen  was  slowly  absorbed,  and  the  mercury  con- 
tained in  the  basin,  L,  gradually  rose  in  the  tube  D  E. 
Subsequently  the  gases  remaining  in  the  flask  were 
withdrawn  into  the  eudiometer  F  G  H,  while  the  amount 
of  acetic  acid  produced  was  estimated  by  titration  of 
the  liquid. 

In  answer  to  Liebig's  assertion  (p.  23),  that  the 
function  of  the  Mycoderma  was  a  purely  chemical  one, 

*  Memoire  sur  la  Fermentation  Acetiqve,  Paris,  1868. 


26     VINEGAR  :    ITS    MANUFACTURE   AND    EXAMINATION. 

and  that  its  place  as  a  promoter  of  oxidation  could  be 
taken  by  dead  vegetable  matter,  Pasteur  replied  that, 
while  such  a  notion  was  conceivable,  he  was  not  concerned 
with  this  or  that  theory,  but  only  with  the  fact  that 
every  fermentation  of  alcohol  into  acetic  acid  resulted 
in  the  spontaneous  development  of  Mycoderma  aceti  in 
the  liquid  in  the  casks.  It  was,  moreover,  possible  to 
keep  beer  yeast  for  many  years  in  contact  with  ferment- 


Fig.  5. — Pasteur's  Experiment  illustrating  the  Absorption  of  Oxygen. 

able  fluids,  and  in  communication  with  the  air  in  fer- 
mentation vessels,  without  the  slightest  trace  of  vinegar 
being  produced,  so  long  as  there  were  no  indications 
of  the  appearance  of  Mycoderma  aceti. 

Upon  the  question  of  the  presence  of  a  specific  oxidising 
ferment  as  distinct  from  the  vital  processes  in  the  living 
organism,  Pasteur  did  not  express  any  dogmatic  opinion, 
although  from  the  general  trend  of  his  arguments  he 


THEORIES    OF   ACETIC   FERMENTATION.  2| 

appeared  to  have  a  strong  leaning  towards  the  view 
that  both  alcoholic  and  acetic  fermentations  were  purely 
physiological  processes  inseparable  from  the  lire  of  the 
organisms  effecting  those  fermentations,  and  he  summed 
up  his  position  in  the  matter  by  quoting  the  following 
words  of  Dumas  *  : — "  There  are  doubtless  cases  in  which 
a  secret  agency  of  living  organisms,  such  as,  for  example, 
those  which  are  found  in  association  with  vinegar  fer- 
mentation, is  conceivable  ;  but  so  long  as  the  ferments 
in  question  have  not  been  separated  from  the  rest  of  the 
materials  and  the  phenomenon  attributed  to  them  de- 
monstrated, the  doubt  as  to  their  actual  existence  must 
remain." 

While  recognising  that  the  vinegar  "  fungus''  was  not 
the  same  organism  as  the  wine  "  fungus "  or  yeast, 
Pasteur  did  not  agree  with  the  view  first  put  forward 
by  Stack, f  that  the  vinegar  organism  could  be  classified 
with  the  bacteria. 

Nageli's  Mechanical  Theory.  —  In  1879  Nageli  J  put 
forward  a  mechanical  theory  to  explain  the  nature  of 
fermentation  processes.  According  to  this  theory  the 
molecular  groups  composing  the  protoplasm  of  an  organ- 
ism inducing  fermentation  are  in  a  state  of  molecular 
vibration.  These  vibrations  it  is  able  to  communicate 
to  other  compounds  with  which  it  comes  into  contact, 
so  as  to  produce  also  within  their  molecules  specific 
vibrations  which  result  in  the  destruction  of  the  equili- 
brium and  the  formation  of  new  compounds. 

A  sharp  distinction  is  drawn  between  fermentation 
and  enzymic  action,  the  enzymes  being  regarded  as 

*  Chimie  Appliquee  aux  Arts,  vi.,  341  (1843). 

f  Intellectual  Observer,  1863..  J  Theorie  der  Gcihrung,  1879. 


28     VINEGAR  !    ITS    MANUFACTURE    AND    EXAMINATION. 

replaceable  by  chemical  agents,  whereas  a  ferment  can- 
not exist  apart  from  the  living  cell.  It  is  only  when  work 
is  to  be  done  at  some  distance  from  the  cell  that  the 
organism  excretes  an  enzyme. 

Applying  his  theory  to  the  acetic  fermentation,  Nageli 
suggested  that  the  protoplasm  of  the  acetic^  bacteria 
was  in  a  condition  of  molecular  vibration,  and  that  the 
vibrations  were  imparted,  in  the  first  place,  to  the  mole- 
cules of  alcohol  and  oxygen  that  had  penetrated  into 
the  bacterial  cells,  and  were  thence  communicated  to 
the  molecules  outside  the  cells.  As  soon  as  the  vibrations 
reached  a  certain  pitch  of  intensity  the  molecular  equili- 
brium was  destroyed,  chemical  reaction  took  place,  and 
a  new  series  of  bodies  in  another  phase  of  equilibrium 
was  produced.  Part  of  the  acetic  fermentation  thus 
occurred  within  the  cells  of  the  bacteria,  but  the  greater 
part  took  place  in  the  surrounding  medium.  The  fer- 
mentation was  thus  accomplished  in  two  stages,  the 
equilibrium  of  the  molecules  being  first  destroyed,  and 
new  compounds  then  formed  under  the  influence  of  the 
forces  set  in  motion  by  the  communicated  vibrations. 

Later  Enzymic  Theories. — In  the  later  modification  of 
his  theory  (p.  23),  Liebig  adopted  a  position  which 
receives  experimental  support  from  the  discovery  and 
isolation  of  the  enzymes  in  yeast,  and  later  in  the  acetic 
bacteria  by  Buchner. 

It  has  been  seen  that,  in  their  earlier  form  at  all  events, 
Liebig's  views  were  diametrically  opposed  to  any  such 
vitalistic  theory  as  that  suggested  by  Kutzing. 

According  to  Liebig,  "  mother-of- vinegar  "  was  not 
a  living  organism,  but  consisted  of  structureless  precipi- 
tated albuminous  matter,  which  acted  like  platinum 


THEORIES   OF   ACETIC   FERMENTATION.  29 

black  by  imparting  to  the  oxygen  and  alcohol  its  vibra- 
tions, so  that  these  entered  into  combination. 

Liebig's  final  position  with  regard  to  the  question 
of  enzymes  was  thus  practically  the  same  as  that  held 
by  Traube  *  in  1858.  Traube's  hypothesis  was  that  in 
each  organism  producing  fermentation  there  was  present 
an  enzyme  of  definite  chemical  composition,  which  had 
the  power  of  transferring  oxygen  from  one  part  of  a  group 
of  molecules  to  another.  These  enzymes  were  of  two 
kinds — viz.,  (1)  reducing  enzymes,  which  could  transfer 
combined  oxygen,  as  in  alcoholic  fermentation ;  and 
(2)  oxidising  enzymes,  which  were  capable  of  conveying 
free  oxygen  to  other  bodies,  as  in  the  fermentation  of 
alcohol  into  acetic  acid.  Both  groups  of  enzymes  were 
assumed  to  act  merely  by  conveying  oxygen,  and  not 
by  communicating  their  own  vibrations  to  the  ferment- 
able substances. 

This  theory  of  specific  enzymes  in  bodies  inducing 
fermentation  was  subsequently  developed  by  Hoppe- 
Seyler,  who  concluded  that  the  living  organisms  produced 
the  ferments  required  for  the  particular  fermentation, 
but  that  these  ferments  or  enzymes  were  exceedingly 
unstable  bodies,  which  w^ere  inseparable  from  the  proto- 
plasm, and  became  inactive  when  the  organism  died. 

The  Enzyme  of  Vinegar  Bacteria. — When  Buchner  f 
had  succeeded  in  isolating  the  enzyme  zymase  from  yeast, 
and  in  proving  that  it  was  possible  to  effect  alcoholic 
fermentation  by  means  of  preparations  entirely  free  from 
living  cells,  attempts  were  made  to  separate  enzymes 
from  various  bacteria  by  similar  methods  of  grinding 

*  Theorie  der  Fermentwirkungen,  Berlin,  1858. 
f  B&r.  d.  Chem.  Ges.,  xxx.,  227,  1110. 


30     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

up  the  cells  with  quartz  sand  and  kieselguhr,  and  sub- 
jecting the  mass  to  hydraulic  pressure. 

But  in  every  instance  the  liquids  expressed  from 
acetic  bacteria  were  inert,  and  incapable  of  effecting 
the  oxidation  of  alcohol.  It  thus  appeared  as  though 
the  oxidising  function  of  the  bacteria  were  more  inti- 
mately connected  with  the  vital  processes  of  the  organ- 
isms than  in  the  case  of  the  alcohol-producing  enzyme 
in  yeast,  and  the  failure  of  these  early  experiments  to 
separate  an  oxidising  enzyme  confirmed  the  views  of 
those  who  held  that  the  acetic  fermentation  was  purely 
a  physiological  process.  It  was  only  because  the  oxida- 
tion was  an  exothermic  process  of  a  specific  character 
that  there  was  any  evidence  for  still  regarding  the  acetic 
fermentation  as  being  due  to  a  definite  enzyme. 

It  was  not  until  1 906  that  Buchner  and  Gaunt  *  suc- 
ceeded in  demonstrating,  by  a  totally  different  method, 
that  such  acetic  enzymes  really  existed.  The  pellicles 
of  "  mother-of- vinegar  "  forming  upon  alcoholic  liquids 
in  course  of  acetification  were  freed  from  water  by  centri- 
fugal force,  and  the  residual  mass  of  bacteria  was  treated, 
while  still  moist,  with  acetone.  The  resulting  fluid 
acetone  preparations  were  stable  and  capable  of  oxidising 
alcohol.  Any  possibility  of  living  cells  was  eliminated 
by  adding  a  small  amount  of  toluene.  The  preparations 
made  from  cultivations  of  bacteria  grown  at  10°  to  22°  C. 
were  more  active  than  those  grown  at  28°  C.  In  the 
experimental  fermentations  the  stable  acetone  prepara- 
tions were  ground  to  a  paste  with  2  to  4  per  cent,  of 
alcohol  and  chalk  and  4  per  cent,  of  toluene,  and  the 
mixtures  were  exposed  for  three  days  to  a  current  of 

*  Annalen,  1906,  cccxlix.,  140. 


THEORIES    OF   ACETIC   FERMENTATION.  31 

air  at  28°  C.  As  a  rule,  not  more  than  0-5  to  2  per  cent, 
of  acetic  acid  was  obtained,  the  maximum  yield  being 
4  per  cent. 

The  preparations  also  possessed  the  same  property  as 
the  living  bacteria  of  oxidising  propyl  alcohol  to  pro- 
pionic  acid.  From  the  results  of  these  experiments  there 
can  be  no  reason  for  doubting  that  acetic  bacteria  owe 
their  oxidising  powers  to  the  presence  of  one  or  more 
enzymes. 

It  has  recently  been  found  by  Wieland  *  that  the 
enzyme  thus  prepared  from  Hansen's  B.  aceti  may  be  used 
instead  of  palladium  black  as  a  catalytic  agent  for  the  con- 
version of  alcohol  into  acetic  acid,  and  that  it  is  capable 
of  effecting  the  change  in  the  absence  of  free  oxygen, 
provided  that  a  substance  such  as  quinone  or  methylene 
blue  is  present.  The  function  of  the  oxygen  in  the  methyl- 
ene blue  is  to  absorb  the  liberated  hydrogen,  and  thus 
prevent  its  combining  with  the  palladium  and  rendering 
it  inactive.  In  the  light  of  these  experiments,  the  enzymic 
process,  which  is  usually  regarded  as  one  of  oxidation, 
must  be  regarded  as  a  dehydrogenation  process.  In 
fact,  Wieland  considers  that  he  is  justified  in  regarding 
all  oxidations  as  due  to  dehydrogenation,  and  that  there 
is  in  reality  no  essential  difference  between  processes  of 
reduction  and  of  oxidation. 

*  Ber.  d.  Chem.  Qes.,  1913,  xlvi.,  3327. 


CHAPTER  III. 
THE    ACETIC   BACTERIA. 

Mycoderma  aceti — Hansen's  Three  Species — Zoogloeal  Condition — In- 
volution Forms — Other  Acetic  Bacteria — Action  of  Light  on  Acetic 
Bacteria — Use  of  Pure  Cultures. 

The  Mycoderma  aceti. — For  many  years  after  their 
discovery  the  small  organisms  that  compose  the  struc- 
ture of  "  mother-of- vinegar  "  were  regarded  as  mould 
fungi  or  yeasts,  the  superficial  resemblances '  between 
the  pellicle  formed  upon  liquids  in  course  of  acetification 
and  that  formed  upon  wine  by  the  yeast  then  termed 
Mycoderma  vini  lending  support  to  this  view. 

The  suggestion  of  Stack  (p.  27)  that  Mycoderma  aceti 
was  produced  by  bacteria  was  not  accepted  by  Pasteur 
(1868),  notwithstanding  the  fact  that  he  states  he  had 
observed  under  the  microscope  indications  of  the  multi- 
plication of  the  cells  by  fission.*  One  of  the  earliest 
authorities  to  recognise  the  nature  of  these  micro-organ- 
isms was  Cohn,f  who  in  1872  included  them  among  the 
bacteria. 

Hansen's  Three  Species. — It  was  not  until  1878,  when 
Hansen  J  published  the  results  of  his  investigation  into 
the  nature  of  the  micro-organisms  that  cause  beer  to  turn 

*  Loc.  tit.,  p.  63. 

fCohn,  Beitrage  zur  Biologie  der  Pflanzen,  ii.,  127  (1872). 

J  See  Compt.  Rend.  Lab.,  Carlsberg,  1894,  iii. ;  1900,  v. 


THE   ACETIC   BACTERIA. 


33 


sour,  that  it  became  known  that  the  acetic  fermentation 
might  be  brought  about  by  several  species  of  bacteria. 

Subsequently  it  was  discovered  by  Lafar  *  that  at 
least  one  species  of  budding  fungi  was  capable  of  effecting 
the  conversion  of  alcohol  into  acetic  acid. 

The  three  species  of  acetic  bacteria  which  were 
thoroughly  studied  by  Hansen  f  were  given  the  names  of 
Bacterium  aceti,  B.  Pasteurianum,  and  B.  Kutzingianum, 
and  they  differ  from  each  other  in  their  form  and  their 
behaviour  when  grown  upon  an  alcoholic  culture-medium 
such  as  beer. 


Fig.  6. — Bacterium  aceti 
(after  Hansen). 


Fig.  7. — Bacterium  Pasteurianum 
(after  Hansen). 


Bacterium  aceti,  when  grown  in  beer  exposed  to  the 
air,  at  a  temperature  of  about  34°  C.,  speedily  develops  a 
moist  smooth  skin,  in  which  are  markings  resembling  veins. 

B.  Pasteurianum  also  develops  a  pellicle  within  twenty- 
four  hours,  but  the  skin  in  this  case  is  dry  and  has  a 
corrugated  appearance. 

*  Compt.  Rend.  Lab.,  Carlsberg,  1894,  p.  182. 
f  Centrcitbl.  Balder.,  1893,  xiii.,  1864. 


34     VINEGAR  :    ITS    MANUFACTURE   AND    EXAMINATION. 


B.  Kiltzingianum  forms  a  skin  somewhat  resembling 
that  produced  by  B.  aceti,  but  differing  from  it  in  the 
way  in  which  it  spreads  upwards  at  the  edges.  It  also 
causes  turbidity  in  the  liquid,  after  cooling,  which  is  not 
the  case  with  the  other  two  species. 

The  general  appearance  of  the  cells  composing  the 
pellicles  formed  by  these  three  species  is  shown  in  Fig.  6. 

It  will  be  noticed  that  the  cells  of  B.  aceti  are  smaller 
and  narrower  than  those  of  the  other  two  species,  and 
that  they  form  more  compact  chains  than  B.  Pasteur- 
ianum.  In  the  case  of  B.  Kutzingianum  isolated  cells  are 


Fig.  8. — Bacterium  Kutzingianum 
(after  Hansen). 


Fig.  9. — Bacterium  Pastevrianum 
— Zoogloeal  Formation. 


the  rule,  and  chain  formations  the  exception.  The  con- 
stricted "  figure-of-eight "  forms  observed  by  Pasteur  is 
a  frequent  characteristic  of  the  cells  of  B.  Pasteur ianum. 

Zoogloeal  Conditions. — The  curious  pellicles  formed  by 
these  and  other  acetic  bacteria  upon  the  surface  of  the 
liquid  in  which  they  develop  are  zooglceal  forms  produced 
by  the  swelling  and  cohesion  of  the  walls  of  adjacent  cells 
into  a  compact  mucinous  mass. 

When  a  portion  of  one  of  these  pellicles  is  examined 
under  the  microscope,  the  structure  of  the  mucinous 


THE    ACETIC    BACTERIA. 


35 


layer  between  the  cells  is  invisible,  but  when  stained  by 
Loffler's  method  the  cells  may  be  seen  imbedded  in  their 
gelatinous  envelope. 

An  example  of  this  is  shown  in  Fig.  9,  which  represents 
a  portion  of  the  pellicle  of  B.  Pasteur ianum  stained  in 
this  manner.  The  three  lowest  spaces  on  the  left  show 
the  mucinous  membrane  devoid  of  the  bacterial  cells, 


Fig.  10. — Morphological  Changes  of  jB.  Pasteurianum. 

these  having  been  crushed  during  the  preparation  of  the 
specimen. 

The  mucinous  membrane  of  one  of  Hansen's  three 
species,  B.  Kiitzingianum,  when  freshly  grown  upon  a 
nutrient  liquid,  may  be  stained  blue  by  a  solution  of 
iodine,  and  when  now  examined  under  the  microscope 
the  cells  (stained  yellow)  will  be  seen  enveloped  in  a  blue 
medium.  In  the  case  of  the  other  two  species  the  cells 


36    VINEGAR  I    ITS   MANUFACTURE   AND   EXAMINATION. 

are    stained    yellow    by  the    iodine,    but    the  mutinous 
membrane  remains  colourless. 

Involution     Forms    of     Acetic    Bacteria. — A    remarkable 


Fig.  11. — Thread  Formation  of  B.  Pasteurianum. 

property,  which  appears  to  be  common  to  all  the  species 
of  acetic  bacteria,  is  that  of  changing  its  form  under  the 
influence  of  temperature.  The  discovery  and  investiga- 


THE   ACETIC   BACTERIA. 


37 


tion  of  this  phenomenon  by  Hansen*  formed  part  of  a 
research  which  has  now  become  a  classic. 

Hansen  found  that   when  the   cells  of  the  bacteria, 


Fig.  12. — Transformation  of  B.  Pasteurianum. 

freshly  grown  at  34°  C.  (see  Fig.  10),  were  transferred 
to  a  similar  medium  (a  light  beer),  and  maintained  at  a 

*  Loc.  cit. 


38     VINEGAR  :    ITS    MANUFACTURE   AND    EXAMINATION. 


temperature  of  about  40°  C.,  long  rod-shaped  forms  were 
developed  (Fig.  10),  and  these  gradually  extended  into 
long  threads,  some  of  which  attained  a  length  of  200  /u. 
(Fig.  11). 

On  now  exposing  these  filaments  to  the  initial  tem- 
perature of  34°  C.  they  began,  after  a  few  hours,  to  pro- 
duce bulbous  swellings  in  different  places  (Figs.  12, 14),  and 
finally  both  the  rods  and  the  bulbous  cells  become  split 
up  into  short  rods  (Fig.  13),  leaving  only  the  thick  walls 
of  the  bulbous  cell  (d,  Fig.  13)  unchanged. 


a 


Fig.  13. — B.  Pasteurianum — Residue  of  Swollen  Threads. 

On  examining  the  culture  after  twenty-four  hours, 
all  signs  of  the  long  thread  formation  had  disappeared 
and  the  bacteria  had  reverted  to  their  original  form  of 
chains  of  cells  (Figs.  10,  14). 

These  morphological  changes  were  thus  mainly  de- 
pendent upon  the  temperature  of  cultivation,  although 
they  were  also  influenced  by  the  composition  of  the 


Fig.  14. — B.  Pasteurianum — Conversion  of  Threads  into  Chains  of  Short  Rods. 


THE   ACETIC   BACTERIA. 


culture  medium  and  the  age  of  the  bacteria.  Cells  that 
were  more  than  two  days  old  formed  the  long  filaments 
with  much  less  readiness  than  quite  young  cells. 

Similar  involution  forms  were  observed  in  the  case 


Fig.  15.— Filaments  of  B.  aceli. 


40     VINEGAR  :    ITS   MANUFACTURE   AND   EXAMINATION. 

of  the  other  two  species  discovered  by  Hansen.  The 
filaments  produced  by  B.  aceti  were  thinner,  and  attained 
more  than  twice  the  length  of  those  formed  by  B.  Pasteur  ~ 
ianum  (see  Fig.  15),  while  occasionally  branchings  were 
observed  (Fig.  16). 


Fig.  16.— B.  aceti— Unusual  Forms. 

On  the  other  hand,  the  filaments  of  B.  Kutzingianum, 
were  much  shorter  than  those  of  the  other  two  species. 
Hansen  also  recorded  the  occurrence  of  analogous  for- 
mations, when  other  species  of  acetic  bacteria,  including 


THE   ACETIC  BACTERIA.  41 

those  discovered  by  Zeidler,*  were  cultivated  at  higher 
temperatures. 

Other  Acetic  Bacteria. — A  species  of  acetic  bacteria 
quite  distinct  from  those  described  by  Hansen  was 
isolated  by  A.  J.  Brown  f  from  malt  wort  in  course  of 
acetification,  while  three  new  species  were  isolated  by 
Henneberg  J  in  1897,  and  several  more  later.§ 

There  is  some  reason  for  doubting  whether  all  these 
species  are  really  distinct  or  whether  some  are  not  merely 
involution  forms  of  others  due  to  variations  in  the  culture 
media. 

Bacillus  xylinus  (Brown). — The  bacilli  are  non-motile 
rods  1  to  2 /x  in  length  by  0-5  /x  mean  breadth,  and  under 
the  influence  of  increased  temperature  form  filaments 
10  to  30  /x  long  by  0-5  /m  in  breadth.  They  produce  a 
tough,  gelatinous  pellicle,  which  may  grow  to  several 
inches  in  thickness.  At  first  this  skin  is  transparent, 
but  later  becomes  opaque  and  leathery. 

It  is  the  zooglceal  condition  of  this  and  allied  species 
of  bacteria  which  constitutes  the  so-called  "  vinegar 
plant,"  and  the  excessive  development  of  which  causes 
trouble  in  the  working  of  the  acetifiers  in  the  factory. 

It  was  shown  by  Brown  ||  that  when  the  pellicle  was 
freed  from  fat,  etc.,  by  extraction  there  remained  a  mass 
which  gave  the  reactions  of  cellulose  (solubility  in  ammoni- 
acal  copper  oxide,  blue  coloration  with  iodine  and  sul- 
phuric acid)  and  had  a  composition  corresponding  to 
the  formula  (C6H1005)M. 

*  Centralbl.f.  Bakt.,  1896,  ii.  f  Journ.  Chem.  Soc.,  1886,  xxxix.,  432. 

J  Die  Deutsche  Essig-industrie,  1898,  ii.,  Nos.  14-15. 

§  Ibid.,  1905,  Nos.  49-51. 

\\Journ.  Chem.  Soc.,  1886,  xxx.,  432  ;   Proc.  Chem.  Soc.,  1887,  87. 


42     VINEGAR  I    ITS    MANUFACTURE   AND    EXAMINATION. 

Bacillus  oxydans  (Henneberg). — This  forms  rods  2-4  to 
2-7  JUL  in  length  by  0-8  to  1  /*  in  breadth,  which  frequently 
produce  long  undulating  filaments.  It  forms  a  thin 
mucinous  pellicle,  which  does  not  give  a  blue  coloration 
with  iodine.  Apparently  this  bacillus  is  identical  with 
the  Bacterium  aceti  of  Zopf . 

Bacillus  acetosus  (Henneberg). — The  bacilli  are  about 
1  fjL  long  by  0-5  yu  in  breadth,  and  form  long  filaments 
resembling  those  of  B.  Pasteurianus  in  appearance. 
They  produce  a  very  tough,  adherent  pellicle,  which  does 
not  give  a  blue  coloration  with  iodine. 

Bacillus  acetigenus  (Henneberg). — This  is  distinguished 
from  the  preceding  species  by  yielding  a  soft  mucinous 
pellicle,  which  gives  a  blue  coloration  with  iodine  and 
contains  cellulose.  It  is  one  of  the  species  which  effects 
the  acetification  in  German  vinegar  works. 

Bacillus  Orleanensis  (Henneberg). — This  species  is  stated 
by  Henneberg  to  effect  rapid  acetification.  It  forms 
a  very  tough  skin,  which  subsequently  when  older 
becomes  polished  and  closely  resembles  silk  paper.  The 
bacilli  form  small  rods  (1-5  to  2-5  //,  by  0-4  to  0-5 /x), 
which  frequently  develop  into  long  filaments.  They 
will  not  grow  at  8°  C.  or  at  39°  C.,  the  optimum  tempera- 
ture being  20°  to  25°  C.  The  pellicle  does  not  give  a  blue 
coloration  with  iodine. 

Bacillus  curvus  (Henneberg). — This  species,  in  accord- 
ance with  its  name,  has  a  pronounced  tendency  toward 
the  formation  of  curved  rods  (1-6  to  4/x  by  0-4  to  0-5  yu), 
which  may  occur  singly  or  in  chains.  It  only  produces 
a  very  small  quantity  of  pellicle,  which  may  form  small1 
white  patches  on  the  surface  of  the  liquid. 

Bacillus    rancens    (Beijerinck). — A    species    of    bacilli 


THE   ACETIC   BACTERIA.  43 

isolated  by  Beijerinck  *  from  a  beer  vinegar  had  the 
property  of  inverting  cane  sugar. 

Several  forms  of  bacteria  were  also  separated  by 
Perold  f  from  sour  wine,  and  termed  B.  aceti  vini.  He 
regarded  them  as  quite  distinct  from  other  species  that 
have  been  described. 

Bacillus  Schiltzenbachii  (Henneberg). — This  was  found 
by  Henneberg  in  the  gyle  of  a  vinegar  brewery.  It 
forms  ovoid  or  elongated  rods  (1-6  to  2-4/x  in  length  by 
0-3  to  0-4//  in  breadth),  which  may  be  isolated  or  in 
chains.  When  grown  on  a  nutrient  liquid  it  produces 
pellicles  which  are  at  first  in  patches,  but  afterwards 
coalesce,  while  a  light  powdery  deposit  forms  at  the 
bottom  of  the  vessel.  The  pellicle  does  not  give  a  blue 
coloration  with  iodine. 

Bacillus  xylinoides  (Henneberg). — Another  species,  iso- 
lated by  Henneberg  in  1906  from  vinegar  "  wash/'  may 
produce  either  a  thin,  fairly  tough  pellicle,  or  a  coarse 
mucinous  skin  resembling  coagulated  white  of  egg.  The 
latter  zoogloeal  condition  resembles  the  "  vinegar  plant " 
formed  by  B.  xylinus,  and,  like  the  latter,  gives  the 
cellulose  reaction  with  iodine  and  sulphuric  acid.  The 
other  modification  of  the  pellicle  does  not  give  this  re- 
action. The  bacilli  are  rods  from  1-2  to  2  /x  in  length  by 
0-5  to  0-8  p  in  breadth.  They  will  not  develop  at  6°  C., 
and  only  grow  slightly  at  15°  C.  Their  optimum  tem- 
perature is  28°  C.,  and  at  359  C.  all  growth  stops. 

Bacillus  vini  acetati  (Henneberg). — As  its  name  implies, 
this  species  was  found  in  wine  in  course  of  acetification. 
It  forms  a  tender  pellicle,  and  at  first  causes  the  liquid 
to  become  turbid.  The  bacilli  (1  to  2 /x  long  by  0-4/x 

*  Centralbl  /.  BaU.,  1898,  iv.  (2),  209.  f  Ibid.,  1909,  xxiv.,  13. 


44     VINEGAR  :    ITS   MANUFACTURE   AND   EXAMINATION. 

broad)  only  occasionally  form  filaments.  Growth  is 
feeble  at  15°  C.  and  at  36°  C.,  and  stops  at  8°  C. 

Effect  of  Light  on  Acetic  Bacteria. — Like  all  micro- 
organisms, the  vitality  of  the  acetic  bacteria  is  reduced 
by  sunlight,  and  this  was  recognised  long  before  the 
nature  of  acetic  fermentation  was  known. 

Thus,  for  example,  in  one  of  the  earliest  German 
technical  treatises  on  the  manufacture  of  vinegar,*  a 
description  is  given  of  the  method  of  fermentation  in 
casks,  which  are  termed  Mutterfasser.  This  process  in 
its  essential  details  is  the  same  as  the  Orleans  method 
described  in  the  Transactions  of  the  Royal  Society  (see 
p.  6),  but  stress  is  laid  upon  the  point  that  all  daylight 
should  be  excluded  from  the  room,  as  far  as  possible,  and 
that  even  candle-light  should  only  be  used  when  abso- 
lutely necessary. 

Experiments  upon  a  small  scale  made  in  1891  by 
Giunti  f  showed  that  acetic  fermentation  was  inhibited 
by  the  direct  rays  of  the  sun,  and  that  even  diffused 
daylight  checked  the  development  of  the  bacteria  in 
those  parts  of  the  liquid  that  it  could  reach.  These 
results  were  confirmed  in  1891  by  Tolomei,f  who  also 
extended  the  experiments  to  ascertain  which  of  the 
rays  affected  the  fermentation.  Nine  samples  of  the  same 
white  wine  were  placed  in  a  series  of  flasks,  one  of  which 
was  of  ordinary  colourless  glass,  another  being  blackened, 
while  the  rest  were  coloured  in  accordance  with  the 
colours  of  the  spectrum.  After  the  lapse  of  22  days  the 
amounts  of  alcohol  and  acetic  acid  were  estimated  in 
each  of  the  flasks,  with  the  following  results  : — 

*  Juch,  Die  Kunst  der  Essig-Bereitung,  Niirnberg,  1818. 
t  Quoted  by  Franche,  Fdbricant  de  Vinaigre,  p.  37. 


THE   ACETIC   BACTERIA. 


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46     VINEGAR  I    ITS    MANUFACTURE   AND    EXAMINATION. 

These  results  are  very  striking.  They  show  a  steady 
increase  in  the  amount  of  acetic  acid  formed  from  violet 
to  red,  and  prove  that  the  violet  rays  of  light  are  those 
that  are  injurious  to  acetic  fermentation. 

The  precautions  taken  by  the  old  vinegar  makers  to 
exclude  daylight  as  far  as  possible  have  thus  a  scientific 
justification.  When  dealing  with  small  casks,  into  the 
top  oc  which  the  vinegar  was  poured,  such  constant 
exposure  of  the  bacteria  to  the  light  must  have  had  an 
injurious  effect  upon  their  development  and  action. 

The  experiments  cited  show  that  by  placing  windows 
of  orange  glass  in  the  room  the  fermentation  would  have 
proceeded  as  weh1  as  in  darkness. 

When  "  stoves  "  for  the  large  English  acetifiers,  con- 
taining 3,000  to  4,000  gallons,  were  first  erected,  the 
tradition  of  darkness  was  maintained,  but  the  conditions 
of  acetification  on  such  a  large  scale  are  quite  different 
from  those  that  obtain  in  acetification  in  small  casks. 

Even  when  there  is  a  top  window,  the  amount  of  light 
that  can  find  its  way  into  the  acetifiers  through  the 
small  holes  in  the  sides  of  the  vats  is  quite  negligible, 
and  the  author  has  proved  by  an  experience  of  several 
years  that  it  is  possible  to  have  sufficient  light  in  the 
building  without  interfering  in  any  way  with  the  steady 
working  of  the  acetifiers. 

Use  of  Pure  Cultures  of  Acetic  Bacteria. — The  isolation 
of  the  particular  species  of  bacteria  most  suitable  for  the 
preparation  of  different  kinds  of  vinegar,  and  their  use 
as  pure  cultures  for  acetification,  would  probably  give 
very  satisfactory  results  in  producing  vinegars  with 
different  flavours,  and  for  rapid  working  with  different 
types  of  apparatus. 


THE    ACETIC   BACTERIA.  47 

For  example,  the  bacteria  (B.  xylinus,  etc.)  which 
form  the  "  vinegar  plant  "  do  not  work  satisfactorily 
in  some  of  the  Continental  forms  of  apparatus,  since 
the  heavy  gelatinous  slime  they  produce  soon  tends 
to  choke  any  fine  openings,  while,  on  the  other  hand, 
some  of  the  other  species  work  best  at  too  low  a  tempera- 
ture to  suit  the  large  English  acetifiers,  which  derive 
their  heat  from  rapid  auto-oxidation. 

This  is,  of  course,  assuming  that  the  Continental 
species  of  bacteria  would  not,  if  grown  for  many  gener- 
ations in  malt  wash  under  the  conditions  of  the  manu- 
facture in  England,  gradually  assume  the  "  slime-forming  " 
capacity  of  B.  xylinus. 

So  far,  very  little  work  has  been  done  to  ascertain 
the  effects  of  using  pure  species  of  the  bacteria  in  cultures 
prepared  upon  lines  similar  to  those  first  employed  by 
Hansen  in  growing  pure  cultivations  of  yeast  from  a 
single  cell. 

It  was,  however,  shown  some  fifteen  years  ago  that 
each  individual  species  has  the  power  of  producing  a 
vinegar  of  different  quality  and  aroma  from  the  same 
wine. 

Thus  Villon  *  describes  the  results  of  his  experiments 
on  this  point  in  the  following  words  : — "  We  have  dis- 
tinguished several  varieties  of  Mycoderma  aceti,  and 
each  of  them  has  the  property  of  producing  a  vinegar 
of  characteristic  flavour  and  aroma. 

"  We  have  been  able  to  make  a  selection  from  these 
varieties,  in  exactly  the  same  way  as  has  been  done  in 
the  case  of  the  yeasts  of  beer,  wine,  and  cider.  We  have 

*  Quoted  by  Franche,  Manuel  Pratique  du  Fabricant  de  Vinaiyre,  1901, 
p.  64. 


48     VINEGAR  I    ITS   MANUFACTURE    AND    EXAMINATION. 

isolated  three  distinct  varieties,  which  we  term  I.,  II., 
and  III. 

"  My  coder  ma,  aceti  No.  I.  produces  an  exquisite  vinegar, 
which  keeps  well.  It  acetifies  wine  and  vinegar  less 
rapidly  than  the  other  two  varieties,  and  also  grows 
old  more  rapidly. 

"  My  coder  ma  aceti  No.  II.  gives  an  ordinary  vinegar 
of  average  keeping  qualities.  It  acetifies  more  rapidly 
than  the  variety  No.  I.,  and  keeps  for  an  average  length 
of  time.  It  is  the  sort  of  most  common  occurrence  in 
ordinary  vinegar  works. 

"  Mycoderma  aceti  No.  III.  produces  a  turbid,  flat 
vinegar,  which  keeps  extremely  badly.  It  acetifies  more 
rapidly  than  the  others — in  fact  too  rapidly,  since  it 
oxidises  the  substances  that  form  the  bouquet. 

"  We  are  convinced  that  there  are  other  varieties  of 
Mycoderma  aceti,  but  up  to  the  present  we  have  only 
been  able  to  isolate  these  three  from  those  which  acetify 
wine. 

"  It  would  be  advantageous  to  make  use  only  of 
Mycoderma  No.  I.,  and  to  prevent  the  formation  of  No.  II., 
and  especially  of  No.  III.  We  have  isolated  this  variety 
No.  I.  from  Burgundy  wine  of  an  alcoholic  strength  of 
exactly  9  per  cent,  in  process  of  acetification  at  a  tem- 
perature of  20°  C.  The  wine  was  treated  with  1  gramme 
of  ammonium  phosphate  per  litre.  We  then  made  a 
series  of  twenty  cultivations  in  succession,  the  Mycoderma 
aceti  not  being  left  for  longer  than  24  hours  in  each  new 
wine,  which  had  previously  been  aerated  in  a  current  of 
oxygen  and  filtered  through  porous  porcelain  to  remove 
foreign  ferments. 

"  We  thus  obtained  a  cultivation  of  Mycoderma  which 


THE   ACETIC   BACTERIA.  49 

was  pure,  young,  and  very  vigorous.  It  was  with  the 
plant  thus  cultivated  that  we  inoculated  the  wine  that 
was  to  be  acetified  on  an  industrial  scale.  The  ferment 
was  only  suitable  for  two  acetifications,  after  which  it 
had  to  be  replaced  by  a  fresh  pure  culture.  In  this  way 
a  vinegar  with  an  excellent  flavour  and  remarkable 
aroma  was  obtained/' 

It  is  to  be  feared  that  too  little  stress  is  laid  upon  the 
aroma  of  the  vinegar  brewed  in  England  to  make  the 
use  of  pure  cultures  of  bacteria  appreciated  from  this 
point  of  view.  On  the  other  hand,  it  is  possible  that  by 
the  use  of  cultures  of  special  species  the  loss  of  acid 
during  acetification  might  be  materially  reduced. 


50 


CHAPTER  IV. 
CHEMICAL    REACTIONS    IN    ACETIFICATION. 

Earlier  Views — Oxidation  in  Acetification — Effects  of  Oxidation — Acet- 
aldehyde — Acetal — Ethyl  Acetate — Other  Products — Oxidation  of  the 
Acetic  Acid — Oxidation  effected  by  Platinum  Black. 

Earlier  Views. — The  part  played  by  the  air  in  the  conver- 
sion of  wine  into  vinegar  was  recognised  in  practice  long 
before  any  attempt  was  made  to  explain  the  facts. 

In  the  year  1778  Macquer  described  in  his  Dictionaire 
de  Chimie  an  experiment  made  by  Becher,  the  results 
of  which  were  supposed  to  show  that  wine  was  con- 
verted into  stronger  vinegar  than  usual  when  heated  in 
a  hermetically  sealed  flask — i.e.,  without  the  assistance  of 
the  air.  Some  years  later  the  Abbe  R-ozier  *  proved  that 
absorption  of  air  took  place  in  the  course  of  acetification. 
He  attached  a  bladder  distended  with  air  to  a  tube  passing 
through  the  bung  of  a  cask  containing  wine  that  was 
turning  sour  ;  and  he  found  that  the  more  acid  the  wine 
became  the  more  limp  was  the  bladder. 

Oxidation  in  Acetifieation. — Rozier  did  not  draw  any 
decisive  deductions  from  this  experiment,  and  it  was 
left  for  Lavoisier  f  to  show  that  it  was  not  the  whole  of 
the  air,  but  the  oxygen  contained  in  it,  that  was  the 
active  agent  in  acetification. 

*  Dictionaire  d' Agriculture,  1786,  iv.,  525. 
t  Trait*  de  Chimie,  1793,  i.,  159. 


CHEMICAL   REACTIONS   IN   ACETIFICATION.  51 

"  The  acetic  fermentation,"  he  wrote,  "  is  nothing 
more  than  an  acidification  of  the  wine  effected  in  the 
open  air  by  absorption  of  oxygen." 

The  nature  of  alcohol  and  acetic  acid  was  not  under- 
stood at  that  period,  and  hence  Lavoisier  made  no  sugges- 
tion as  to  how  the  absorbed  oxygen  acted  during  aceti- 
fication. 

The  theory  put  forward  by  Berthollet  *  to  explain 
the  effect  of  the  absorption  in  Rozier's  experiment  was 
that  the  oxygen  probably  effected  the  decomposition 
of  the  vinous  compound,  by  abstracting  and  combining 
with  the  hydrogen  therein  so  as  to  form  acetic  acid,  and 
it  is  interesting  to  note  that  this  view  has  recently  received 
support  from  the  experiments  of  Wieland  (p.  31)  upon 
the  behaviour  of  the  vinegar  enzyme  in  the  absence  of 
free  oxygen. 

The  next  observations  published  upon  the  chemical 
process  of  acetification  were  those  of  de  Saussure,f  who 
claimed  that  he  had  found  that  during  the  acetic  fer- 
mentation a  volume  of  carbon  dioxide  equal  to  that  of 
the  absorbed  oxygen  was  liberated,  and  that  the  aceti- 
fication of  wine  depended  not  upon  a  fixation  of  oxygen, 
but  upon  the  withdrawal  of  carbon  and  its  partial  libera- 
tion in  the  form  of  carbonic  acid. 

Effects  of  Oxidation,— It  was  not  until  1821  that 
definite  proof  of  the  nature  of  the  oxidation  process  was 
brought.  In  that  year  E.  Davy  {  discovered  platinum 
black,  and  showed  that  when  it  was  moistened  and 
treated  with  spirits  of  wine  it  became  white  hot  and 

*  Statique  Chimique,  1803,  ii.  (Appendix),  525. 

t  Recherches  Ckimiques  sur  la  Vegetation,  1804,  p.  143. 

$Schweigger'sJourn.,  1821,  i.,  340. 


52    VINEGAR  :    ITS   MANUFACTURE   AND   EXAMINATION. 

caused  the  alcohol  to  be  oxidised  to  acetic  acid  without 
any  carbon  dioxide  being  formed.  It  was  this  observa- 
tion which  suggested  to  Dobereiner  *  his  equation  of  the 
oxidation  of  alcohol  in  the  acetic  fermentation — 

C4H602  +  40  =  C4H404  +  2(HO),t 
or  translating  this  into  modern  formulae — 

CH3CH2OH  +  20  =  CH3 .  COOH  -j-  H20, 

and  he  confirmed  this  by  quantitative  experiments. 

In  accordance  with  his  results,  Dobereiner  explained 
the  acetic  fermentation  as  a  simple  process  of  oxidation t 
which  was  brought  about  through  the  agency  of  a  body,, 
such  as  platinum  black,  capable  of  condensing  and 
absorbing  the  oxygen,  so  as  to  bring  it  into  close  contact 
with  the  alcohol. 

Acetaldehyde. — Dobereiner  also  described  a  "  light 
oxygen  ether,"  which  he  obtained  by  distilling  alcohol 
with  manganese  dioxide  and  sulphuric  acid.  This  sub- 
stance, which  was  impure  aldehyde,  was  subsequently 
studied  by  Liebig,  who  gave  it  its  name  (Alcohol  dehydrogen- 
atus),  and  showed  that  it  was  produced  as  an  intermediate 
stage  in  the  oxidation  of  alcohol  to  acetic  acid. 

The  course  of  the  fermentation  would  thus  take  place 
in  two  stages,  in  the  first  of  which  the  alcohol  was  oxidised 
to  aldehyde — 

C2H60  +  O  =  C2H40  +  H20, 

while  on  further  oxidation  the  aldehyde  became  acetic 
acid — 

C2H40  +  0  =  C2H402. 

*  Ibid.,  viii.,  321.  f  C  =  6  ;  0  =  8. 


CHEMICAL  REACTIONS   IN  ACETIFICATION.  53 

This  is  now  accepted  as  an  approximate  explanation  of 
the  main  reactions  that  take  place  in  the  conversion  of 
alcohol  into  acetic  acid. 

The  relative  proportions  of  alcohol,  acet aldehyde  and 
acetic  acid  present  at  any  given  stage  of  the  process 
will  depend  to  a  large  extent  upon  the  conditions  of  the 
fermentation.  If  too  little  air  be  supplied  the  secondary 
oxidation  will  not  keep  pace  with  the  first  oxidation, 
and  a  pronounced  odour  of  acetaldehyde  will  be  per- 
ceptible in  the  air  issuing  from  the  acetifiers. 

Acetal. — Another  intermediate  product  formed  in  the 
oxidation  is  acetal,.  CH3 .  CH(OC2H5)2,  which  is  produced 
when  a  mixture  of  aldehyde  and  alcohol  is  heated  to  a 
temperature  of  about  100°  C. — 

CH3 .  COH  +  2C2H5 .  OH  =  CH3 .  CH(OC2H5)2, 

and  is  also  formed  in  small  quantity  through  the  heat 
of  the  acetic  fermentation.  It  is  probable  that  Dober- 
einer's  "  light  oxygen  ether  "  (supra)  was  a  mixture  of 
acetal  and  acetaldehyde,  and  that  his  "  heavy  oxygen 
ether/'  obtained  in  a  later  stage  of  the  distillation,  was 
acetal. 

It  was  shown  by  Kromer  and  Pinner  *  that  acetal 
was  slowly  formed  by  keeping  alcohol  and  acetaldehyde 
together  for  several  months  at  the  ordinary  temperature. 

Ethyl  Acetate. — In  addition  to  acetaldehyde  and 
acetal,  a  small  amount  of  ethyl  acetate  or  acetic  ether 
is  always  produced  in  the  acetic  fermentation  through 
the  combination  of  the  alcohol  with  the  acetic  acid — 

CH3 .  COOH  +  C2H5 .  OH  =  CH3 .  COOC2H5  +  H20. 

*Jahresber.  Chem.,  1869,  502. 


64   VINEGAR:  ITS  MANUFACTURE  AND  EXAMINATION. 

In  the  manufacturing  process  this  is  also  finally  oxi- 
dised to  acetic  acid,  so  that  the  finished  vinegar  leaving 
the  acetifiers  will  usually  be  quite  free  from  this  ester. 
Since,  however,  a  trace  of  alcohol  (about  0-5  per  cent.) 
is  usually  left  unoxidised,  slow  combination  takes  place 
subsequently  between  this  alcohol  and  the  acetic  acid, 
and  the  aroma  of  stored  vinegar  is  principally  due  to  the 
formation  of  ethyl  acetate. 

Other  Products. — Traces  of  other  alcohols,  esters,  and 
acids  are  also  formed  in  the  acetic  fermentation,  their 
nature  and  quantity  depending  upon  the  character  of 
the  non-alcoholic  constituents  (sugars,  dextrins,  acids, 
etc.)  in  the  alcoholic  wash.  For  example,  formic  acid 
is  found  in  wine- vinegars,  succinic  acid  in  grain  vinegars, 
and  fusel  oils  in  spirit  vinegars  ;  but  although  some  of 
these  compounds  may  influence  the  flavour  of  a  vinegar, 
they  are  without  practical  importance  in  the  fermenta- 
tion process. 

Boutroux  *  gave  a  description  of  the  action  of  the 
acetic  fermentation  upon  dextrose,  and  showed  that 
gluconic  acid  was  produced.  His  experiments  were 
repeated  by  Brown,  |  who  found  that  gluconic  acid  was 
the  sole  product  of  the  action  of  B.  aceti  on  dextrose. 
The  bacteria  were  unable  to  hydrolyse  cane  sugar,  but 
oxidised  mannitol,  with  the  formation  of  laevulose  as  the 
main  product. 

Brown's  f  B.  xylmus  ("  the  Vinegar-Plant ")  behaved 
in  a  similar  way,  but  had  also  the  property  of  forming 
cellulose  from  leevulose,  which  was  not  possessed  by  any 
other  acetic  bacteria  then  known  (cf.  p.  41).  This 

*  Cmnptes  Send.,  1880,  236. 
•\Journ.  Chem.  Soc.,  1886,  xlix.,  172. 


CHEMICAL   REACTIONS   IN   ACETIFICATION.  55 

cellulose  gave  all  the  reactions  of  ordinary  cellulose,  and 
on  hydrolysis  yielded  a  dextro-rotatory  sugar. 

In  this  connection  mention  may  be  made  of  the  action 
of  acetic  bacteria  upon  other  alcohols.  Both  B.  aceti 
and  B.  xylinus  (Brown)*  are  capable  of  oxidising  propyl 
alcohol  to  propionic  acid,  but  are  unable  to  attack  methyl 
or  amyl  alcohols.  Glycerol  is  oxidised  completely  into 
carbon  dioxide  and  water,  with  a  small  quantity  of  an 
unknown  acid,  while  glycol  is  converted  into  glycollic 
acid— 

CH2(OH)CH2(OH)  +  02  =  CH2(OH)COOH  +  H2O. 

Oxidation  of  the  Acetic  Acid. — It  has  long  been  known 
that  if  vinegar  was  left  too  long  in  the  acetifiers  its  strength 
gradually  decreased,  but  it  was  left  for  Pasteur  f  to  prove 
that  this  loss  of  acetic  acid  was  bound  up  with  the  life 
of  the  micro-organisms. 

He  showed  that  the  "  Mycoderma  aceti  "  would  develop 
upon  a  nutrient  medium  containing  acetic  acid  but  no 
alcohol,  and  that  the  air  in  the  flask  subsequently  con- 
tained a  large  proportion  of  carbon  dioxide  but  no  oxygen, 
while  the  whole  of  the  acetic  acid  had  disappeared. 

He  called  attention  to  the  analogy  between  this  slow 
process  of  combustion  and  the  respiration  of  living 
organisms,  and  concluded  that  in  the  absence  of  alcohol 
the  micro-organisms  were  capable  of  transferring  oxygen 
to  the  acetic  acid  and  of  converting  its  carbon  into  car- 
bonic acid. 

At  the  same  time  the  phenomena  are  also  susceptible 
of  the  explanation  that  the  oxidation  of  the  acetic  acid 
is  due  to  enzymic  action  carried  beyond  the  process  of 

*  Ibid.,  1887,  638.  t  Loc.  tit.,  p.  94. 


56     VINEGAR  :    ITS   MANUFACTURE  AND   EXAMINATION. 

the  acetification  of  the  alcohol,  and  that  the  carbon 
dioxide  is  not  due  to  respiration  of  micro-organisms,  but 
is  a  combustion  process  analogous  to  that  effected  by 
the  excessive  oxidation  of  alcohol  by  platinum  black. 

Oxidations  Effected  by  Platinum  Black. — The  analogy 
between  the  oxidations  effected  by  platinum  black  and 
acetic  bacteria  furnished  Liebig  with  one  of  his  principal 
weapons  against  the  vitalistic  theory  of  acetification. 
The  differences  between  the  two  processes,  however,  were 
demonstrated  in  1873  by  von  Knierem  and  A.  Mayer,* 
who  showed  that  the  conditions  were  not  in  any  way 
comparable,  although  the  final  products  might  be  the 
same.  For  example,  the  acetic  fermentation  could  not 
take  place  in  the  presence  of  more  than  10  to  12  per  cent, 
alcohol,  whereas  platinum  black  could  effect  the  oxida- 
tion of  alcohol  of  any  strength.  In  the  latter  case  the 
oxidation  was  promoted  by  increasing  the  temperature, 
whereas  the  acetic  fermentation  was  inhibited  by  tem- 
peratures exceeding  about  40°  C. 

It  was  also  pointed  out  by  these  chemists  that  the 
same  analogies  were  to  be  observed  between  other  fer- 
mentation processes  and  the  hydrolytic  decompositions 
effected  by  dilute  acids. 

For  example,  the  conversion  of  starch  into  sugars 
could  be  effected  either  by  diastatic  "  fermentation " 
or  by  the  action  of  dilute  acids.  Moreover,  other  chemical 
agents,  such  as  chromic  acid,  could  effect  the  oxidation 
of  alcohol  to  acetic  acid. 

*  Landw.  Versuchsstat.,  1873,  xvi.,  305. 


57 


CHAPTER  V. 
ACETIC  ACID. 

Radical  Vinegar— Acetous  Acid— Acetic  Acid  in  the  Pharmacopoeias- 
Anhydrous  Acetic  Acid — Glacial  Acetic  Acid — MANUFACTURE  OF 
ACETIC  ACID — from  Verdigris — from  Spirit  Vinegar — from  the  Distil- 
lation of  Wood — Pyroligneous  Acid — from  Acetate  of  Lime — CHEMICAL 
PROCESSES  OF  OXIDATION — Platinum  Black — Use  of  Ozone — Ozone 
in  Acetifiers — Newton's  Apparatus — Properties  of  Acetic  Acid. 

Radical  Vinegar. — Acetic  acid,  as  the  Latin  origin  of  its 
name  (acetum)  indicates,  is  the  acid  of  vinegar,  from 
which  it  was  first  separated  in  a  more  concentrated  form 
by  fractional  distillation,  neutralisation  with  alkali, 
crystallisation,  and  redistillation  of  the  salt  with  acid 
(see  p.  3). 

The  strongest  acid  thus  obtained  was  known  as  alkalised 
vinegar,  or  radical  vinegar,  which  Bailey's  English 
Dictionary  of  1747  defines  as  "  the  sharpest  Part  of 
Vinegar,  which  hath  its  Phlegm  *  drawn  off." 

In  the  London  Pharmacopoeias  of  1721,  1746,  and 
1788  ordinary  distilled  vinegar  (containing  about  6  per 
cent,  of  acetic  acid)  is  described  by  that  name  (Acetum 
distillatum) ,  but  this  was  changed  in  the  Pharmacopoeia 
of  1809  to  "  acetic  acid "'  (Acidum  aceticum),  and  to 
"  dilute  acetic  acid  "  (Acidum  aceticum  dilutum)  in  the 
Pharmacopoeia  of  1824. 

*  Water. 


58     VINEGAR  :    ITS   MANUFACTURE   AND   EXAMINATION. 

Acetous  Acid. — In  the  edition  of  1788  the  more  con- 
centrated acid  is  termed  "  acetous  acid "  (Acidum 
acetosum) — a  name  which  constantly  recurs  in  Acts  of 
Parliament  down  to  1844,  and  survives  in  the  term 
"  acetous  fermentation/'  which  is  still  used  in  the  vinegar 
industry.  This  name  was  given  to  the  acid  derived  from 
vinegar,  because  it  was  believed  to  contain  one  atom  less 
oxygen  in  its  molecule  than  acetic  acid  from  wood,  and 
the  salts  that  it  formed  with  alkalies  and  heavy  metals 
were  termed  acetites,  to  distinguish  them  from  acetates. 
The  name  originated  with  the  French  chemist  Berthollet, 
who  in  1785  published  a  paper  to  prove  that  the  acid 
obtained  by  distillation  of  verdigris  differed  in  its  pro- 
perties from  the  acetous  acid  derived  from  vinegar.  He 
regarded  the  acid  derived  from  the  salt  as  a  compound  of 
acetous  acid  with  oxygen. 

Even  as  late  as  1806,  we  find  the  first  edition  of  the 
Encylopcedia  Britannica  referring  to  "  acetous  acid  in 
that  concentrated  state  in  which  it  is  called  radical 
vinegar." 

In  1808  Henry  *  remarks,  with  reference  to  this  question, 
"  It  appears  that  acetic  acid  differs  only  from  the  acetous 
in  containing  less  water  and  more  mucilage/' 

Acetic  Acid  in  the  Pharmacopoeias.— It  was  probably 
owing  to  this  proof  of  identity  that  the  name  of  "  acetic 
acid  "  was  given  to  distilled  vinegar  in  the  Pharmacopoeia 
of  1809. 

In  the  next  edition  of  Phillip's  Translation  (1824)  it 
is  pointed  out  that  the  "  mucilage  "  f  which  passed  over 
and  condensed  with  the  acetic  acid  in  the  distillation  of 

*  Epitome  of  Chemistry,  1806,  p.  302. 

f  By  the  term  mucilage  was  understood  what  we  now  describe  as  "  extract." 


ACETIC   ACID.  59 

vinegar  rendered  it  difficult  to  obtain  pure  white  acetate 
of  potash  on  saturating  the  acid  with  alkali.  For  this 
reason  acetic  acid  derived  from  wood  was  introduced 
into  the  Materia  Medica  under  the  name  of  "  stronger 
acetic  acid  distilled  from  wood  "  (acidum  aceticum  fortius 
e  ligno  destillatum) .  At  that  time  the  strongest  acid 
known  had  a  specific  gravity  of  1-043,  and  contained 
about  32  per  cent,  of  acid,  or  five  times  as  much  as  dis- 
tilled vinegar. 

In  the  following  edition  of  Phillip's  Translation,  pub- 
lished in  1836,  this  "  stronger  acid  "  was  described  as 
"  acetic  acid  "  without  any  qualification,  and  was  stated 
to  contain  30-8  per  cent,  of  the  anhydrous  acetic  acid; 
while  glacial  acetic  acid,  the  strongest  acid  procurable, 
became  solid  at  about  40°  F.,  and  consisted  of  one 
equivalent  of  anhydrous  acetic  acid  and  one  equivalent 
of  water.  No  alteration  was  made  in  the  next  issue  in 
1851. 

In  the  first  edition  of  the  British  Pharmacopoeia,  pub- 
lished in  1867,  "  acetic  acid  "  was  prescribed  to  contain 
28  parts  of  "  anhydrous  acid/'  corresponding  to  33  parts 
by  weight  of  the  hydrated  acid.  This  corresponded  in 
strength  with  the  acetic  acid  of  commerce  and  the 
"  Purified  Pyroligneous  Acid  "  of  the  Dublin  Pharma- 
copoeia, but  was  not  so  strong  as  the  "  Acetic  Acid  "  of 
the  London  Pharmacopoeia  (supra).  It  was  much  weaker 
than  the  "Acetic  Acid  "  of  the  Edinburgh  Pharmacopoeia, 
which  contained  upwards  of  95  per  cent,  of  acid. 

Anhydrous  Acetic  Acid. — Considerable  confusion  has 
been  caused  through  the  belief  which  was  at  one  time 
generally  accepted,  that  acetic  acid  did  not  exist  in  the 
anhydrous  state,  and  was  only  known  in  combination 


60     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

with  water  or  a  base.  In  other  words,  the  compound 
we  now  describe  as  acetic  anhydride  was  formerly  re- 
garded as  the  hypothetical  acid.  "  Anhydrous  acetic 
acid/'  as  existing  in  dry  sodium  acetate,  was  assigned 
the  formula  C4H303,*  while  glacial  acetic  acid  was  re- 
garded as  a  monohydrated  acid,  C4H3O3,  HO,  crystal- 
lising at  45°  F.  The  hypothetical  anhydrous  acid  was 
also  known  as  acetylic  acid,  from  being  regarded  as  a 
compound  of  the  radical  acetyl,  C4H3,*  and  oxygen. 
This  use  of  the  term  radical  was  a  development  of  the 
idea  connoted  by  the  word  in  radical  vinegar  which  was 
in  use  long  before  the  discovery  of  oxygen. 

According  to  Nicholson, f  the  term  radical  was  used 
in  1823,  to  describe  "  the  distinguishing  part  of  an  acid, 
by  its  combination  with  the  oxygen  common  to  all  acids/' 
Thus  sulphur  was  the  radical  of  sulphurous  and  sulphuric 
acids. 

The  terms  "  dry  "  acetic  acid  and  "  real  "  acetic  acid 
were  used  as  synonyms  of  anhydrous  acetic  acid,  and 
this  must  be  borne  in  mind  in  calculating  the  strengths 
of  acetic  acid  mentioned  in  the  earlier  Pharmacopoeias. 
In  the  British  Pharmacopoeia  of  1867  reference  is  made 
to  both  acetic  acids,  and  to  prevent  mistake  the  chemical 
formulae  are  given,  showing  that  by  "  real "  acid  the 
anhydrous  compound  was  understood. 

In  the  Pharmacopoeia  of  1885,  however,  the  term 
"  real "  acid  is  used  to  describe  the  hydrated  acid, 
CH3 .  COOH,  thus  increasing  the  confusion  ;  but  in  the 
current  issue  all  ambiguity  has  been  avoided  by  the  use 
of  the  chemical  name  "  hydrogen  acetate/' 

*  Old  notation  :  C  =  6  ;   H  =  1  ;   0  =  8 

f  Dictionary  of  Chemistry,  1823. 


ACETIC   ACID.  61 

In  1874  the  Society  of  Public  Analysts  adopted  3  per 
cent,  of  "  real "  acetic  acid  as  the  minimum  limit  of 
strength  for  vinegar.  It  is  doubtful  whether  this  was 
intended  to  refer  to  the  anhydrous  acid  (acetic  anhydride) 
or  to  hydrogen  acetate.  Allen,  speaking  in  1893  on  the 
subject,*  was  not  certain  upon  the  point,  but  was  inclined 
to  believe  that  acetic  anhydride  was  meant. 

Glacial  Acetic  Acid. — The  most  concentrated  solutions 
of  acetic  acid  were  first  obtained  by  saturating  dry 
charcoal  with  vinegar,  and  distilling  the  mass.  Then, 
by  exposing  the  later  fractions  of  the  distillate  to  a 
freezing  mixture,  the  water  separated  as  ice,  while  a 
stronger  acid  could  be  drained  off  the  crystals.  Only  a 
relatively  weak  acid  could  be  thus  prepared,  and  prior 
to  the  introduction  of  wood  acid  all  concentrated  acid& 
were  prepared  by  dry  distillation  of  verdigris  or  copper 
acetate.  Acid  derived  in  the  first  instance  from  the  dis- 
tillation of  wood  soon  displaced  the  acid  of  higher  strength 
derived  from  vinegar. 

It  is  interesting  to  follow  in  the  successive  issues  of  the 
London  Pharmacopoeia  how  the  concentrated  acetic 
acid  of  commerce  became  purer  and  more  concentrated. 
In  Phillip's  Translation  of  1824  there  is  no  mention  of 
the  glacial  acid,  and  the  author  states  that  he  has  not 
met  with  acetic  acid  of  greater  strength  than  30  per 
cent.  In  the  next  edition  (1836)  there  is  a  reference 
to  glacial  acetic  acid,  "  so-called  from  becoming  crystal- 
line at  about  40°  F.,"  while  in  the  following  edition 
(1851)  the  solidification  point  is  given  as  45°  F.  In  the 
first  edition  of  the  British  Pharmacopoeia  (1867)  glacial 
acetic  acid  is  included  as  a  drug,  and  is  stated  ta 

*  Analyst,  1893,  xviii.,  183. 


62     VINEGAR  :    ITS    MANUFACTURE   AND    EXAMINATION. 

crystallise  at  34°  F.  and  remain  solid  until  the  tempera- 
ture reaches  48°  F.,  while  in  the  editions  of  1885  and  1898 
glacial  acetic  acid  is  required  to  have  a  specific  gravity, 
of  1-058,  and  to  remain  crystalline  above  60° F.  (15-5°  C.). 


MANUFACTURE   OF    ACETIC    ACID. 

The  earliest  method  of  preparing  a  strong  acetic  acid 
from  vinegar  has  already  been  mentioned  (p.  57).  Another 
process  of  concentration  was  to  freeze  the  stronger  frac- 
tions obtained  in  the  distillation  of  vinegar,  and  to 
separate  the  crystals  from  the  unfrozen  acid. 

Acetic  Acid  from  Verdigris. — But  the  chief  source  of 
acetic  acid  prior  to  the  discovery  of  pyroligneous  or  wood 
acid  was  copper  acetate,  which  was  popularly  known 
as  distilled  verdigris,  from  the  use  of  distilled  vinegar  in 
its  preparation.  This  salt  was  obtained  by  the  action  of 
a  crude  vinegar,  derived  from  refuse  grapes,  upon  plates 
of  copper.  These  were  placed  on  wooden  gratings,  which 
were  suspended  in  the  vinegar  for  about  three  weeks, 
after  which  they  were  removed,  exposed  to  the  air  for 
a  day  or  two,  and  again  immersed  in  the  vinegar.  In 
many  parts  of  France  each  farm  house  had  its  verdigris 
cellar,  where  all  wine  that  had  become  sour  was  thrown 
into  tubs  kept  for  the  purpose. 

As  soon  as  the  plates  had  become  sufficiently  coated 
with  the  crystals  the  acetate  was  scraped  off  and  sold 
in  its  moist  condition  to  the  dealers. 

This  salt  was  a  basic  acetate  with  a  composition  approxi- 
mating to  the  formula  (CH3C02)2Cu  .  CuO  .  6H20.  When 
it  was  dissolved  in  distilled  vinegar  and  the  solution 


ACETIC   ACID. 


63 


crystallised,  normal  cupric    acetate,   (CH3C02)2Cu  .  H2O, 
was  obtained. 

The  crystals  of  copper  acetate  were  known  to  the 
alchemists,  who  termed  them  Crystals  of  Venus,  and 
the  distilled  acetic  acid  or  radial  or  aromatic  vinegar  of 
the  apothecaries  was  derived  from  this  verdigris 
by  dry  distillation  in  a  stoneware  retort,  which  was 
gently  heated  in  a  suitable  furnace  (see  Fig.  17).  The 
acid  vapours  were  condensed  in  a  series  of  receivers,  the 
last  of  which  was  connected  by  means  of  a  Welter's 
tube  with  a  flask  partly  filled  with  distilled  vinegar. 


Fig.  17. — Apparatus  for  Distillation  of  Radical  Vinegar. 

When  vapours  were  no  longer  distilled,  and  the  receivers 
in  .the  basins  of  water  remained  cool  the  process  was 
finished.  The  acid  thus  obtained  was  of  a  green  colour 
from  the  traces  of  copper  acetate  carried  over  mechani- 
cally in  the  distillation.  It  was  purified  by  redistillation 
in  a  glass  retort  heated  in  a  sand  bath. 

About  a  fifth  of  the  available  acetic  acid  was  lost  in 
this  process  through  being  decomposed  by  the  heat. 
To  obviate  such  loss  the  verdigris  was  heated  with  a 
small  amount  of  sulphuric  acid ;  but  this  had  the  draw- 
back of  yielding  a  distillate  containing  sulphurous  acid, 


64    VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

while  lacking  the  pleasant  aroma  (the  so-called  pyro- 
acetic  spirit)  of  the  product  obtained  by  dry  distillation. 
Hence,  long  after  the  introduction  of  wood  acid,  the 
process  described  above  continued  in  use  for  the  manu- 
facture of  "  aromatic  vinegar/'  It  was  not  until  the 
method  of  purifying  wood  acid  had  been  perfected  that 
it  was  finally  superseded. 

Preparation  from  Spirit  Vinegar. — The  commercial  spirit 
vinegar  (Essig-sprit  or  Spritessig),  containing  about 
12  per  cent,  of  acetic  acid,  is  used  as  the  source  of  a 
concentrated  acetic  acid  of  about  80  per  cent,  strength, 
which  fetches  a  much  higher  price  than  acetic  acid  derived 
from  wood. 

Such  concentration  is  not  possible  simply  by  fractional 
distillation  in  an  ordinary  retort,  since  the  stronger 
fractions  which  pass  over  towards  the  end  of  the  dis- 
tillation are  contaminated  by  products  of  the  decomposi- 
tion of  extractive  matters  in  the  vinegar. 

To  obviate  this,  Stein  devised  a  method  of  raising  the 
boiling  point  of  the  vinegar  by  adding  to  it  about  one- 
third  of  its  weight  of  salt.  By  this  means  a  considerably 
larger  yield  of  acetic  acid  was  obtained,  though  a  large 
proportion  was  still  left  in  the  retort.  The  distillation 
was  carried  out  in  tin  or  copper  retorts. 

Although  a  much  stronger  product  than  the  original 
vinegar  was  obtained  in  this  way,  the  method  has  been 
superseded  by  the  process  of  neutralising  the  Essig- 
sprit  with  lime,  evaporating  the  liquid  to  dryness,  and 
distilling  the  crude  calcium  acetate  with  a  mineral  acid. 
The  distillate  has  a  specific  gravity  of  about  1  -060  (about 
49  per  cent.),  and  is  purified  by  further  distillation  with 
sodium  or  calcium  acetate. 


ACETIC    ACID.  65 

Acetic  Acid  from  Wood. — The  discovery  that  acetic  acid 
was  formed  in  the  dry  distillation  of  wood  appears  to 
date  back  no  further  than  the  middle  of  the  eighteenth 
century,  when  Glauber  described  a  "  wood  acid "  or 
pyroligneous  acid  as  one  of  the  constituents  of  the  dis- 
tillate, while  Boerhaave  pointed  out  that  this  acid  was 
closely  related  to  the  acid  of  vinegar.  Glacial  acetic  acid 
was  first  prepared  in  1793  by  Lowitz,  and  seven  years 
later  it  was  proved  by  Fourcroy  and  Vauquelin  that 
pyroligneous  acid  was  nothing  more  than  acetic  acid 
contaminated  with  other  products  of  the  distillation. 
It  was  owing  to  the  difficulty  of  completely  eliminating 
these  impurities  that  the  identity  of  wood  acetic  acid 
and  vinegar  "  acetous  "  acid  remained  unknown  for  so 
long  a  time. 

In  the  year  1799  the  first  plant  for  the  dry  distillation 
of  wood  on  a  manufacturing  scale  was  erected  by  Lebon, 
with  the  object  of  obtaining  charcoal,  pyroligneous  acid, 
tar,  and  gas  for  lighting  and  heating  purposes.  A  few 
years  later  a  factory  was  started  by  Stoltze  in  Halle  for 
obtaining  pyroligneous  acid  from  wood  and  converting 
it  into  pure  acetic  acid.  About  the  same  time  the  manu- 
facture was  begun  in  England,  and  in  1808  Mollerat 
was  distilling  wood  at  Pellerey  in  France,  and  converting 
the  acid  into  a  table  vinegar. 

An  outline  of  his  process  was  published  in  Paris,* 
with  reports  upon  the  products  by  Berthollet,  Fourcroy, 
and  Vauquelin.  It  was  stated  that  the  acid  there  pro- 
duced was  of  such  strength  that  when  diluted  with 

*  Memoires  sur  la  Distillation  du  Bois  et  1'Emploi  de  ses  Produits,  par 
J.  M.  Mollerat,  et  Rapports  faits  a  ce  Sujet  par  M.  M.  Berthollet,  Fourcroy 
et  Vauquelin,  Paris,  1808. 

5 


66     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

seven  parts  of  water  it  yielded  a  good  vinegar,  and  that 
it  was  identical  with  the  acid  obtained  by  the  distillation 
of  wine  vinegar. 

Pyroligneous  Acid. — The  crude  acid  first  separated  from 
the  products  of  the  distillation  is  a  yellowish-brown 
to  dark  brown  liquid  with  a  characteristic  tarry  odour. 
It  has  a  specific  gravity  ranging  from  about  1-020  to 
1-030,  and  contains  not  only  acetic  acid  but  also  small 
amounts  of  other  fatty  acids  (formic,  butyric,  valeric), 
together  with  esters,  alcohols  (e.g.,  furfural),  acetone, 
phenols,  and  tarry  products.  The  proportions  of  these 
constituents  vary  with  the  nature  of  the  wood,  tem- 
perature of  distillation,  and  method  of  condensing  the 
fractions. 

The  antiseptic  action  of  the  crude  acid  is  largely  due 
to  the  presence  of  the  phenols,  and  accounts  for  its  value 
as  an  agent  for  curing  hams  and  fish. 

After  removal  of  the  acetone  the  crude  pyroligneous 
acid  is  neutralised  with  lime,  and  the  liquid  evaporated 
to  obtain  crude  brown  acetate  of  lime.  Or  soda  is  used 
for  the  neutralisation  of  the  liquid,  which  is  then  con- 
centrated to  obtain  acetate  of  soda. 

These  impure  salts  are  sold  to  the  makers  of  acetic 
acid,  who  distil  them  with  hydrochloric  or  sulphuric 
acid,  to  separate  the  combined  acetic  acid. 

The  acid  derived  from  the  calcium  salt  is  known  com- 
mercially as  "  lime  acid/'  while  that  derived  from  sodium 
acetate  is  termed  "  soda  acid,"  and  fetches  a  higher 
price,  owing  to  its  usually  containing  less  impurities,  and 
thus  having  a  better  aroma. 

Acid  from  Acetate  of  Lime. — The  modern  process  of  dis- 
tilling acetic  acid  from  commercial  acetate  of  lime  may 


ACETIC   ACID.  67 

be  made  more  clear  by  the  following  outline  : — On  dis- 
tilling together  1  ton  of  acetate  of,  say,  65  per  cent, 
strength,  and  1  ton  of  hydrochloric  acid  of  30°  Tw., 
there  will  be  obtained  approximately — 

(a)  180  gallons  of  strong  acid  of  specific  gravity  1-057, 

say,  46  per  cent. ; 

(6)  100  gallons  of  feints  of  specific  gravity  1-020,  say, 
10  per  cent., 

corresponding  together  to  43  per  cent.  acid. 

The  strong  crude  acid  (a),  when  fractionated  in  a 
column  still,  taking  a  charge  of  about  250  gallons,  will 
yield  approximately— 

(1)  25  gallons  of  first  runnings,  used  in  the  manufacture 

of  white  lead. 

(2)  150  gallons  of  middle  fractions   (specific  gravity, 

1-045  to  1-050)  used  for  preparing  acid  (6). 

(3)  50  gallons  of  last  runnings  of  about  70  per  cent. 

strength. 

(4)  20  to  25  gallons  of  a  residue  of  acid,  tarry  matters, 

fatty  acids,  etc. 

The  feints  (b)  are  neutralised  with  soda,  evaporated, 
and  crystallised,  the  crystals  of  sodium  acetate  being 
separated  by  means  of  a  hydro-extractor,  and  used  for 
the  manufacture  of  the  best  "  soda  acid." 

The  fraction  (2)  is  redistilled,  after  treatment  with 
sulphuric  acid  and  potassium  permanganate  to  destroy  im- 
purities, the  middle  fractions  being  used  for  technical  acid. 

The  stronger  fraction  (3)  is  also  oxidised  in  the  still, 
together  with  the  similar  fractions  from  other  charges, 
and  is  redistilled  to  obtain  higher  strengths  (80  per  cent., 
to  glacial  acid). 


68    VINEGAR  :    ITS   MANUFACTURE   AND   EXAMINATION. 

In  each  case  the  first  oily  runnings  and  weaker  fractions 
are  separated,  and  worked  up  with  similar  fractions. 

CHEMICAL    PROCESSES    OF    OXIDATION. 

Oxidation  by  Means  of  Platinum  Black. — The  process 
of  catalytic  oxidation,  discovered  in  1835  by  Dobereiner 
(see  p.  52),  has  been  made  the  basis  of  several  indus- 
trial methods,  especially  in  Germany,  where  alcohol  is 
relatively  cheap. 

The  original  manufacturing  apparatus  of  Dobereiner 
consisted  of  a  glass  vessel  in  which  was  a  series  of  sup- 
ports at  different  levels.  On  each  of  these  were  several 
basins,  each  containing  a  tripod  holding  a  watch-glass 
filled  with  platinum  black.  A  current  of  air  was  drawn 
through  the  apparatus,  while  the  temperature  was  main- 
tained at  30°  to  35°  C.  by  means  of  a  steam  coil.  The 
vapours  of  the  evaporated  alcohol  came  into  contact  with 
the  oxygen,  and  under  the  influence  of  the  platinum  black 
acetic  acid  was  produced,  and  condensing  upon  the  walls 
of  the  vessel,  was  collected  in  a  receptacle  at  the  bottom. 

An  apparatus  with  a  capacity  of  about  700  litres, 
containing  about  200  to  210  grammes  of  platinum,  was 
capable  of  transforming  1  kilo,  of  pure  alcohol  into 
acetic  acid,  while  in  some  of  the  larger  apparatus  a  charge 
of  as  much  as  17  kilos,  of  platinum  black  was  employed 
to  convert  150  litres  of  alcohol  into  acetic  acid  per  day. 

In  practice  it  was  found  that  the  regulation  of  the 
exact  quantity  of  air  was  extremely  difficult.  If  too 
little  was  supplied  a  large  proportion  of  acetaldehyde 
and  acetal  was  produced,  while  by  increasing  the  current 
of  air  there  was  a  loss  of  acetic  acid  by  evaporation. 


ACETIC   ACID.  69 

A  much  more  important  drawback  was  that  after  a 
short  time  the  platinum  black  became  spent,  and  had 
to  be  re-calcined  to  render  it  active  again — a  process 
of  necessity  attended  with  the  loss  of  expensive  material. 

To  obviate  this  a  method  was  devised  in  which  the 
platinum  black  was  maintained  at  about  300°  C.  in  a 
porcelain  tube,  through  which  was  passed  a  current  of 
alcohol  vapours  mixed  with  air  or  oxygen. 

In  a  later  modification  of  the  process  the  platinum 
black  was  heated  to  incandescence  by  means  of  an  electric 
current. 

Use  of  Ozone. — In  the  year  1872  a  note  was  published 
by  Widemann  *  upon  the  use  of  ozone  in  the  manufacture 
of  vinegar.  The  process  described  consisted  in  causing 
the  alcoholic  liquid  to  fall  drop  by  drop  through  a  column 
containing  fragments  of  glass  or  porcelain,  and  to  meet 
on  its  way  a  current  of  hot  air  which  had  been  passed 
through  a  gas  flame.  The  action  of  this  hot  air  upon  the 
alcohol  was  claimed  to  effect  acetification. 

A  plant  to  work  the  process  upon  an  industrial  scale 
was  set  up  by  Widemann  in  America,  and  numerous 
modifications  of  the  process  were  patented. 

It  is  open  to  question  whether  simple  passage  of  air 
through  a  gas  flame  will  effect  ozonisation  of  the  oxygen. 
Moreover,  Claudon,f  who  repeated  the  experiment  with 
air  which  had  been  ozonised  in  the  usual  way,  was  unable 
to  obtain  similar  results.  The  expense  of  ozonisation 
would  also  be  a  factor  against  the  commercial  success 
of  any  such  process,  even  if  practicable. 

Ozone  in  Acetiflers. — By  a  curious  misapprehension  of 

*  Comptes  Eendust  1872. 

f  Fabrication  du  Vinaigre  (C.  Franche),  p.  188. 


70     VINEGAR  I    ITS   MANUFACTURE   AND    EXAMINATION. 

the  function  of  ozone  in  any  chemical  oxidation  of  alcohol, 
attempts  were  made,  especially  in  this  country,  to  accel- 
erate acetification  by  the  introduction  of  ozonised  air 
into  the  acetifiers. 

The  experiments  were  tried  on  a  large  scale  in  several 
of  the  largest  vinegar  works  in  London,  but  in  no  case 
did  they  prove  successful,  and  were  abandoned  after  a 
few  months'  trial. 

It  is  difficult  to  understand  the  theory  supposed  to 
underlie  this  use  of  ozone,  for  it  is  a  powerful  bactericidal 
agent,  and  would  thus  be  most  unlikely  to  promote  the 
growth  or  activity  of  acetic  bacteria. 

The  statements  put  forward  by  the  promoters  of  some 
of  these  processes  to  the  effect  that  the  Mycoderma  aceti 
developed  more  readily  in  the  presence  of  ozonised  air, 
as,  for  instance,  when  the  gyle  containing  it  was  projected 
in  a  fine  spray  into  a  chamber  of  such  air  (see  illustration, 
p.  71),  have  not  been  borne  out  by  the  results  of  prac- 
tical experience. 

Newton's  Apparatus. — In  the  apparatus  patented  by 
Newton  (Eng.  Pat.  1905,  1872)  the  use  of  ozone  or 
ozonised  air  "produced  by  passing  a  current  of  atmos- 
pheric air  through  a  flame "  was  claimed  for  effecting 
acetification. 

The  liquid  to  be  acetified  was  pumped  from  the  vessel 
N  in  the  form  of  a  fine  spray  into  the  chamber  A,  where 
it  meets  with  the  ozone  or  ozonised  air  drawn  or  forced 
by  means  of  the  pump,  K,  from  the  vessel  B.  A  series 
of  such  chambers  may  be  superposed,  the  liquid  leaving 
the  bottom  of  each  being  passed  in  a  fine  spray  into  the 
next  one  below. 

Properties  of  Acetic  Acid. — Pure  acetic  acid  is  a  colourless 


ACETIC   ACID. 


71 


liquid  with  a  characteristic  pungent  odour  of  vinegar. 
When  chilled  a  little  below  the  ordinary  temperature  it 
solidifies  to  a  crystalline  mass,  the  solidification  point 
depending  upon  the  strength  of  the  acid  (vide  infra). 
When  applied  to  the  skin  it  produces  blisters,  and  many 
fatal  accidents  have  been  caused  through  its  being 
inadvertently  swallowed. 


Fig.  18.— Newton's  Patent  Process. 

Although  an  organic  acid,  it  is  remarkably  stable,  and 
is  not  readily  attacked  by  oxidising  agents.  It  can  be 
decomposed  by  passing  its  vapour  through  a  tube  heated 
to  redness,  the  products  of  decomposition  including 
methane  and  acetone. 

Most  of  its  salts  are  soluble  in  water  ;  several  of  them 
are  of  commercial  importance.  This  aluminium  acetate 


72     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 


and  ferric  acetate  (red  liquor]  are  used  as  mordants  in 
dyeing,  while  verdigris  (q.v.)  and  emerald  green  (cupric 
aceto-arsenite)  form  the  basis  of  oil  pigments. 

Solidification  Point  of  Acetic  Acid. — The  determination 
of  the  freezing  point  of  glacial  acetic  acid  is  one  of  the 
most  reliable  methods  of  ascertaining  the  amount  of 
water  present,  as  was  first  pointed  out  by  Riidorff.*  He 
showed  that  acetic  acid  of  100  per  cent,  strength  solidified 
at  16-7°  C.,  and  that  with  each  slight  increase  of  water 
the  freezing  point  fell.  His  results,  which  are  given  in 
tabular  form  below,  did  not  go  below  mixtures  con- 
taining 20  per  cent,  of  water,  and  his  determinations 
were  afterwards  supplemented  by  Grimaux,t  who  ascer- 
tained the  freezing  points  of  mixtures  of  all  strengths, 
from  93  to  16  per  cent.,  and  gave  the  following  summary 
of  his  results  : — 

RUDORFF'S  TABLE  OF  SOLIDIFICATION  POINTS  OF  MIXTURES 
OF  ACETIC  ACID  AND  WATER.J 


100  Parts  of 

100  Parts 

100  Parts  of 

100  Parts 

Acetic  Acid 

contain 

Soliftcation 

Acetic  Acid 

contain 

Solidification 

mixed  with 

by 

Point. 

mixed  with 

by 

Point. 

Water. 

Weight. 

Water. 

Weight. 

0-0 

0-0 

+  16-7 

8-0 

7-407 

6-25 

0-5 

0-497 

15-65 

9-0 

8-257 

5-3 

1-0 

0-990 

14-8 

10-0 

9-090 

4-3 

1-5 

1-477 

14-0 

11-0               9-910 

3-6 

2-0 

1-961 

13-25 

12-0             10-774 

2-7 

3-0 

2-912 

11-95 

15-0 

13-043 

-0-2 

4-0 

3-846 

10-5 

18-0 

15-324 

2-6 

5-0 

4-761 

9-4 

21-0 

17-355 

5-1 

6-0 

5-660 

8-2 

24-0 

19-354 

7-4 

7-0 

6-542 

7-1 

*  Ber.  d.  d.  Chem.  Ges.,  1870,  iii.,  390. 
f  Comptes  Rendus,  1873,  Ixxvi.,  486. 
%  Ber.  d  d.  Chem.  Ges.,  1870,  iii.,  370. 


ACETIC   ACID. 


73 


GRIMAUX'S  TABLE  OF  SOLIDIFICATION  POINTS  OF 
MIXTURES  OF  ACETIC  ACID  AND  WATER.* 


Water. 

Acetic  Acid. 

Solidification 
Point. 

Water. 

Acetic  Acid. 

Solidification 
Point. 

Per  cent. 

Per  cent. 

°C. 

Per  cent. 

Per  cent. 

°C. 

7-31 

92-69 

+  5-3              56-54 

43-46 

-16-4 

13-25 

86-75 

-1-4              61-68 

38-2 

-14-8 

23-52 

76-48 

-11-6              69-23 

30-77 

-10-9 

31-18 

68-82 

-19-3              76-23 

23-77 

-  8-2 

33-56 

66-44 

-20-5              79-22 

20-78 

-  7-3 

38-14 

61-86 

-24-0              81-89 

18-11 

-  6-4 

44-50 

55-50 

-22-3              83-79 

16-21 

-  5-5 

49-38 

50-62 

-19-8 

If  these  results  are  plotted  in  a  curve  in  which  the 
ordinates  are  the  solidification  points  and  the  abscissae 
the  proportions  of  water,  it  will  be  found  that  the  lines 
connecting  the  temperatures  are  practically  straight, 
and  that  their  point  of  intersection,  showing  the  maximum 
lowering  of  temperature,  corresponds  to  the  mixture 
containing  about  37  per  cent,  of  water.  This  pro- 
bably indicates  the  formation  of  a  definite  hydrate, 
C2H4O2  -f  2H2O.  No  break  occurs  at  about  28  per  cent, 
of  water,  such  as  is  found  in  the  table  of  specific  gravities 
at  15°  C.,  where  possibly  the  presence  of  a  compound, 
C2H4O2  +  H20,  is  suggested. 

It  has  already  been  pointed  out  (p.  61)  that  the 
pharmacopceial  requirements  for  the  solidification  point 
of  glacial  acetic  acid  have  steadily  been  raised.  In  the 
edition  of  1898  glacial  acetic  acid  was  required  to 
contain  98-9  per  cent,  of  hydrogen  acetate  (by  titration), 
and  to  remain  solid  at  15-5°  C.  (60°  F.).  Now,  this  solidifi- 
cation point  corresponds  to  an  acid  containing  not  99  per 
*  Comptes  Rendus,  1873,  Ixxvi.,  486. 


74     VINEGAR  :    ITS    MANUFACTURE    AND    EXAMINATION. 


cent.,  but  nearly  99-5  per  cent.,  as  is  shown  in  RMorfFs 
table  (p.  72). 

In  the  new  Pharmacopoeia  (1914)  this  error  has  been 
corrected,  and  glacial  acid  (98- 9  per  cent.)  is  required  not  to 
re-melt  entirely  until  the  temperature  rises  above  14' 7°  C. 

The  point  is  of  considerable  importance  in  connection 
with  the  Customs  duties  in  certain  countries .  For  example , 
in  New  Zealand  all  glacial  acid  below  the  strength  of  that 
of  the  British  Pharmacopoeia  is  required  to  pay  an  excess 
duty  of  5d.  per  lb.,  which  is  considerably  more  than  the 
ordinary  duty. 

Since  the  strength  is  ascertained,  by  the  Customs 
officials,  simply  by  determining  the  freezing  point,  acid 
of  over  99  per  cent,  was,  prior  to  1914,  liable  to  rejection 
if  it  did  not  behave  like  acid  of  99-5  per  strength. 

This  anomaly  is  not  found  in  the  United  States  Pharma- 
copoeia, which  defines  glacial  acid  as  containing  99  per 
cent,  of  absolute  acid,  solidifying  below  15°  C.,  and 
becoming  fluid  again  at  about  15°  C. 

OPTICAL  REFRACTION  OF  SOLUTIONS  OF  ACETIC  ACTD 
AT  20°  C.  (Ftoy). 


Acetic  Acid. 

Refractive 
Index. 

Acetic  Acid. 

Refractive 
Index. 

Acetic  Acid. 

Refractive 
Index. 

Per  cent. 

Per  cent. 

Per  cent. 

5 

1-3358 

40 

1-3592 

75 

1-3755 

10 

1-3395 

45 

1-3622 

80 

1-3764 

15 

1-3431 

50 

1-3649 

85 

1-3769 

20 

1-3465 

55 

1-3674 

90 

1-3766 

25 

1-3497 

60 

1-3699 

95 

1-3749 

30 

1-3528 

65 

1-3723 

100 

1-3710 

35 

1-3560 

70 

1-3742 

Optical  Refraction. — The  refractive  index  of  acetic  acid 
shows  analogous  variations  according   to   the   strength. 


ACETIC   ACID. 


75 


As  is  seen  in  the  foregoing  table  of  results  by  Fery,  it 
increases  steadily  up  to  about  85  per  cent.,  where  a 
break  occurs  in  the  curve,  and  the  refraction  falls  to 
1-3710  at  20°  C. 

SPECIFIC  GRAVITY  OF  MIXTURES  OF  ACETIC  ACID  AND 
WATER  (Oudemanns)* 


Acetic  Acid. 

Specific 
Gravity  at 
15°  C. 

Acetic  Acid. 

Specific 
Gravity  at 
15°  C. 

Acetic  Acid. 

Specific 
Gravity  at 
15°  C. 

Per  cent. 

Per  cent. 

' 

Per  cent. 

100 

1-0553 

66 

1-0717 

32 

1-0436 

99 

1-0580 

65 

1-0712 

31 

1-0424 

98 

1-0604 

64 

1-0707 

30 

1-0412 

97 

1-0625 

63 

1-0702 

29 

1-0400 

96 

1-0644 

62 

1-0697 

.  28 

1-0388 

95 

1-0660 

61 

1-0691 

27 

1-0375 

94 

1-0674 

60 

1-0685 

26 

1-0363 

93 

1-0686 

59 

1-0679 

25 

1-0350 

92 

1-0696 

58 

1-0673 

24 

1-0337 

91 

1-0705 

57 

1-0666 

23 

•0324 

90 

1-0713 

56 

1-0660 

22 

•0311 

89 

1-0720 

55 

1-0653 

21 

•0298 

88 

1-0726 

54 

•0646 

20 

•0284 

87 

•0731 

53 

•0638 

19 

•0270 

86 

•0736 

52 

•0631 

18 

•0256 

85 

•0739 

51 

•0623 

17 

•0242 

84 

•0742 

50 

•0615 

16 

•0228 

83 

•0744 

49 

•0607 

15 

1-0214 

82 

1-0746 

48 

•0598 

14 

1-0200 

81 

1-0747 

47 

•0589 

13 

1-0185 

80 

1-0748 

46 

•0580 

12 

1-0171 

79 

1-0748 

45 

•0571 

11 

1-0157 

78 

1-0748 

44 

•0562 

10 

1-0142 

77 

1-0748 

43 

•0552 

9 

1-0127 

76 

1-0747 

42 

•0543 

8 

1-0113 

75 

1-0746 

41 

•0533 

7 

1-0098 

74 

1-0744 

40 

•0523 

6 

1-0083 

73 

1-0742 

39 

•0513 

5 

1-0067 

72 

1-0740 

38 

•0502 

4 

1-0052 

71 

1-0737 

37 

1-0492 

3 

1-0037 

70 

1-0733 

36 

1-0481 

2 

1-0022 

69 

1-0729 

35 

1-0470 

1 

1-0007 

68 

1-0725 

34 

1-0459 

0 

0-9992 

67 

1-0721 

33 

1-0447 

*  Jahresber.  Fortschritte  der  Chemie,  1886,  p.  302. 


76     VINEGAR  :    ITS    MANUFACTURE   AND    EXAMINATION. 


Specific  Gravity. — Tables  of  the  specific  gravity  of 
mixtures  of  acetic  acid  and  water  of  different  strength 
have  been  published  by  Mohr  and  by  Oudemanns  (supra), 
but  these  differ  considerably  from  each  other,  possibly 
owing  to  the  presence  of  traces  of  higher  acids  as  impuri- 
ties in  the  acetic  acids  used  for  the  determinations. 

For  acids  of  strengths  of  25  to  40  per  cent,  a  deter- 
mination of  the  specific  gravity  is  useful  as  a  rough 
estimate  of  the  strength,  but  many  of  the  acids  of  80  per 
strength  upon  the  market  do  not  comply  with  the  specific 
gravity  given  in  the  tables. 

The  tables  agree  more  nearly  for  the  lower  strengths 
up  to  10  per  cent. 

BOILING  POINT  OF  GLACIAL  ACETIC  ACID  UNDER 
VARIOUS  PRESSURES  (Landolt). 


Pressure. 

Boiling 
Point. 

Pressure. 

Boiling 

Point, 

Pressure. 

Boiling 
Point. 

mm. 

°C. 

mm. 

°C. 

mm. 

6C. 

1,160 

132 

560 

109 

60 

48 

960 

126 

360 

96 

30 

31 

700 

119 

160 

73 

77 


CHAPTER  VI. 
PREPARATION   OF  THE   GYLE. 

The  Mash -Tun — Mashing  Machines — Hot  Liquor  Backs — Process  of  Mashing 
— Gelatinised  Grain — Addition  of  Sugar — The  Conversion  Process — 
Fermentation  of  the  Wort — Storing  the  Gyle. 

THE  first  step  in  the  manufacture  of  vinegar  is  the  pre- 
paration of  an  alcoholic  wash,  containing  also  sufficient 
nutriment  for  the  acetic  bacteria. 

In  the  production  of  spirit  vinegar  in  France  and 
Germany  a  diluted  spirit  derived  from  potatoes  or  maize 
starch  is  mixed  with  a  small  proportion  of  phosphates 
and  ammonium  salts,  and  used  for  the  purpose.  Wine 
vinegar  is  made  from  diluted  wine,  and  cider  vinegar  from 
sour  cider  or  from  apple  juice  expressed  for  the  purpose. 
Any  substance  capable  of  fermentation  so  as  to  yield 
an  alcoholic  liquor  is  also  capable  of  acetification  under 
suitable  conditions,  but  in  this  country  the  bulk  of  the 
vinegar  is  manufactured  from  malted  or  unmalted  grain, 
or  from  a  mixture  of  cereals  and  fermentable  sugars. 

The  malt  or  malt  and  grain  is  infused  in  a  mash-tun  or 
saccharified  in  a  "  converter  "  by  means  of  a  dilute  acid, 
and  the  gyle  thus  obtained  is  clarified  and  acetified  as 
subsequently  described. 

The  Mash-Tun. — The  most  important  piece  of  apparatus 
common  to  the  brewer  and  the  vinegar  maker  is  the 


78    VINEGAR:  ITS  MANUFACTURE  AND  EXAMINATION. 

mash-tun.  As  the  vinegar  manufacture  has  lagged 
behind  the  brewing  industry,  the  old-fashioned  plant  of 
fifty  years  ago  may  still  be  found  in  some  vinegar  works. 


8 


PREPARATION    OF   THE    GYLE. 


79 


For  example,  an  open  mash- tun,  like  that  shown  in 
the  accompanying  illustration  (Fig.  19),  in  which  the 
revolving  rakes  travelled  round  the  tun  by  engaging  in 
teeth  upon  the  circumference,  has  been  seen  by  the  writer 
in  old  vinegar  breweries. 

This  type  of  mash-tun  had  superseded  the  still  earlier 
form  in  which  the  crushed  malt  and  hot  water  were 


Fig.  20. — Section  of  Mash-Tun. 

stirred  together  by  long  poles  termed  "  oars."  In  up- 
to-date  vinegar  works  the  mash-tun  is  completely  closed 
in  with  non-conducting  material,  to  prevent  loss  of  heat, 
and  it  is  fed  by  a  mashing  machine  from  a  hot  liquor 
back  and  grist  case. 

The  copper  which  supplied  the  older  mash-tun  has,  in 
many  instances,  been  retained  for  heating  the  water  for 


80      VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 


the  first  mash,  but  the  stokehole  has  been  abolished,  and 
its  place  taken  by  a  steam  pipe. 

The  most  suitable  form  of  mash-tun  for  vinegar  brewing- 
is  one  provided  with  rakes,  and 
also  with  a  steam  coil  beneath 
the  perforated  false  bottom,  to 
enable  the  temperature  of  the 
mash  to  be  raised  gradually  from 
a  relatively  low  temperature. 

For  the  reasons  given  below, 
this  is  much  more  satisfactory 
than  raising  the  temperature 
suddenly  by  means  of  "  under- 
letting/' as  is  usually  done  in 
mashing  malt  for  beer. 

Otherwise  the  construction  of 
the  mash-tun  is  the  same  as  in  a 
brewery  (where  it  is  exceptional 
to  find  mash- tuns  with  coils),  and 
has  the  appearance  in  vertical 
section  shown  in  Fig.  20. 

The  steam  coil  would  be  fixed 
in  the  space  C  beneath  the  per- 
forated plates. 

The  sparge  is  an  essential  part 
of  the  plant  in  a  modern  vinegar 
brewery.  As  shown  in  the 
diagram  (Fig.  21),  it  consists  of 
a  cylindrical  box  or  "  basin/' 
communicating  at  the  bottom 
with  two  arms,  and  is  made  to  revolve  easily  about  a 
central  axis. 


PREPARATION    OF   THE   GYLE. 


81 


The  hot  water  coming  from  the  copper  enters  the  two 
arms,  which  are  perforated  at  regular  intervals  on  one 
side,  and  by  its  pressure  as  it  escapes  from  the  holes 
causes  the  sparge  to  rotate  and  to  sprinkle  the  upper 
surface  of  the  mash  with  an  evenly  distributed  shower. 

Mashing  Machines. — The  use  of  an  external  mashing 
machine  is  particularly  suitable  for  brewing  the  wort 
for  vinegar,  since  it  enables  a  more  thorough  and  even 
admixture  of  the  grain  and  hot  liquor  at  any  desired 
temperature  for  the  initial  mash  to  be  made  than  is 
possible  in  the  mash-tun  itself. 


Fig.  22. — Section  of  External  Mashing  Machine. 

The  first  machine  of  this  type  was  invented  in  1853  by 
Steel,  and  in  all  essentials  is  the  same  as  the  mashing 
machines  still  most  frequently  in  use. 

As  is  shown  in  the  section  (Fig.  22),  it  consists  of  a 
shaft  B  with  rakes  and  arms  at  right  angles,  revolving 
in  a  horizontal  cylinder  of  copper  or  iron  A. 

The  screw  propeller  H  is  a  modern  addition,  and  was 
not  present  in  the  original  machine.  The  shaft  is  made 
to  revolve  by  means  of  a  strap  over  the  wheel  D,  at  a 

6 


82     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

speed  of  150  to  180  revolutions  per  minute,  and  thus 
causes  a  very  rapid  admixture  of  the  hot  water,  which 
enters  by  a  pipe  at  E  with  the  grist  which  comes  from  the 
grist  case  through  a  shutter  F,  the  movement  of  which  is 
controlled  by  the  wheel  G. 

In  another  type  of  mashing  machine  the  agitators  are 
eliminated.  Thus,  in  Maitland's  machine,  the  grist  is 
delivered  in  a  steady  stream  into  a  cylinder  with  per- 
forated walls.  This  is  surrounded  by  another  cylinder, 
into  which  the  hot  water  is  forced,  and  is  thence  drawn 
in  a  series  of  fine  jets  through  the  perforations.  At  the 
bottom  of  the  cylinder  a  larger  jet  of  hot  liquor  is  forced 
upwards,  and  meeting  the  falling  grist,  completes  the 
admixture. 

Hot  Liquor  Backs. — The  use  of  coppers  for  heating 
the  water  for  mashing  has  been  superseded  in  most 
vinegar  works  by  a  hot  liquor  back,  which  is  fixed  at  a 
level  above  the  mash-tun,  and  is  connected  with  the 
mashing  machine,  and  also  with  the  underletting  pipe. 
This  back  is  usually  in  rectangular  form,  and  is  generally 
made  of  iron  cased  in  with  non-conducting  material  to 
prevent  loss  of  heat. 

The  liquid  is  most  conveniently  heated  by  means  of  a 
steam  pipe  delivering  steam  into  the  back,  and  if  care 
be  taken  to  prevent  oil  or  impurities  from  the  boiler 
gaining  admission  to  the  water,  this  method  is  quite 
satisfactory. 

Where,  however,  impurities  are  likely  to  be  carried 
over  with  the  steam,  it  is  preferable  to  heat  the  water 
by  means  of  a  copper  coil.  The  steam  entering  thus 
parts  with  its  heat,  and  is  condensed,  and  the  water 
escapes  through  a  trap  at  the  end  of  the  coil. 


PREPARATION    OF   THE    GYLE.  83 

The  temperature  of  the  water  in  the  back  is  indicated 
by  a  special  thermometer,  which  is  bent  at  right  angles 
and  fixed  in  an  opening  in  the  side  of  the  back.  As  a 
rule,  there  is  also  a  gauge  tube  outside  the  back  to  show 
the  height  of  the  water  within.  Or,  in  some  breweries, 
a  float  attached  to  a  cord  passing  over  pulleys  serves 
this  purpose,  the  amount  of  liquor  being  indicated  by 
the  position  of  a  counterweight  at  the  other  end  of  the 
cord,  in  relation  to  a  scale. 

Process  of  Mashing. — The  first  stage  in  the  preparation 
of  a  malt  or  grain  vinegar  is  in  all  essentials  the  same 
as  in  a  distillery.  In  each  case  the  object  is  to  obtain 
as  high  a  proportion  as  practicable  of  sugars  in  a  fer- 
mentable form. 

In  this  respect  the  mashing  process  differs  from  that  used 
in  the  brewing  of  beer,  where,  since  the  aim  is  to  leave 
a  relatively  large  proportion  of  unfermentable  dextrins, 
a  considerably  higher  mashing  temperature  is  per- 
missible. .  *  --, 

The  vinegar  brewer,  like  the  distiller,  must  mash  his 
malt  or  malt  and  grain  at  a  lower  temperature,  and  the 
boiling  of  the  wort  practised  by  the  brewer  is  usually 
unsuitable  for  his  purpose. 

If  he  is  using  a  mixture  of  malted  and  unmalted  grain, 
he  will  require  a  malt  of  good  diastatic  power,  but  when 
malted  barley  is  being  used  alone  a  malt  of  low  diastatic 
power  (say  about  30)  will  give  good  results. 

The  malt  or  mixture  of  malt  and  grain  is  crushed  in 
exactly  the  same  way  as  in  a  brewery,  and  is  then  passed 
through  a  Steel's  mashing  machine  into  the  mash-tun, 
with  the  calculated  quantity  of  water  to  give  a  mash 
at  a  temperature  of  about  120°  F. 


84     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION, 


PREPARATION    OF   THE    GYLE.  85 

The  temperature  is  then  very  slowly  raised,  either  by 
underletting  water  at  a  higher  temperature  or,  preferably, 
by  means  of  a  steam  coil  at  the  bottom  of  the  mash-tun. 

In  this  connection  it  is  of  practical  interest  to  note 
that  in  the  writer's  experience  naked  steam  may  be 
admitted  at  this  stage  into  the  mash- tun,  without  any 
appreciable  injury  to  the  diastase  of  the  malt.  After 
the  temperature  has  in  this  way  been  gradually  brought 
up  to  about  152°  F.,  while  the  goods  have  meanwhile 
been  kept  in  constant  movement  by  the  rakes  in  the 
tun,  the  mashing  is  continued  until  the  liquid  no  longer 
gives  a  blue  coloration  with  iodine. 

This  infusion  is  then  drained  off  and  a  second  mash 
of  an  hour  is  given  with  a  smaller  quantity  of  water 
at  155°  F.,  this  extract  being  drained  off  as  before.  Finally 
the  goods  in  the  tun  are  washed  from  above  with  water 
at  155°  F.,  which  is  distributed  over  their  surface  from 
the  arms  of  a  revolving  sparge. 

The  united  extracts,  which  will  have  a  specific  gravity 
of  about  1-060  (from  45  quarters  of  malt),  are  cooled 
to  about  70°  F.  by  means  of  refrigerators,  and  are  then 
fermented  with  yeast  as  described  subsequently. 

A  wort  obtained  in  this  way  is  readily  fermentable, 
but  the  use  of  low-dried  diastatic  malts  and  low  tem- 
peratures for  mashing  has  the  drawback  of  yielding 
vinegars  which  are  sometimes  very  difficult  to  free  from 
a  slight  degree  of  cloudiness.  This  turbidity  appears 
to  be  partly  due  to  albuminous  substances,  which  can  be 
coagulated  by  heat ;  for  boiling  the  worts  enables  them 
to  be  filtered  with  much  more  ease. 

As  a  rule,  however,  it  is  not  practicable  for  the  vinegar 
maker  to  boil  his  worts,  since  by  so  doing  he  converts 


86     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

dextrins  into  an  unfermentable  form,  and  thus  reduces 
his  yield  of  alcohol,  and  subsequently  of  acetic  acid. 

In  practice,  therefore,  it  is  advisable  to  use  a  malt  that 
has  been  dried  at  a  medium  temperature.  This  will  give 
a  wort  which,  while  fermenting  well,  although  not  giving 
the  highest  yield  of  alcohol,  will  yield  a  vinegar  which 
can  be  made  "  bright  "  without  much  difficulty. 

A  further  objection  to  the  production  of  an  infusion 
containing  the  largest  possible  proportion  of  fermentable 
sugar  is  that  the  vinegar  prepared  from  such  a  wort  will 
contain  very  little  solid  matter,  and  that  there  will, 
therefore,  be  a  possibility  of  its  being  condemned  as  an 
adulterated  article  under  the  Food  and  Drugs  Act. 

Gelatinised  Grain. — By  submitting  the  grain  to  a 
preliminary  heating,  the  starch  granules  swell  up  and 
become  gelatinised,  and  are  then  much  more  readily 
attacked  and  dissolved  by  the  diastase  of  malt. 

For  this  reason  it  is  possible  to  use  a  much  larger 
proportion  of  grain  of  this  description  than  of  ordinary 
untreated  or  "  raw  "  grain,  with  the  malt  in  the  mash- 
tun,  or  to  use  a  malt  of  much  lower  diastatic  power. 

Torrefied  or  "  popped  "  barley  is  one  of  these  products. 
It  is  prepared  by  heating  the  barley  until  the  starch 
granules  are  ruptured  and  the  grain  is  slightly  roasted. 
In  the  process  of  roasting  the  moisture  of  the  barley  is 
reduced  to  about  3  to  4  per  cent.,  while  the  fat  is  lowered 
by  about  50  per  cent.,  both  of  which  changes  are  advan- 
tageous from  the  brewing  point  of  view. 

Flaked  Maize  and  Rice. — As  the  large  amount  of  oil 
in  the  maize  is  of  no  use  to  the  brewer,  preparations 
known  as  "flaked  maize"  or  "flaked  maize  malt"  are 
sold  in  large  quantities. 


PREPARATION   OF  THE   GYLE.  87 

They  are  prepared  by  crushing  the  maize,  removing 
the  germ  containing  the  bulk  of  the  oil,  and  gelatinising 
the  starch  by  heat.  To  some  extent  the  heating  does 
the  work  of  diastase,  and  for  this  reason  such  products 
have  become  known  as  "  malts  "  in  the  brewing  industry. 

Flaked  rice  is  prepared  in  a  similar  manner,  but  in  that 
case  the  process  is  not  so  advantageous  to  good  mashing, 
since  rice  contains  much  less  oil  than  maize. 

Analyses  of  gelatinised  grains  are  given  in  Chap.  X,  and 
show  the  influence  of  the  processes  upon  the  composition 
of  the  cereals. 

In  some  vinegar  breweries  rice  or  maize  grits  are 
partially  gelatinised  on  the  spot  by  subjecting  them  to 
the  action  of  steam  under  pressure.  This  ruptures  the 
starch  granules,  converting  the  whole  mass  into  a  paste, 
which,  when  cooled  to  about  130°  to  140°  F.,  is  rapidly 
liquefied  on  the  addition  of  a  small  amount  of  crushed 
malt.  It  can  then  be  run  into  the  mash-tun,  where  the 
saccharification  of  the  starch  is  completed  at  the  same 
time  as  the  rest  of  the  mash.  In  this  way  a  large  quantity 
of  raw  grain  can  be  introduced  into  the  mash-tun,  without 
any  risk  of  finding  unconverted  starch  in  the  wort. 

This  entails  the  use  of  a  separate  vessel  or  "  converter  " 
for  the  gelatinisation  of  the  starch  of  the  raw  grain,  but 
by  suitable  manipulation  and  saccharification  in  stages 
it  is  possible  to  use  the  mash-tun  itself  for  the  purpose. 

For  example,  a  mixture  of  the  crushed  barley  and  malt 
is  slowly  heated  from  about  130°  to  about  170°  F.  The 
sugar  formed  in  the  hydrolysis  at  the  lower  temperatures 
protects  the  diastase  for  some  time  at  the  higher  tem- 
perature, so  that  a  considerable  amount  of  the  starch 
in  the  raw  grain  is  converted.  The  temperature  is  then 


88     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

raised  to  over  200°  F.,  and  kept  at  that  point  for  about 
30  minutes  to  gelatinise  the  starch,  after  which  the  mash 
is  cooled  to  130°  to  135°  C.  by  means  of  a  coil,  and  a  fresh 
portion  of  ground  malt  added  to  complete  the  hydrolysis 
of  the  gelatinised  starch.  When  now  the  temperature  is 
gradually  raised  to  155°  F.,  the  conversion  is  rapidly 
completed,  and  the  wort  is  then  drawn  off,  and  the 
"  goods  "  sparged  in  the  usual  way. 

Addition  of  Sugar. — Certain  makers  of  vinegars  prefer 
to  buy  the  products  of  the  acid  hydrolysis  of  cereal  starch 
in  the  form  of  ready-made  glucose,  which  is  sold  either 
in  the  form  of  a  thick  syrup  or  as  a  solid. 

A  suitable  proportion  of  the  sugar  is  added  to  the  wort 
as  it  leaves  the  mash- tun,  and  a  much  more  concentrated 
wash  can  thus  be  prepared  without  the  necessity  of  using 
larger  plant. 

Worts  to  which  commercial  glucose  has  been  added 
usually  "  attenuate  "  very  far,  and  hence  in  some  cases 
yield  a  vinegar  deficient  in  "  body/'  To  prevent  the 
product  being  too  thin  in  this  respect  special  preparations 
containing  unfermentable  dextrins  are  sometimes  used, 
or  a  certain  proportion  of  molasses  may  be  mixed  with 
the  glucose. 

In  several  of  the  larger  vinegar  breweries  a  "  converter  " 
is  used  for  transforming  the  starch  of  the  cereal  into 
fermentable  sugar,  and  thus,  while  obtaining  all  the 
advantages  of  a  product  prepared  by  acid  hydrolysis, 
they  also  retain  the  other  constituents  of  the  grain  (the 
nitrogenous  compounds  and  phosphoric  acid),  which  are 
not  present  in  commercial  glucose. 

The  Conversion  Process. — Instead  of  the  starch  of 
cereals  being  saccharified  by  the  diastase  of  malt,  a  process 


PREPARATION   OF  THE   GYLE.  89 

in  which  a  dilute  mineral  acid  is  used  as  the  hydrolytic 
agent  is  employed. 

Maize  or  rice  are  the  chief  materials  used  by  those  who 
prepare  their  worts  in  this  way,  and  when  malt  is  also 
added,  as  is  sometimes  the  case,  the  object  of  the  addition 
is  to  give  a  malt  flavour  to  the  product  or  to  make  it 
answer  more  closely  to  the  normal  composition  of  a 
barley  malt  vinegar. 

In  converting  the  starch  into  fermentable  dextrose,  the 
grain  is  mixed  with  dilute  sulphuric  acid  (about  3  per 
cent,  strength)  in  a  closed  iron  vessel,  where  it  is  heated 
for  several  hours  by  steam  under  pressure  until  a  sample 
of  the  liquid  no  longer  gives  a  reaction  for  unconverted 
starch. 

The  contents  of  the  converter,  which  now  consist 
largely  of  an  acid  solution  of  dextrose,  are  neutralised 
with  lime  and  chalk,  which  precipitate  the  sulphuric 
acid  as  gypsum,  and  are  then  drawn  off,  cooled,  and 
fermented  in  the  same  way  as  the  wort  obtained  by 
mashing. 

A  converter  of  average  size  will  take  a  charge  of  6  to 
7  tons  of  grain,  and  the  whole  of  the  starch  will  be  hydro- 
lysed  within  about  three  hours,  when  heated  with  steam 
under  a  pressure  of  about  10  Ibs.  After  neutralisation 
the  mixture  is  allowed  to  stand  for  several  hours  for  the 
calcium  sulphate  to  subside,  and  is  then  drawn  off  through 
filters,  cooled,  and  passed  into  the  fermenting  tuns. 

As  it  leaves  the  filters  the  wort  (from  the  above-men- 
tioned quantity  of  grain)  will  show  a  specific  gravity  of 
about  1  -070,  and,  if  a  strong  vinegar  is  required,  is  pitched 
with  yeast  directly  without  any  dilution.  It  is  more 
usual,  however,  for  the  liquid  to  be  diluted  with  water 


90     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

to     a     specific      gravity     of      1-055     to     1-060     before 
fermentation. 

Although  the  bulk  of  the  calcium  sulphate  separates 
in  insoluble  form  during  the  neutralisation,  a  considerable 
proportion  will  still  remain  in  solution,  and  will  afford 
an  indication,  though  not  an  infallible  one,  that  the 
vinegar  has  been  prepared  by  a  conversion  process. 


Fig.  24.— Underback  and  Refrigerator  (A.D.  1812). 

Usually  the  glucose  solution  derived  from  the  acid 
hydrolysis  of  grain  is  readily  fermentable,  and  a  wort 
of  specific  gravity  1-060  can  be  attenuated  without 
difficulty  down  to  a  specific  gravity  of  1-004  to  1-005. 
Vinegars  prepared  from  the  products  of  the  "  converter  " 
are  frequently  sold  as  "  malt  vinegar/'  although  they 
do  not  comply  with  the  definition  suggested  by  the 


PREPARATION   OF  THE   GYLE.  91 

Local  Government  Board,  which  requires  the  starch  to 
have  been  saccharified  by  the  diastase  of  malt. 

Fermentation  of  the  Wort. — After  leaving  the  mash-tun 
the  wort,  including  the  spargings,  is  pumped  through 
a  refrigerator  to  cool  it  down  sufficiently  for  the  addition 
of  the  yeast. 

In  the  older  vinegar  breweries  cooling  was  effected  by 
exposing  the  liquid  to  the  air  in  large  shallow  tanks, 
known  as  coolers,  such  as  that  shown  in  Fig.  24, 
which  represents  the  obsolete  plant  used  in  1812  in 
Messrs.  Beaufoy  &  Co.'s  Works.  But  at  the  present  day 
the  same  course  is  followed  as  in  breweries,  and  the  wort 
is  cooled  by  means  of  refrigerators,  which  are  usually 
of  the  vertical  type. 

As  is  shown  in  Fig.  25,  the  refrigerator  consists  essen- 
tially of  a  series  of  superposed  tubes,  through  which 
passes  a  current  of  cold  water.  The  wort  is  pumped 
into  a  trough  above  these  and  trickles  through  holes  in 
the  bottom  of  this  in  a  number  of  thin  streams  over 
the  tubes,  in  succession,  until  it  reaches  the  large  trough 
in  which  the  apparatus  stands. 

The  cooling  tubes  are  frequently  of  oval  instead  of 
circular  form,  so  as  to  offer  a  larger  cooling  surface  to 
the  liquid  trickling  over  them. 

Horizontal  refrigerators  (Fig.  27)  are  sometimes  em- 
ployed where  there  is  insufficient  height  for  the  other 
type,  and  when  the  supply  of  water  is  plentiful.  They 
are  made  in  the  form  of  a  rectangular  trough  with 
partitions  at  intervals.  In  each  compartment  is  a  hori- 
zontal tube  with  rounded  ends,  through  which  passes 
the  cold  water.  The  hot  wort  passes  successively 
through  these  compartments,  and  is  thus  cooled  in 


92     VINEGAR  I    ITS   MANUFACTURE   AND    EXAMINATION. 


To  face  p.  93.] 


Fig.  26.— Exterior  of  Fermenting  Tuns. 


PREPARATION    OF   THE    GYLE. 


93 


stages  before  running  into  the  main  leading  to  the 
fermenting  tun. 

Except  in  cases  where  a  good  growth  of  yeast  is  the 
primary  object,  it  is  unnecessary  to  cool  the  wort  for 
vinegar  to  so  low  a  temperature  as  is  required  for  beer. 

Yeast  may  be  added  to  the  wort  at  a  temperature  of 
70°  to  75°  F.,  and  although  a  "  boiling  fermentation  " 
usually  follows,  the  attenuation  takes  place  more  rapidly 
and  completely  than  when  lower  temperatures  are  main- 
tained. The  temperature  rapidly  rises,  and  on  the  second 


V/AUR    OUttfb 


Fig.  27. — Horizontal  Refrigerator. 

day  will  be  as  high  as  90°  to  93°  F.,  falling  on  the  third 
day  to  about  85°  F.,  while  the  yeast  working  under  such 
conditions  produces  very  little  "  head." 

In  some  vinegar  factories  the  production  of  yeast  is 
the  main  end  in  view,  while  vinegar  is  only  manufactured 
as  a  by-product.  In  such  cases  the  conditions  to  be 
followed  are  quite  different  from  those  described  above. 
The  wort  must  be  cooled  to  a  much  lower  point  (say 
about  60°  F.),  and,  after  "  pitching,"  the  temperature 


94     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

in  the  fermenting  tun  must  be  kept  at  about  70°  to 
75°  F.  by  means  of  an  attemperator,  or  cooling  coil 
within  the  vat  (see  Fig.  28). 

Much  more  efficient  aeration  is  also  required  to  obtain 


Fig.  28. — Fermenting  Tun  with  Cooling  Coil  and  Parachute. 

a  good  crop  of  yeast  than  when  attenuation  of  the  wort 
is  the  main  object.  Various  devices  are  in  use  for  this 
purpose.  In  addition  to  the  primitive  wooden  rouser, 
a  current  of  air  is  sometimes  pumped  into  the  vat  through 


PREPARATION   OF  THE   GYLE.  95 

a  tube  which  passes  nearly  to  the  bottom  of  the  liquid, 
and  terminates  in  a  rose  or  perforated  radial  arms. 

A  common  form  of  apparatus  for  removing  the  yeast 
from  the  surface  of  the  liquid  is  that  known  as  the 
"  parachute  "  (Fig.  28).  This  consists  of  a  funnel  ending 
in  a  tube,  with  a  valve  near  the  top,  which  can  be  con- 
trolled from  the  outside.  The  yeast  is  driven  into  the 
parachute  by  means  of  a  metal  "  skimming  board/'  as 
shown,  and  is  collected  in  a  tank  below  the  tun,  where 
it  is  washed  with  water,  and  then  pumped  into  a  press. 

The  parachute  and  skimming  board  are  attached  to 
a  rack  and  pinion  work,  so  that  they  can  be  raised  or 
lowered  at  will,  and  means  are  also  provided  for  making 
the  skimming  board  sweep  over  the  surface  of  the  liquid. 

Unless  special  precautions  are  taken  to  keep  a 
low  temperature  and  to  aerate  the  liquid  thoroughly 
during  the  fermentation,  it  is  of  little  use  attempting 
to  press  the  yeast,  since  it  assumes  such  a  slimy  condition 
that  it  speedily  clogs  the  cloths  of  the  filter  press. 

The  choice  of  a  yeast  for  the  fermentation  will  largely 
depend  upon  which  of  the  two  modes  of  fermentation 
is  to  be  followed.  As  brewing  in  the  vinegar  industry 
takes  place  more  or  less  intermittently  (with  the  exception 
of  the  factories  that  manufacture  pressed  yeast),  it  is 
usually  not  practicable  to  use  the  strain  grown  in  the 
vinegar  works. 

Apart  from  that,  the  yeast  is  weakened  in  the  high 
temperature  fermentation,  and  is  less  suited  for  a  fol- 
lowing fermentation  than  a  yeast  grown  at  a  lower 
temperature. 

The  best  course  to  follow  is  to  select  the  type  of  brewers' 
or  distillers'  yeast  which  is  found  by  trial  to  be  the  most 


96    VINEGAR:  ITS  MANUFACTURE  AND  EXAMINATION. 


suitable  for  the  wort  at  the  desired  temperature,  and  to 
obtain  a  fresh  supply  thereof  for  each  brewing. 

Storage  of  the  Gyle. — After  fermentation  is  complete 


Fig.  29.— Old  Store  Vats. 

the  alcoholic  wash  is  racked  into  storage  vats,  where 
it  is  left  for  some  weeks  or  months  before  being  trans- 
ferred to  the  acetifiers.  The  longer  this  period  of  storage 


PREPARATION   OF  THE   GYLE.  97 

can  be  made  the  better  the  wash  is  suited  for  acetifica- 
tion.  Not  only  does  it  clarify  itself  spontaneously, 
throwing  down  a  deposit  of  dead  yeast  cells,  but  it  also 
undergoes  a  preliminary  acetification.  Hence  a  wash 
that  has  been  stored  for  three  months  may  contain  as 
much  as  2  per  cent,  of  acetic  acid,  and  thus  reduce  the 
time  required  for  the  work  of  the  acetifiers.  It  has  also 
the  advantage  of  keeping  the  acetifiers  cleaner  than  in 
the  case  of  freshly-fermented  gyle,  while  the  vinegar  it 
produces  can  be  obtained  in  "  bright  "  condition  much 
more  rapidly  than  is  otherwise  possible. 

For  these  reasons  it  is  the  practice  in  some  vinegar 
works  to  do  the  main  portion  of  the  brewing  at  one  time 
of  the  year,  and  to  acetify  the  wash  at  another.  It  may 
almost  be  accepted  as  an  axiom  that  the  greater  the 
storage  capacity  of  the  works  the  better  the  condition 
both  of  the  gyle  and  of  the  finished  vinegar. 


98 


CHAPTER  VII. 
ACETIFICATION  OF  THE  GYLE. 

APPABATUS  :  The  Slow  Process — Fielding — The  Orleans  Process — Claudon's 
Apparatus — The  Quick  Process — English  Acetifiers.  DISTRIBUTION 
OF  THE  GYLE  :  The  Sparger — The  Tipping  Trough — Siphon  Distri- 
butors— Aeration  Devices — Wagenmann's  Graduator — Luck's  Acetifier 
— Singer's  Apparatus — Bersch's  Acetifier.  ACETIFICATION  IN  PRACTICE  : 
Aeration — The  Temperature — Effects  of  Alcohol  and  Acetic  Acid — The 
Group  System — Disturbances  due  to  Mother-of- Vinegar — The  Vinegar 
Eel— The  Vinegar  Mite— The  Vinegar  Fly. 

The ««  Slow  "  Process. — However  the  alcoholic  wash  or  gyle 
has  been  prepared,  it  has  to  be  subjected  to  the  combined 
action  of  the  acetic  bacteria  and  atmospheric  oxygen  to 
convert  it  into  vinegar.  The  oldest  process  of  effecting 
this  change  was  by  exposing  the  casks  partially  filled 
to  the  air,  with  their  bungs  drawn  out. 

This  method,  which  is  now  obsolete  in  this  country, 
was  known  as  "  fielding,"  from  the  fact  of  the  casks 
being  exposed  in  series  of  rows  in  the  vinegar  field. 

Between  each  series  of  rows  was  an  underground  pipe 
communicating  with  a  "  back "  at  the  top  of  the  brew- 
house,  and  each  cask  was  filled  by  means  of  a  hose  attached 
to  a  cock  upon  the  distributing  pipe,  the  top  of  the  hose 
being  passed  from  cask  to  cask  as  shown  in  the  illustra- 
tion. 

During  fine  weather  the  bung-holes  were  loosely  covered 


ACETIFICATION   OF   THE   GYLE.  99 

with  pieces  of  slate,  to  prevent  access  of  dust,  but  during 
wet  weather  the  bungs  were  replaced. 

Several  months  were  required  for  the  conversion  of 
the  gyle  into  vinegar,  the  length  of  time  depending  upon 
the  temperature  of  the  atmosphere,  and  the  amount  of 
aeration  that  was  possible  by  way  of  the  bung-holes. 

When  the  fielding  was  finished  the  vinegar  was  drawn 
off  by  means  of  siphon  tubes  into  a  trough,  the  lower  end 


Fig.  30.— Vinegar  Field.     Filling  the  Casks. 

of  which  delivered  into  a  travelling  tank,  which  could 
be  moved  up  and  down  between  the  rows  (see  Fig.  31). 
Thence  it  ran  through  a  hose  and  underground  into  a 
well  in  the  building,  to  be  pumped  into  the  store  vats 
prior  to  filtration. 

This  "  slow  "  process  of  acetification  was  practically 
the  same  as  the  "  Orleans  process "  of  making  wine 
vinegar,  the  only  difference  being  that  in  the  latter  the 


100      VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 


casks  are  kept  in  a 
heated  building  and 
means  are  provided  for 
the  admission  of  more 
air. 

The  Orleans  Process. 
— The  method  of  aceti- 
fying wine  that  has 
been  used  from  time 
immemorial  in  France, 
and  especially  in  the 
district  of  Orleans, 
whence  it  takes  its 
name,  is  not  the  same 
as  that  described  by  a 
correspondent  of  the 
Royal  Society  in  1670 
(p.  5),  which  is  essen- 
tially the  modern 
"  quick  "  process. 

According  to 
Franche,*  the  reason 
why  the  Orleans  pro- 
cess has  not  been 
displaced  by  the  more 
modern  "  rapid  pro- 
cess "  is  that  it  will 
not  acetify  alcoholic 
solutions  containing  less 
than  25  per  cent,  of 

*  Manuel  Pratique  du  Fabri- 
cant  de  Vinaigre,  p.  53. 


ACETIFICATION    OF   THK    GYJLE;      ,  101 


wine.  Below  that  strength  it  is  necessary  to  add  phos- 
phates and  nitrogenous  substances  ;  and  since  these 
products  from  wine  diluted  with  alcohol  have  to  be 
sold  under  the  name  of  "  spirit  vinegar,"  the  Orleans 
process  has  come  to  be  regarded  as  the  only  possible 
method  of  making  pure  wine  vinegar. 

The  apparatus  working  by  the  "  quick  method  "  is 
stated  by  Franche  not  to  give  satisfactory  results  with 
wine  or  mixtures  of  wine  and  alcohol,  owing  to  the  tartar 
deposited  from  the  wine  clogging  the  pores  of  the  shavings 
or  other  porous  material. 

Originally  wine  vinegar  was  made  by  the  simple  method 
of  mixing  wine  with  a  little  vinegar  and  exposing  the 
mixture  to  the  air  in  open  casks.  This  primitive  method 
was  in  use  in  some  small  factories,  even  in  Orleans,  as 
late  as  1876,  although  most  vinegar  makers  had  long 
discarded  it  in  favour  of  the  "  Orleans  process/3  in  which 
the  acetification  is  effected  in  a  series  of  casks  of  special 
construction  provided  with  holes  for  the  admission  and 
outlet  of  air. 

These  casks,  which  are  termed  "  mothers,"  are  ranged 
in  tiers,  as  shown  in  the  accompanying  diagram,  usually 
in  an  underground  cellar,  the  temperature  of  which  can 
be  maintained  at  a  fairly  constant  point,  while  the  supply 
of  air  entering  through  the  door-way  can  be  regulated 
as  required.  The  cellar  is  heated  by  means  of  a  stove 
or  hot-water  pipes  to  a  temperature  which  is  never 
allowed  to  exceed  30°  C.  (86°  P.). 

Prior  to  entering  the  acetifying  casks  the  wine  is  filtered 
through  a  large  vat  containing  shavings,  which  is  known  as  a 
"  wine-rape,"  while  after  acetification  the  vinegar  is  passed 
through  a  second  rape,  and  matured  in  storage  casks. 


102    VINEGAR  :  ITS  MANUFACTURE  AND  EXAMINATION. 

The  average  quantity  of  vinegar  produced  by  each 
cask  in  a  month  is  only  about  40  litres  (8|  gallons),  and 
the  expenses  of  manufacture  range  from  about  3  to 
3J  francs  per  hectolitre. 

The  drawbacks  of  the  Orleans  process  are  that  it  is 


Fig.  32. — Manufacture  of  Wine  Vinegar,  Orleans  Process  (after 
Franche). 

very  slow,  each  cask  yielding  only  10  litres  of  vinegar 
per  week,  and  that  in  consequence  of  this  it  is  difficult 
to  eliminate  vinegar  eels  completely  from  the  casks. 
From  time  to  time  the  deposit  of  tartar  which  forms 


ACETIFICATION   OF  THE   GYLE.  103 

within  the  casks  is  removed,  but  this  does  not  take  place 
at  sufficiently  short  intervals  for  the  casks  to  be  sterilised 
and  freed  from  the  eels.  Moreover,  even  when  one  cask 
has  been  cleaned  it  speedily  becomes  infected  again  with 
eels  from  its  neighbours — a  result  which  is  much  less 
likely  to  happen  to  acetifiers  upon  a  larger  scale.  There 
is  also  a  greater  tendency  in  working  with  small  casks 
for  mother-of- vinegar  to  form,  and  to  interfere  with  the 
acetification. 

On  the  other  hand,  the  slow  working  of  the  Orleans 
process  produces  the  esters  to  which  French  vinegar 
owes  its  reputation  for  aroma  and  flavour. 

Notwithstanding  the  investigations  of  Pasteur,  which 
showed  in  what  directions  the  Orleans  process  could 
be  improved,  there  has  been  but  little  progress  in  the 
manufacture.  The  apparatus  devised  by  Pasteur  con- 
sisted of  large  shallow  troughs  with  holes  at  the  side 
for  the  admission  of  air.  The  amounts  of  vinegar  with- 
drawn and  of  fresh  wine  added  were  regulated  in  accord- 
ance with  the  speed  of  acetification,  so  that  the  bacteria 
always  had  a  sufficient  supply  of  alcohol,  and  therefore 
did  not  attack  the  acetic  acid.  The  wine  was  sterilised 
before  acetification  to  destroy  foreign  organisms,  while 
the  finished  vinegar  was  treated  in  the  same  way  to  ensure 
its  keeping. 

Claudon's  Apparatus. — This  plant  was  devised  by 
Claudon  to  embody  the  principles  of  Pasteur's  teaching 
while  being  practicable  upon  a  manufacturing  scale. 

It  consisted  essentially  of  a  series  of  superposed  shallow 
fermentation  vessels  C,  C,  C,  in  a  square  tank,  about 
6  feet  high,  which  was  carried  on  stone  pillars  B. 

The  bottom  of  each  fermentation  vessel  formed  the 


104      VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

cover  of  the  next  one,  while  a  floating  box  of  special 
form  was  placed  in  each  to  keep  the  bacteria  (My  coder  ma) 
at  the  surface  of  the  liquid. 

In  each  fermentation  vessel  were  ten  openings  E,  five 
on  each  side,  the  admission  of  air  through  each  being 
controlled  by  a  movable  glass  panel. 

The  wine  was  heated  to  a  maximum  temperature  of 
55°  C.  in  the  vat  H,  whence  it  passed  into  the  acetifying 


Fig.  33. — ClaUdon's  Acetifying  Apparatus  (after  Franche). 

vessel,  while  the  vinegar  was  drawn  off  into  the  vat  L, 
and  filtered  through  wire  gauze  filters  with  wool,  which 
were  contained  in  the  vat  N.  Each  tank  A  worked  for 
about  ten  days  before  being  cleaned  and  recharged. 

As  in  the  original  Orleans  process,  the  alcoholic  liquid 
(gyle)  remained  quiet,  while  its  surface  was  exposed  to 
the  action  of  the  air,  and  the  advantage  of  this  apparatus 


ACETIFICATION   OF   THE   GYLE.  105 

was  that  the  shallow  form  of  the  fermentation  vessels 
allowed  much  more  exposure  of  liquid  than  was  possible 
in  ordinary  casks. 

The  "Quick"  Process. — The  general  introduction  of 
the  so-called  "  quick  "  process  of  acetification  is  attri- 
buted to  Schiitzenbach,  who  introduced  it  into  Germany 
in  1823.  In  all  main  essentials,  however,  the  quick 
process  is  only  a  development  of  the  method  of  aceti- 
fication used  in  certain  wine-vinegar  factories  in  France 
in  1670  (see  p.  5). 

The  main  difference  introduced  by  Schiitzenbach  was 
the  use  of  a  vat  instead  of  a  cask  as  an  acetifier,  with 
mechanical  means  for  the  repeated  distribution  of  the 
gyle  over  the  acetifying  medium. 

Until  about  sixty  years  ago  both  processes  of  acetification 
were  in  use  in  English  vinegar  works,  part  of  the  vinegar 
being  prepared  by  fielding,  and  the  remainder  by  stoving, 
as  it  was  called. 

English  Acetifiers. — The  main  differences  between 
English  and  German  acetifiers  are  that  the  former  are 
made  upon  a  larger  scale  than  the  latter,  and  as  they 
are  used  for  acetifying  an  extract  of  grain  rather  than 
an  alcoholic  wash,  must  be  provided  with  a  larger  supply 
of  air. 

The  acetifiers  introduced  into  British  vinegar  works, 
at  the  time  when  the  "stoves"  replaced  the  vinegar 
fields,  consisted  of  large  vats  taking  a  charge  of  2,000  to 
3,000  gallons. 

About  two-thirds  of  the  way  up  a  perforated  false 
bottom  was  fixed,  and  the  space  above  this  was  loosely 
packed  with  raisin  stalks  or  shavings  of  beech  wood, 
upon  which  the  bacteria  developed,  while  a  current  of 


106     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

air  was  admitted  through  a  number  of  holes  bored  in  the 
side  of  the  vat  below  the  false  bottom. 

The  gyle  was  distributed  in  a  fine  rain  over  the  shavings 
by  a  revolving  sparge,  and  running  downwards  encoun- 
tered the  currents  of  air,  which  enabled  the  bacteria  to 
acetify  a  small  amount  of  the  alcohol. 

The  liquid  collecting  in  the  bottom  of  the  vat  was 
pumped  up  again  into  the  sparge  box,  whence  it  was 
once  more  distributed  over  the  shavings,  and  this  process 
was  continually  repeated  for  two  to  three  weeks,  until 
nearly  the  whole  of  the  alcohol  had  been  converted  into 
acetic  acid. 

When  freshly  started  these  acetifiers  worked  very 
well,  but  the  shavings  soon  became  clogged  by  mother- 
of-vinegar,  and  where  this  happened  the  air  was  no 
longer  evenly  distributed  throughout  the  acetifying 
medium,  but  made  channels  for  itself.  Hence  some 
parts  received  an  excessive  supply  of  oxygen,  whereas 
in  other  places  there  was  a  deficiency,  and  the  practical 
result  was  that  part  of  the  alcohol  was  not  oxidised 
beyond  the  stage  of  aldehyde,  while  another  part  was 
oxidised  beyond  the  stage  of  acetic  acid,  and  was  lost. 

For  these  reasons  shavings  were  replaced  in  many 
vinegar  works  by  wicker  basket  work.  This  was  much 
less  liable  to  become  clogged  than  the  shavings,  and  allowed 
the  air  to  circulate  more  regularly. 

A  section  of  part  of  an  acetifier  constructed  on  these 
lines  is  shown  in  Fig.  34. 

Distribution  of  the  Gyle. — One  of  the  most  important 
factors  in  acetification  is  the  distribution  of  the  wash 
over  the  acetifying  medium  in  the  finest  possible  state 
of  division. 


ACETIFICATION    OF   THE    GYLE.  107 

The  most  general  method  of  effecting  this  division  is 
by  the  use  of  the  sparge.  This  is  frequently  constructed 
upon  the  same  principle  as  the  sparge  used  in  the  mash- 
tun  (p.  80),  but  it  is  made  of  vulcanite  or  block  tin,  to 
resist  the  action  of  the  hot  acetic  acid. 

In  the  largest  acetifiers  the  sparge  is  often  made  of 
wood,  and  is  in  the  form  of  a  tapering  box  pierced  by 
holes  at  the  sides  and  with  an  open  top  to  facilitate 
cleaning  at  intervals. 


G,  Supply  pipe  from  pump.  R,  R,  The  sparge. 

S,  Perforated  support. 

Fig.  34. — Section  of  a  Modern  Acetifier  with  Basket  Work. 

Such  heavy  sparges  will  not  revolve  by  the  force  of 
the  escaping  liquid,  and  require  to  be  driven  by  a  cog- 
wheel, whereas  in  the  case  of  the  light  vulcanite  sparges 
the  revolution  is  produced  by  the  force  of  liquid.  This 
has  the  advantage  that  any  failure  in  the  action  is  at  once 
shown  by  the  stoppage  of  an  outside  indicator  attached 


108      VINEGAR  :    ITS   MANUFACTURE   AND   EXAMINATION. 

to  the  sparge.  On  the  other  hand,  the  narrow  tubular 
sparges  are  much  more  liable  to  become  clogged  with 
mother-of-vinegar  than  the  large  wooden  box  sparges, 
from  which  any  accumulation  of  "  mother "  is  often 
expelled  by  the  force  of  the  liquid. 


Fig.  35. — Sparge  of  an  Acetifier  (Bronner). 

The  Tipping  Trough. — An  ingenious  device  for  dis- 
tributing the  wash  over  the  surface  of  the  acetifying 
medium  is  shown  in  Fig.  36.  It  consists  of  a  wide-angled 
trough  with  a  partition  in  the  middle,  so  as  to  form  the 
two  compartments  a  and  b.  At  the  angle  c  there  is  an 


ACETIFICATION   OF  THE   GYLE.  109 

axis  upon  which  the  trough  can  swing  either  to  the  right 
or  to  the  left  as  far  as  the  stops  d.  The  wash  pumped 
from  the  bottom  of  the  acetifier  falls  through  the  tap 
into  one  of  the  compartments  until  this  is  filled  to  a  certain 
height.  It  then  tips  over  and  discharges  the  wash  over 
the  surface  of  the  acetifying  medium,  while  the  empty 
compartment  is  at  the  same  time  brought  beneath  the 
tap  to  be  filled  and  discharged  in  the  same  way.  This 
process  continues  alternately,  so  that  each  side  of  the 
surface  of  acetifying  medium  is  alternately  flushed  with 
a  large  volume  of  the  liquid. 

With  small  acetifiers  this  device  works  admirably, 
but  it  is  unsuitable  for  acetifiers  of  even  moderately 
large  dimensions,  as  the  weight 
of  liquid  in  the  compartment  is 
so  great  that  in  its  sudden  fall  it 
produces  a  great  strain  on  the 
apparatus. 

Siphon    Distributors.  —  Another 
method  of  distributing  the  wash      Y^  36.-TiPPing  Trough 

....  ,         1,1  (Bronner). 

is  to  pump  it  into  a  closed  tank 

above  the  acetifier.  In  this  tank  is  a  siphon  tube,  the 
longer  limb  of  which  discharges  the  liquid  into  a  tray 
pierced  with  numerous  small  holes  within  the  acetifier, 
whence  it  trickles  in  fine  streams  over  the  shavings 
or  basket  work. 

The  air  required  in  the  siphon  tank  is  drawn  from  the 
space  at  the  top  of  the  acetifier,  so  that  the  aeration  of 
the  wash  remains  under  control. 

In  some  apparatus  a  combination  of  the  siphon  tube 
and  sparge  is  employed  with  the  object  of  automatically 
regulating  the  supply  of  wash  to  the  acetifier.  This 


110    VINEGAR:  ITS  MANUFACTURE  AND  EXAMINATION. 

arrangement  is  shown  in  Fig.  37.  The  liquid  pumped 
from  the  base  of  the  acetifier  is  delivered  into  the  small 
cask  c,  through  the  pipe  ?>.  When  it  reaches  a  certain 
level  it  is  drawn  over  through  the  glass  siphon  d  into 
the  funnel  e  of  the  sparge  /,  and  is  thence  distributed 
by  the  revolving  arms  g,  g.  The  point  on  which  the 
sparge  revolves  is  shown  at  h,  while  i  represents  the 
cover  of  the  acetifier,  and  k,  k  holes  for  the  escape  of 
the  air.  The  flow  of  the  wash  into  the  acetifier  can 


Fig.  37. — Combined  Siphon  and  Sparge. 

thus  be  readily  controlled  by  regulating  the  opening 
of  the  cock  at  6,  and  by  raising  or  lowering  the  siphon 
tube. 

Aeration  Devices. — The  most  simple  method  of  supply- 
ing air  to  the  acetifiers  is  by  piercing  a  number  of  small 
holes  in  the  sides  of  the  vat  below  the  false  bottom  that 
supports  the  acetifying  medium. 

An  effective  arrangement  is  to  have  from  6  to  12  holes 
with  a  diameter  of  about  f  inch,  and  it  is  preferable  to 


ACETIFICATIO2ST   OF  THE   GYLE. 


Ill 


have  glass  tubes  projecting  from  some  of  these  into  the 
interior  of  the  vat. 

The  object  of  this  will  be  seen  by  reference  to  the 
accompanying  diagram  (Fig.  38),  which  represents  a  ver- 
tical section  of  an  acetifier.  The  air  entering  through  the 
holes  at  the  bottom  must  tend  to  rise  vertically  upwards 
until  it  escapes  through  the  openings  b  near  the  centre 
of  the  cover.  There  will  thus  be  a  large  cone-shaped 
area  A,  where  the  aeration  will  be  less  complete  than 


Fig.  38. — Diagram  showing  Aeration  of  an  Acetifier. 

at  the  outside  B,  B.  This  less  active  space  becomes 
larger  with  the  increase  in  the  diameter  of  the  vat,  so 
that  for  this  reason  the  aeration  in  small  acetifiers  is 
frequently  more  uniform  than  in  larger  apparatus. 

By  passing  tubes  a  foot  or  more  into  the  interior  through 
alternate  holes,  the  aeration  will  tend  to  become  more 
regular  throughout  the  whole  of  the  acetifying  medium. 

Another  way  of  aerating  the  interior  is  by  means  of 
an  air  tube  in  the  bottom  of  the  acetifier.  This  projects 


112     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

upwards  nearly  to  the  level  of  the  false  bottom,  and  is 
protected  from  the  falling  vinegar  by  a  conical  roof 
supported  on  a  tripod  (Fig.  39).  The  air  escaping  from 


Fig.  39. — Aeration  Device. 


Fig.  40.— Aeration  Tubes. 

the  central  tube  is  distributed  by  contact  with  this  roof, 
and  rises  through  the  middle  of  the  acetifier. 


ACETIFICATION    OF   THE   GYLE. 


113 


The  same  end  is  effected  by  an  aeration  tube  of  the 
form  shown  in  Fig.  40,  in  which  holes  for  the  escape 
of  the  air  are  provided  beneath  the  conical  cover. 

The  outlets  for  the  escape  of  the  air  should  be  of  larger 
size  than  the  inlets,  and  are  preferably  to  be  placed  near 
the  middle  of  the  cover.  Sliding  shutters,  which  can  be 
drawn  across  the  top  openings,  enable  the  air  supply  to 
be  regulated  in  accordance  with  the  yields  of  acetic 
acid  obtained  from  the  alcohol  in  the  wash. 

Each  acetifier  will  vary  in  its 
speed  of  action  and  its  uniformity 
of  acetification,  and  it  is,  therefore, 
necessary  to  vary  the  conditions  of 
aeration  in  every  instance  until 
satisfactory  results  have  been 
obtained. 

The  diameter  of  the  outlet 
openings  at  the  top  ought  to  equal 
the  sum  of  the  diameter  of  the 
inlets  at  the  sides. 

Wagenmann's  Graduator. — A  form  of  acetifier  working 
by  the  "  quick  process  "  was  devised  about  1830  by  M. 
Wagenmann.  This  consisted  of  a  small  oak  cask  about 
5J  feet  high  by  3J  feet  in  diameter  at  the  top.  A  -series 
of  holes  was  pierced  at  about  15  inches  from  the  bottom, 
for  the  admission  of  air,  while  the  liquid  to  be  acetified 
was  poured  in  through  a  funnel  at  the  top.  At  about 
5  inches  from  the  lid  of  the  cask  a  perforated  shelf  was 
fixed,  and  through  each  of  the  400  holes  cotton  or  hemp 
wick  was  suspended  to  guide  the  liquid  downwards  on 
to  the  beech  shavings,  with  which  the  acetifier  was 

packed.     There  were  also  four  larger  holes  in  this  shelf, 

8 


Fig.  41. — Wagenmann's 
Graduator. 


114    VINEGAR:  ITS  MANUFACTURE  AND  EXAMINATION. 

in  which  were  fixed  short  glass  tubes  projecting  above 
and  below  the  wood.  These  were  intended  for  the  escape 
of  the  air  admitted  through  the  holes  below.  After 
acetification  was  complete  the  vinegar  was  drawn  off 
through  the  siphon  tube  at  the  base. 

In  this  gmduator,  with  its  suspended  cords,  we  have 
the  germ  of  the  idea  utilised  in  Luck's  acetifier,  in  which 
the  acetifying  medium  consists  of  bunches  of  cords 
stretched  between  the  distributing  tray  and  the  false 
bottom. 

Singer's  Apparatus. — This  is  composed  of  a  series  of 
rectangular  boxes,  which  are  superposed  above  each 
other.  In  each  of  these  is  a  series  of  wooden  tubes  packed 
with  shavings  or  charcoal,  and  the  wash  is  made  to  trickle 
through  these  successively  from  top  to  bottom,  while 
air  is  admitted  through  ventilators  at  the  sides  and  at 
the  top. 

To  prevent  loss  of  heat,  the  entire  apparatus  is  enclosed 
in  a  case  with  glass  windows. 

It  is  obvious  that  the  acetification  surface  is  much 
too  small  for  effective  working,  and  that  this  apparatus, 
which  is  described  in  most  of  the  foreign  text-books, 
would  be  quite  unsuitable  for  the  manufacture  of  vinegar 
on  a  large  scale. 

Bersch's  Acetifier. — An  Austrian  apparatus,  which  is 
claimed  to  give  excellent  results  in  practice,  is  shown  in 
the  accompanying  figure  (Fig.  43).  The  wash  is  siphoned 
over  from  the  trough  at  the  top,  and  slowly  percolates 
through  layers  of  superposed  flat  plates  with  narrow 
spaces  between  them. 

Although  this  acetifier  is  suitable  for  the  acetification 
of  small  quantities  of  an  alcoholic  wash,  such  as  is  used 


ACETIFICATION   OF   THE   GYLE. 


115 


in  Germany  and  Austria,  it  could  not  be  effectively 
used  with  a  malt  wash,  since  the  spaces  between  the 
plates  would  become  rapidly  clogged  with  mother-of- 
vinegar. 

Theoretically  it  offers  a  large  superficial  area  for  the 
growth  of  the  bacteria,  but  the  frequent  cleaning  that 


Fig.  42.— Singer's  Acetifier. 


Fig.  43. — Bersch's  Acetifier. 


it  would  require   under  English  conditions   of  working 
would  render  its  use  unprofitable  in  this  country. 

ACETIFICATION  IN  PRACTICE. 

Whatever  form  of  acetifier  be  employed,  the  conditions 
for  economical  working  are  essentially  the  same,  and  the 


116    VINEGAR:  ITS  MANUFACTURE  AND  EXAMINATION. 

superiority  of  one  type  of  apparatus  over  another  depends 
upon  the  extent  to  which  these  conditions  are  satisfied. 

Aeration. — If  it  were  possible  always  to  supply  the 
acetic  bacteria  throughout  the  whole  of  the  acetifier 
with  exactly  the  right  amount  of  air,. the  conversion  of 
alcohol  into  acetic  acid  would  under  the  normal  con- 
ditions of  working  be  theoretical ;  but,  as  a  rule,  in 
practice,  the  aeration  process  is  far  from  perfect,  and 
considerable  losses  of  alcohol  and  acetic  acid  take  place 
owing  to  the  admission  of  either  too  much  or  too  little 
air. 

For  example,  in  the  old  type  of  acetifiers,  packed  with 
beech  shavings,  the  admission  of  air  is  by  no  means 
uniform  throughout  the  material.  In  some  places,  where 
the  mother-of- vinegar  has  fallen  upon  the  shavings,  the 
air  passages  become  blocked  and  the  acetification  is 
incomplete,  while  in  other  places  the  air  will  pass  more 
freely,  and  if  present  in  too  large  proportion  will  lead  to 
the  oxidation  of  the  acetic  acid  already  formed.  Hence 
all  stages  of  oxidation  will  be  taking  place  simultaneously 
in  the  acetifier,  and  the  total  result  will  be  a  reduced 
yield  of  acetic  acid,  the  deficiency  usually  ranging  from 
about  10  to  25  or  30  per  cent.,  but  sometimes  reaching 
40  per  cent,  or  more. 

The  substitution  of  basket  work  for  shavings,  as  is 
found  in  many  of  the  English  acetifiers,  is  a  distinct 
improvement,  since  it  causes  the  aeration  to  be  more 
regular,  and  reduces  the  tendency  to  the  formation  of 
air  channels,  but  this  type  of  apparatus  soon  becomes 
clogged,  and  requires  frequent  cleansing  if  it  is  to  work 
effectively. 

In     some    of    the     Continental    types    of    acetifiers. 


ACETIFICATION   OF  THE   GYLE.  117 

in  which  the  gyle  is  made  to  trickle  through  tubes, 
regular  aeration  is  more  possible,  although  some  of 
these  apparatus  are  hardly  suitable  for  working  under 
conditions  in  which  the  bacteria  produce  an  excessive 
quantity  of  "  mother/' 

The  whole  problem  of  successful  acetification  depends 
upon  presenting  the  largest  possible  surface  for  the 
development  and  aeration  of  the  bacteria  in  a  uniform 
manner,  and  of  preventing  the  air  passages  from  becoming 
clogged  through  the  development  of  the  zoogloeal  con- 
dition of  the  micro-organisms.  The  solution  of  the 
difficulty  is  not  as  simple  as  at  first  sight  might  appear, 
although  some  types  of  apparatus  which  the  writer  has 
had  the  opportunity  of  examining  under  working  con- 
ditions undoubtedly  give  results  very  much  nearer  to 
theoretical  requirements  than  do  the  average  acetifiers 
used  in  this  country. 

An  important  factor  which  must  be  taken  into  con- 
sideration is  the  relationship  between  the  economy  of 
acetification  and  the  speed  with  which  the  acetifying 
medium  becomes  clogged.  The  better  the  results  obtained 
in  the  acetification  the  sooner  will  the  vat  require  cleaning, 
owing  to  the  porous  medium  becoming  clogged.  For 
example,  a  packing  of  fine  wicker-work  will  give  good 
results  at  first,  but  after  a  month  or  so  it  gradually  be- 
comes clogged  and  begins  to  work  irregularly,  and  with  a 
greater  loss  of  acetic  acid.  It  will  then  require  cleaning 
and  starting  again,  which  in  itself  involves  a  loss  of  the 
acetic  acid  with  which  the  basket  work  has  become 
impregnated. 

The  same  difficulty  attaches  'to  some  of  the  "  plate " 
acetifiers,  in  which  the  wash  is  acetified  between 


118    VINEGAR:  ITS  MANUFACTURE  AND  EXAMINATION. 

narrow  parallel  surfaces.  At  first,  these  work  very  well, 
and  allow  the  air  to  be  evenly  regulated  through  all 
parts  of  the  acetifier,  but  under  English  conditions,  at 
all  events,  they  soon  become  coated  with  a  slimy  deposit, 
and  must  be  cleaned  again. 

Hence  it  is  necessary  to  regulate  the  aerating  surfaces 
in  an  acetifier  in  such  a  way  that  the  loss  of  alcohol 
involved  in  working  with  a  more  open  medium  (e.g., 
basket  work  of  wider  mesh)  is  more  than  counterbalanced 
by  the  saving  in  labour  effected  by  the  less  frequent 
cleaning  of  the  acetifiers,  which  is  then  required. 

The  Temperature. — After  regulation  of  the  supply  of 
air,  the  most  important  factor  for  the  successful  working 
of  an  acetifier  is  that  the  temperature  should  be  kept 
within  definite  limits. 

It  has  already  been  shown  (p.  42)  that  the  optimum 
temperature  for  the  acetification  of  alcohol  varies  with 
different  species  of  bacteria,  although  in  practice  it  is 
quite  possible  to  acclimatise  the  micro-organisms  to 
abnormal  temperatures. 

On  the  Continent  the  species  of  acetic  bacteria  in 
common  use  work  best  at  a  much  lower  temperature 
than  is  usual  in  this  country.  Thus  in  some  of  the  small 
German  acetifiers  the  temperature  is  kept  at  about 
90°  to  95°  F.,  and  acetification  wrould  cease  if  the  tem- 
perature rose  much  above  100°  F.  In  England,  however, 
the  acetifiers  work  best  at  temperatures  of  about  105° 
to  110°  F.,  and  the  temperature  can  be  brought  still 
higher  without  injuring  the  bacteria. 

If  small  acetifiers  providing  a  relatively  large  surface 
for  aeration  be  employed,  the  temperature  will  rise 
spontaneously  to  the  optimum  point,  but  with  larger 


ACETIFICATION   OF  THE   GYLE.  119 

quantities  of  gyle,  or  with  acetifiers  in  which  the  aeration 
surface  is  relatively  smaller,  it  is  advisable  to  heat  the 
liquid  to  about  70°  F.  before  starting  the  acetification 
process. 

In  the  case  of  the  largest  acetifiers,  taking  a  charge 
of  4,000  to  5,000  gallons,  it  is  usual  to  heat  the  liquid 
in  the  acetifier  itself  by  means  of  a  steam  coil  at  the 
bottom  of  the  vat.  For  smaller  acetifiers  the  preliminary 
heating  is  conveniently  done  in  a  tank  (lined  with  block 
tin),  fixed  at  a  level  above  a  series  of  acetifiers,  into  any 
of  which  it  can  be  discharged  when  sufficiently  heated. 

In  the  Continental  factories  the  whole  of  the  acetifying 
room  is  usually  heated  by  means  of  a  stove,  and  this 
course  has  the  advantage  that  currents  of  cold  air  are 
prevented  from  entering  the  acetifiers  and  causing  ir- 
regular acetification. 

After  the  initial  heating  of  the  gyle  in  English  acetifiers 
the  bacterial  oxidation  raises  the  temperature  to  a  point 
which  will  depend  to  a  large  extent  upon  the  amount  of 
air  supplied,  so  that  the  daily  readings  of  the  thermometers 
inserted  into  a  hole  in  the  side  of  the  acetifier  afford  an 
index  of  the  regularity  of  the  acetification. 

If  too  much  air  is  being  supplied,  the  temperature  will 
rush  up  very  rapidly,  and  it  will  then  be  found  that,  not 
only  is  the  alcohol  being  rapidly  acetified,  but  that  the 
acetic  acid  produced  is  also  being  oxidised. 

On  the  other  hand,  if  the  temperature  rises  very  slowly, 
or  even  falls,  insufficient  air  to  promote  the  oxidation  is 
being  supplied,  and  the  openings  must  be  regulated 
accordingly. 

One  advantage  possessed  by  the  English  in  comparison 
with  the  Continental  process  is  that  the  higher  temperature 


120      VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

checks  the  development  of  vinegar  eels  and  their  effects 
upon  the  oxidation  (p.  124). 

It  is  very  rarely  that  these  organisms  will  develop  in 
an  acetifier  in  which  the  temperature  exceeds  100°  F., 
although  it  is  interesting  to  note  that,  like  the  acetic 
bacteria,  the  vinegar  eel  can  become  gradually  acclima- 
tised to  higher  temperatures.  In  the  case  of  acetifiers 
working  at  about  90°  F.,  it  is  difficult  to  prevent  their 
appearance,  unless  special  precautions  be  taken  to  use 
a  sterilised  wash,  and  to  protect  the  air-holes  of  the 
acetifier. 

On  the  other  hand,  the  high  temperatures  that  are 
required  for  rapid  acetification  cause  loss  of  volatile 
products,  especially  aldehyde,  through  evaporation.  To 
obviate  this  it  is  essential  to  prevent,  as  far  as  possible, 
the  escape  of  air  from  the  acetifying  chambers,  or 
"  stoves,"  as  they  are  termed  by  the  workmen. 

Any  outlet  for  the  hot  air  at  the  top  of  the. building 
increases  this  loss,  by  allowing  the  volatile  products  to 
escape,  instead  of  being  gradually  drawn  back  again  into 
the  acetifiers  and  further  oxidised. 

The  Group  System. — The  strength  of  vinegar  that  can 
be  obtained  directly  from  the  acetifiers  is  restricted  by 
the  fact  that  the  bacteria  are  sensitive  to  the  action 
both  of  strong  alcohol  and  of  acetic  acid.  Alcohol  in  the 
proportion  of  about  10  per  cent,  kills  them,  but  long 
before  that  strength  is  reached  their  activity  is  checked. 
On  the  other  hand,  they  offer  much  greater  resistance 
to  acetic  acid,  and  do  not  reach  their  full  vital  activity 
until  the  acidity  reaches  about  2  per  cent. 

On  these  facts  is  based  the  group  system  of  acetification, 
which  consists,  in  brief,  of  acclimatising  the  bacteria  to 


ACETIFICATION   OF  THE   GYLE.  121 

thrive   best   under   certain   conditions   of   alcoholic   and 
acetic  strength. 

It  is  not  possible  to  produce  a  12  per  cent,  vinegar 
directly  from  one  acetifier,  since  the  proportion  of  alcohol 
required  would  be  fatal  to  the  bacteria.  Hence,  in  the 
production  of  concentrated  vinegars,  such  as  Essigsprit, 
the  acetification  is  carried  out  in  three  groups  of  acetifiers. 
The  first  of  these  is  charged  with  a  wash  capable  of 
yielding  about  6  per  cent,  of  acetic  acid.  The  vinegar 
leaving  these  is  fortified  with  an  alcoholic  wash  (usually 
potato  or  grain  spirit),  in  sufficient  quantity  to  yield  a 
vinegar  of  9  to  10  per  cent,  strength  in  the  second  group 
of  acetifiers,  while  in  like  manner  the  vinegar  from  these 
is  again  fortified  before  being  transferred  to  the  third 
group  of  acetifiers,  where  the  acetification  is  completed. 

Such  a  method  of  working  is  only  possible  where  a 
strong  alcoholic  wash  is  obtainable. 

Disturbances  due  to  Mother-of-Vinegar. — However  care- 
fully the  supply  of  air  to  the  acetifiers  and  the  tempera- 
ture are  controlled,  it  is  impossible  to  prevent  a  gradual 
accumulation  of  mother-of- vinegar  upon  the  baskets  or 
porous  packing  in  the  vat.  When  once  this  "  tripe," 
as  the  workmen  term  it,  begins  to  form,  the  proper  supply 
of  air  is  checked,  and  under  these  conditions  the  growth 
of  the  mother-of -vinegar  increase  still  further. 
-.  The  formation  of  this  remarkable  zooglceal  condition 
of  the  bacteria  (see  p.  34)  appears  to  be  promoted  by 
the  presence  of  a  limited  supply  of  air. 

For  example,  if  a  bottle  of  freshly-made  vinegar  be 
tightly  corked  no  alteration  beyond  a  slight  deposition 
of  albuminous  matter  will  take  place,  but  if  the  cork 
be  slightly  loosened  so  that  a  trace  of  air  gains  admission 


122     VINEGAR  :    ITS   MANUFACTURE    AND   EXAMINATION. 

to  the  liquid,  a  succession  of  solid  gelatinous  wads  will 
form  in  the  neck,  and  eventually  fall  to  the  bottom. 
This  is  commonly  described  as  the  vinegar  "  becoming 
mothery,"  and  is  the  cause  of  occasional  complaints. 
It  is  completely  cured  by  sterilisation  (see  p.  132). 

The  Vinegar  Eel. — As  is  mentioned  above,  one  of  the 
greatest  troubles  with  which  the  vinegar  maker  has  to 
contend  is  the  minute  animal  known  as  the  vinegar  eel. 

There  are  numerous  references  to  it  in  scientific  litera- 
ture, one  of  the  earliest  being  in  the  Philosophical  Essays 
of  Robert  Boyle  (1661)  : — "We  have  made  mention  to 
you  of  a  great  store  of  living  creatures  which  we  have 
observed  in  vinegar  ;  of  the  truth  of  which  observation 
we  can  produce  divers  and  severe  witnesses,  who  were 
not  to  be  convinced  until  we  had  satisfied  them  by  ocular 
demonstration ;  and  yet  there  are  divers  parcels  of 
excellent  vinegar  wherein  you  may  in  vain  seek  for  these 
living  creatures,  and  we  are  now  distilling  some  of  that 
liquor,  wherein  we  can  neither  by  candle  light  nor  by 
daylight  discern  any  of  these  little  creatures,  of  which 
we  have  often  seen  swarms  in  other  vinegars." 

The  occurrence  of  eels  in  vinegar  did  not  escape  the 
notice  of  Leeuwenhoeck,  who  has  the  following  amusing 
reference  to  them  *  :—  ''  I  have  also  described  a  full- 
grown  live  eel,  such  a  one  whereof  there  were  many  more 
in  the  vinegar.  I  cannot  but  take  notice  how  some  men 
are  deceived  that  think  of  the  sourness  of  vinegar  proceeds 
from  eels  pricking  their  tongues  with  their  tails,  for  if 
this  were  true,  then  would  some  vinegar  be  flat  because 
there  are  no  eels  in  it,  or  rather  eels  are  dead  in  it,  as  is 
usual  in  cold  or  frosty  weather/' 

*  Trans.  Roy.  Soc.,  1685,  xv.,  965. 


ACETIFICATION   OF  THE   GYLE.  123 

The  organism  to  which  these  statements  refer  is  the 
Leptodera  oxophila,  and  appears  to  be  identical  with  the 
"  eels  "  that  will  develop  in  sour  paste. 

It  is  of  very  frequent  occurrence  in  Continental  vinegar 
works,  where  the  vinegar  is  manufactured  at  a  lower 
temperature  than  is  usual  in  England.  According  to 
Czernat,  it  may  be  introduced  into  the  vinegar  from  the 


Fig.  44.— Vinegar  Eels  (Pasteur). 

water,  but  it  is  much  more  probable  that  it  is  derived 
from  the  air. 

Occasionally  when  vinegar  is  exposed  to  the  air  for 
a  short  time  it  will  swarm  with  these  creatures,  and  the 
same  thing  may  happen  in  an  acetifier,  so  that  every 
drop  of  the  vinegar  has  the  appearance  shown  in  Fig.  44. 


124     VINEGAR  t    ITS   MANUFACTURE   AND    EXAMINATION. 

The  structure  of  the  vinegar  eel  is  very  simple  (Fig.  45), 
the  body  is  cylindrical,  and  ends  in  a  sharp  point,  and 
the  skin,  which  is  changed  from  time  to  time,  is  smooth, 
structureless,  and  very  strong.  According  to  Czernat's 
average  measurements,  the  length  of  the  male's  body  is 
about  ^g.  inch,  and  that  of  the  female  about  ^  inch. 

Vinegar  eels  move  either  backwards  or  forwards,  and 
progress  by  alternately  shaping  themselves  into  an  S 
and  straightening  out  again.  They  appear  to  be  in- 
cessantly darting  through  the  vinegar  in  all  directions, 
but  always  with  a  tendency  towards  the  surface,  for 
they  are  air-breathing  animals. 


Fig.  45. — Vinegar  Eel,  highly  magnified  (Pasteur). 

They  are  capable  of  living  in  very  dilute  alcohol  or 
acetic  acid,  as  well  as  in  vinegar,  and  can  resist  great 
variations  in  temperature,  not  being  killed  until  the 
temperature  reaches  140°  to  150°  F.  in  one  direction  or 
22°  F.  in  the  other. 

Pasteur*  was  the  first  to  point  out  how  harmful  the 
vinegar  eel  was  in  the  manufacture  of  vinegar.  Should 
they  develop  within  an  acetifier  a  struggle  for  air  begins 

*  Loc.  cit. 


ACETIFICATION    OF   THE   GYLE.  125 

between  them  and  the  acetic  bacteria.  For  a  time  a 
working  balance  may  be  struck  between  them,  and  the 
air  shared  ;  but  during  this  struggle,  which  may  last  for 
weeks,  the  activity  of  the  bacteria  is  impaired,  and  though 
the  conversion  of  alcohol  into  acetic  acid  still  proceeds, 
it  does  so  with  an  increased  expenditure  of  time  and  a 
reduced  yield. 

Should  the  vinegar  eels  gradually  obtain  the  upper 
hand,  they  interfere  more  and  more  with  the  working 
of  the  apparatus,  and  eventually  the  acetification  comes 
to  a  standstill.  If,  on  the  other  hand,  the  bacteria  get 
the  mastery,  they  tend  to  deposit  "  mother "  on  the 
surface  of  the  liquid,  as  the  result  of  their  obtaining 
insufficient  oxygen.  This  skin  effectually  prevents  the 
eels  from  breathing  when  they  come  to  the  surface,  and 
so  they  perish  and  fall  to  the  bottom  of  the  acetifier, 
where  they  accumulate  as  a  white  deposit  and  may 
putrefy.  In  either  case  the  only  remedy  is  to  clean  and 
disinfect  the  apparatus  and  start  afresh. 

It  was  only  with  difficulty  that  Pasteur  could  convince 
certain  French  vinegar  makers  of  the  advantage  of  getting 
rid  of  the  vinegar  eel,  for  so  general  had  it  become  with 
them  that  they  had  begun  to  look  upon  it  as  an  essential 
part  of  the  process  instead  of  a  deadly  enemy. 

Even  after  vinegar  containing  eels  has  been  freed  from 
them  by  nitration  the  ova  remain,  and  under  suitable 
condition  will  develop  into  eels,  which  will  rapidly  multiply 
and  make  the  vinegar  appear  turbid,  though  without 
materially  affecting  its  acetic  strength.  This  after- 
development  of  eels  is  easily  prevented  by  heating  the 
vinegar  to  160°  F.  in  a  sterilising  apparatus,  as  described 
on  p.  133. 


126     VINEGAR  :    ITS    MANUFACTURE   AND    EXAMINATION. 

The  Vinegar  Mite. — Another  enemy  of  the  acetic 
bacteria  is  known  as  the  "  vinegar  mite."  When  once 
it  obtains  a  footing  within  an  acetifier  it  multiplies 
rapidly,  interferes  with  the  oxidation,  and  is  not  easily 
exterminated.  Bersch  records  a  case  that  came  under 
his  observation.  The  vinegar  made  in  a  certain  Italian 
factory  swarmed  with  these  mites,  which  had  finally 
brought  the  acetification  to  a  complete  standstill.  The 
manufacturers  attributed  their  presence  to  the  soil  below 
the  acetifiers,  but  had  no  idea  that  they  pointed  to  a 
want  of  care. 

It  is  through  the  aeration  holes  in  the  acetifiers  that 
the  mites  gain  access  to  the  apparatus,  and  attempts 
have  been  made  to  prevent  this  by  placing  bird-lime 
round  the  outside  of  the  holes,  while  in  some  of  the 
more  recent  patents  fine  wire  gauze  is  used  for  the  same 
purpose. 

At  first  the  acetic  bacteria  do  not  appear  to  be  much 
affected  by  the  presence  of  the  mites,  but  as  these  increase 
.and  then  die  and  fall  to  the  bottom  their  dead  bodies 
begin  to  putrefy,  and  the  putrefactive  bacteria  will  sooner 
or  later  master  the  acetic  bacteria. 

The  vinegar  in  which  the  mites  have  gained  the  upper 
hand  has  a  peculiar  yellowish  shade,  and  contains  what 
.appear  to  the  naked  eye  to  be  fine  white  specks. 

When  examined  under  the  microscope  these  have  the 
appearance  shown  in  Figs.  46  and  47. 

These  two  forms,  apparently  those  of  the  male  and 
iemale,  are  always  present.  They  appear  to  belong  to 
the  class  of  Sarcoptidce. 

When  once  vinegar  mites  have  become  established 
within  an  acetifier,  they  can  only  be  expelled  by  destroying 


ACETIFICATION    OF   THE   GYLE. 


127 


them  simultaneously  with  the  acetic  bacteria.  For  this 
purpose  the  vat  must  be  emptied,  and  the  interior  thor- 
oughly washed  with  hot  water,  then  well  fumigated  with 


Fig.  46.— Vinegar  Mite  (Bersch). 


Fig.  47.— Vinegar  Mite  (Bersch). 


128     VINEGAR  I    ITS   MANUFACTURE   AND   EXAMINATION. 

burning  sulphur  until  all  life  is  destroyed,  and  again 
washed.  It  is  then  recharged  with  gyle  and  a  little  crude 
vinegar  containing  the  bacteria,  but  it  will  be  some  time 
before  the  acetifier  gets  into  working  condition  again. 

The  Vinegar  Fly. — The  vinegar  fly  (Drosophila  funebris) 
is  of  very  common  occurrence,  and  may  be  observed  in 
any  vinegar  works  during  the  hotter  months  of  the  year. 
It  is  about  one-tenth  of  an  inch  in  length,  and  is  character- 
ised by  its  large  red  eyes,  red  thorax,  and  red  legs.  The 
abdomen  is  black  with  yellow  stripes,  and  the  wings  are 
somewhat  longer  than  the  body.  According  to  Brannt, 
the  larva  is  white,  has  twelve  segments  to  its  body,  and 
four  wart-like  structures  on  the  back.  After  eight  days 
it  is  transformed  into  a  yellow  chrysalis. 

Vinegar  makers  are  not  in  the  habit  of  paying  much 
attention  to  the  presence  of  the  vinegar  fly,  since,  so  far 
as  is  known,  it  does  not  in  any  way  affect  the  manu- 
facture, and  it  is  readily  prevented  from  becoming  a 
nuisance  by  keeping  the  works  thoroughly  clean  and 
not  allowing  any  spilt  vinegar  to  lie  about  upon  the 
ground. 


129 


CHAPTER  VIII. 
TREATMENT   OF  THE  CRUDE  VINEGAR. 

Filtration — Clarification — Action  of  Ferrocyanide — Sterilisation — Storage- 
Distillation — Composition  of  the  Residue  in  the  Still. 

Filtration  of  Vinegar. — After  leaving  the  acetifiers,  the 
crude  vinegar  is  pumped  into  store  vats,  where  it  is  allowed 
to  remain  for  several  weeks  or  months  to  mature.  During 
this  storage  period  it  deposits  albuminous  matter,  bac- 
terial cells,  etc.,  and  undergoes  partial  clarification. 
In  fact,  the  longer  the  vinegar  can  be  stored  the  more 
readily  can  it  subsequently  be  made  sufficiently  "  bright  " 
for  sending  out.  The  filters  used  in  vinegar  factories  are 
technically  known  as  "  rapes/'  owing  to  the  fact  that 
raisin  stalks  or  rapes  were  first  used  for  the  purpose  in 
the  seventeenth  century  (see  p.  6).  The  spent  raisin 
skins  left  as  a  residue  in  the  manufacture  of  British 
wines  are  still  sometimes  used  for  this  purpose,  although 
as  a  rule  the  filter  bed  is  generally  composed  of  other 
filtering  media,  such  as  beech  chips,  in  conjunction  with 
layers  of  shingle,  sand,  or  kieselguhr. 

Paper  pulp  is  also  used  for  filtering  vinegar,  and  has 
the  advantage  of  yielding  a  brilliant  filtrate,  although  it 
soon  becomes  clogged,  and  offers  difficulties  in  the  case 
of  vinegar  which  has  not  been  stored  for  a  long  time. 

The  general  appearance  of  the  inside  of  a  "  rape  " 
shed  is  shown  in  Fig.  48. 


130     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

The  large  vats,  each  of  which  takes  a  charge  of  about 
3,000  to  4,000  gallons,  are  arranged  in  rows  down  the 
sides  of  the  shed,  and  each  is  provided  with  its  own  pump, 
and  mains,  so  that  the  vinegar  can  be  pumped  into  any 
of  them  at  will. 

The  filtering  medium  is  supported  upon  a  false  bottom 
some  distance  up  within  the  vat,  so  that  a  vertical  section 
of  a  "  rape  "  shows  two  layers  of  liquid  separated  by  the 
filtering  medium. 

It  is  a  common  practice  for  the  "  rapes  "  to  be  worked 
in  groups.  The  vinegar  from  the  store  vats  is  introduced 
into  the  first  group,  and  is  there  continually  pumped 
over  and  over,  until  it  is  bright  enough  to  be  passed  on 
to  the  second  group  of  rapes.  There  the  same  process 
is  repeated  until  the  vinegar  is  nearly  brilliant,  and  the 
filtration  is  then  completed  in  the  third  group  of  rapes, 
which  should  yield  a  product  described  by  the  workmen 
as  "  candle-bright/' 

When  the  vinegar  has  been  brewed  from  a  low-dried 
malt,  or  when  much  raw  grain  has  been  used,  it  is  extremely 
difficult  to  remove  the  last  traces  of  suspended  matter, 
and  the  vinegar  will  continue  for  a  long  time  to  show  a 
characteristic  silken  opalescence,  which  might  escape 
notice  in  ordinary  daylight,  but  is  very  obvious  when 
the  bottle  is  held  up  to  an  artificial  light. 

Clarification  of  Vinegar. — The  persistent  cloudiness 
which  occurs  in  certain  vinegars  is  sometimes  more 
rapidly  removed  by  a  process  of  clarification  than  by 
filtration.  The  methods  employed  are  sometimes  mechani- 
cal and  sometimes  chemical.  In  the  first  case  an  in- 
soluble substance,  such  as  Spanish  earth  or  kieselguhr,  is 
stirred  up  with  the  vinegar,  and  as  it  subsides  it  carries 


TREATMENT   OF  THE   CRUDE   VINEGAR.  131 

clown  with  it  the  albuminous  particles  to  which  the 
turbidity  is  due. 

In  the  chemical  methods  the  albuminous  substances 
may  be  precipitated  by  the  addition  of  a "  gelatinous 
agent,  such  as  isinglass,  or  a  measured  quantity  of  a 
solution  of  potassium  ferrocyanide  may  be  added. 

Precipitation  with  Ferrocyanide. — This  reagent  will 
precipitate,  not  only  a  portion  of  the  nitrogenous  com- 
pounds, but  also  any  iron  in  the  vinegar,  and  the  vats 
in  which  the  precipitation  is  carried  out  are  usually 
stained  dark  blue  from  the  formation  of  Prussian  blue. 

It  is  essential,  however,  that  no  excess  of  ferrocyanide 
should  be  used,  and  on  more  than  one  occasion  vinegar 
containing  such  excess  has  caused  a  bright  blue  colour 
to  appear  in  pickles  which  had  been  preserved  in  brine 
containing  a  trace  of  iron. 

The  behaviour  of  potassium  ferrocyanide  in  vinegar 
was  investigated  by  Harden.*  It  was  found  that  the 
oxidation  which  took  place  spontaneously  in  an  aqueous 
solution  of  potassium  ferrocyanide  also  occurred  when  the 
salt  was  dissolved  in  dilute  (6  per  cent.)  acetic  acid,  a 
deposit  of  Prussian  blue  being  formed,  while  hydrocyanic 
acid  was  liberated  in  accordance  with  the  equation — 

7H4Fe(CN)6  +  02  =  24HCN  +  2H2O  +  Fe(CN)18. 

The  hydrocyanic  acid  thus  produced  disappeared  very 
slowly  from  the  acetic  acid,  the  amount  being  but  slightly 
reduced  after  the  liquid  had  stood  for  a  month. 

When,  however,  the  ferrocyanide  was  added  to  vinegar, 
some  further  reaction  apparently  took  place,  for  although 
the  deposit  of  Prussian  blue  was  obtained,  it  was  not 

*  Dr.  Hamill's  Report  to  L.G.B.,  1908,  p.  27. 


132      VINEGAR  I    ITS   MANUFACTURE   AND    EXAMINATION. 

possible  to  detect  hydrocyanic  acid  in  the  filtrate  from 
that  deposit.  Possibly  it  had  entered  into  combination 
with  the  aldehyde  of  some  other  constituent  of  the  vinegar, 
and  this  explanation  of  the  failure  to  detect  it  received 
support  from  the  results  of  experiments,  which  showed 
that  hydrocyanic  acid  did  actually  combine  with  some 
substance  in  vinegar  to  form  an  unstable  compound, 
which  was  decomposed  when  the  vinegar  was  heated. 

Although  no  definite  proof  was  obtained  of  the  forma- 
tion of  hydrocyanic  acid  when  an  excess  of  ferrocyanide 
was  added  to  vinegar,  the  evidence  pointed  to  its  pro- 
duction, and  justified  the  conclusion  that  such  vinegar 
should  be  looked  upon  with  suspicion. 

Sterilisation  of  Vinegar. — After  filtration  or  clarifica- 
tion, vinegar  will  still  contain  acetic  bacteria  or  their 
spores,  and  when  exposed  to  the  air  will  soon  become 
coated  with  a  zooglceal  film.  When  the  vinegar  is  sent 
out  in  casks,  and  the  consumers  allow  air  to  gain  access 
to  it,  by  not  replacing  the  spigot,  this  growth  of  the 
bacteria  will  occur  upon  the  surface  and  make  the  liquid 
turbid.  In  other  words,  the  casks  become  "  mothery." 
The  same  thing  happens  in  the  case  of  bottled  vinegar 
when  the  stopper  is  defective  and  allows  air  to  enter 
the  bottle. 

Long  continued  storage  of  the  vinegar  before  sending 
out  will  check  this  growth  of  "  mother/'  as  a  large  pro- 
portion of  the  bacteria  will  die  when  the  vinegar  is  kept 
for  some  months  in  a  well-closed  vat.  Want  of  space, 
however,  may  prevent  this  from  being  practicable  in 
many  cases,  and  at  best  it  is  not  as  effectual  as  sterilising 
the  vinegar. 

As    all    the    species    of    acetic    bacteria    perish    at    a 


TREATMENT   OF   THE  CRUDE   VINEGAR.  133 

relatively  low  temperature,  it  is  sufficient  to  heat  the 
vinegar  to  150°  F.,  to  insure  its  keeping,  even  when 
exposed  to  the  air,  since  the  acetic  acid  will  prevent  the 
development  of  micro-organisms  from  without.  This 
process  of  sterilisation  is  most  simply  effected  by  passing 
the  vinegar  through  a  coil  surrounded  by  a  tank  of 
water,  which  can  be  heated  by  steam  to  the  sterilising 
temperature.  On  leaving  this  heating  tank  the  vinegar 
is  passed  through  one  or  (preferably)  two  other  coils 
chilled  by  a  current  of  cold  water,  and  is  thus  cooled  down 
nearly  to  the  normal  temperature,  and  leaves  the  sterilising 
apparatus  without  any  appreciable  loss  of  acetic  acid. 

The  construction  of  the  steriliser  will  be  understood 
by  reference  to  the  accompanying  diagram,  in  which 
A  represents  the  feeding  tank  into  which  the  vinegar 
is  pumped,  to  give  it  sufficient  height  to  flow  through 
the  apparatus.  The  heating  tank  is  shown  at  B,  and 
the  cooling  tanks  at  C,  the  temperature  of  the  vinegar 
as  it  leaves -B  and  G  being  indicated  by  thermometers 
in  the  vinegar  main  at  the  points  e  and  /. 

The  flow  of  vinegar  is  regulated  by  the  cock  g,  until 
the  temperature  shown  at  the  point  e  is  not  less  than 
150°  F.  while  the  temperature  of  the  vinegar  leaving  the 
cooling  tank  should  not  exceed  70°  to  75°  F.  at  the  point  /. 

Sterilisation  in  this  way  causes  a  slight  deposition  of 
albuminous  matter  after  the  vinegar  has  stood  for  some 
time,  and  for  this  reason  it  is  advisable  to  run  the  sterilised 
vinegar  into  storage  vats,  and  to  leave  it  for  a  few  days 
before  bottling.  This  is  not  so  important  in  the  case  of 
cask  vinegar,  since  the  slight  deposit  will  not  be  notice- 
able, and  when  once  it  has  subsided  does  not  affect  the 
permanent  brightness  of  the  liquid. 


134      VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 


In  addition  to  its  action  in  improving  the  keeping 
qualities,  sterilisation  has  also  the  effect  of  maturing 
the  vinegar,  and  of  giving  a  softer  taste  and  less  acid 
aroma.  It  is  probable  that  this  is  due  to  its  promoting 
the  combination  of  the  residual  alcohol  in  the  vinegar 
with  the  acetic  acid,  and  thus  accelerating  the  forma- 


A,  Small  round  into  which 

vinegar  is  pumped. 

B,  Heating  cylinder. 

C,  Cooling  cylinder. 

D,  Steam  pipe. 

Fig.  49. — Diagram  of  Sterilising  Apparatus. 


E,  Cold  water  main. 

F,  Outlet  for  water. 

G,  Outlet  for  vinegar. 
T,  T,  Thermometers. 


tion  of    the  esters  to  which  matured  vinegar  owes  its 
flavour. 


o 
so 


TREATMENT  OF  THE  CRUDE   VINEGAR.  135 

Distillation  of  Vinegar. — The  early  method  of  distilling 
vinegar  to  obtain  aromatic  or  radical  vinegar  has  already 
been  described  (p.  63).  The  drawback  to  a  simple  dis- 
tillation at  the  ordinary  pressure  is  that  it  is  not  possible 
to  expel  the  acetic  acid  without  at  the  same  time  over- 
heating the  solid  matter  in  the  vinegar,  so  that  empy- 
reumatic  products  are  also  distilled.  Hence  the  early 
process  was  not  economical,  for  a  large  proportion  of 
the  acid  had  to  be  left  behind  with  the  residue  in  the 
still. 

In  the  modern  process  the  vinegar  is  distilled  at  a  lower 
temperature  under  reduced  pressure,  and  the  distillation 
can  then  be  carried  very  much  further  without  any  risk 
of  burning  the  solid  residue. 

The  small  stills  commonly  used  take  a  charge  of  about 
100  gallons  of  vinegar.  They  are  made  of  tin,  and  are 
heated  by  a  steam  jacket.  The  outlet  pipe  of  the  still 
is  connected  with  a  coil  immersed  in  a  tank  of  running 
water,  and  this  delivers  into  a  receiver,  in  which  is  a 
pipe  connected  with  a  vacuum  pump.  Distillation  is 
effected  at  a  reduced  pressure  of  15  to  20  inches,  and  is 
continued  until  the  still  contains  only  a  semi-solid  mass 
resembling  treacle.  Fig.  50  shows  one  of  the  vinegar 
stills  used  in  the  works  of  Messrs.  Beaufoy  &  Co. 

By  interrupting  the  distillation  at  definite  points  it 
is  possible  to  obtain  distillates  of  considerably  higher 
strength  than  the  original  vinegar.  For  example,  if  a 
6  per  cent,  vinegar  be  distilled,  the  first  third  of  the  dis- 
tillate will  contain  about  3  per  cent,  of  acetic  acid,  the 
second  third  about  5-5  per  cent.,  and  the  final  third 
between  9  and  10  per  cent. 

The   residue   will   also   retain   a   small   proportion   of 


136     VINEGAR  :    ITS    MANUFACTURE   AND    EXAMINATION. 


acetic  acid,  while  the  other  constituents  of  the  malt  and 
grain  will  be  present  in  a  concentrated  form.  The  still 
residue,  in  short,  is  a  dark  malt  extract,  slightly  acid, 
and  devoid  of  any  diastatic  capacity. 

Analyses   of   two   samples   of   still   residues   made   by 
Allen  *  gave  the  following  results  : — 


From  Barley 
Vinegar. 

From  Kice  and 
Grain  Vinegar. 

Per  cent. 

Per  cent. 

Total  solids,    .        *         .         .             - 

43-20 

72-30 

Ash,       .         .         .         .         . 

8-38 

9-21 

Alkalinity  of  ash  (K20),  .          .         „•' 

2-07 

1-40 

Phosphoric  acid, 

2-67 

0-24 

Nitrogen,        .         .         ..-.«' 

2-63 

2-63 

The  distillate  is  sold  under  the  names  of  distilled  malt 
vinegar,  white  vinegar,  and  white  wine  vinegar,  while  it 
has  been  held  by  a  Sheriff  in  Fife  that  distilled  malt 
vinegar  may  legally  be  sold  as  "  malt  vinegar/' 

*  Analyst,  1893,  xviii.,  241. 


137 


CHAPTER  IX. 
METHODS  OF  EXAMINATION. 

DETERMINATION  OF  ACIDITY — Automatic  Supply  Burette — Standardisation 
of  Alkali  Solutions — Salleron's  Ac6timetre — Otto's  Acetometer — 
Standards  of  Acidity — Crude  Pyroligneous  Acid — TOTAL  SOLIDS — 
Alkalinity  of  the  Ash — MINERAL  ACIDS — Detection — Determination 
— Combined  Sulphuric  Acid — Methyl-acetol — FORMIC  ACID — TOTAL 
NITROGEN — Nitrogenous  Compounds — PHOSPHORIC  ACID — INOSITOL 
IN  WINE  VINEGAR — COLOURING  MATTERS — Measurement  of  Colour 
Intensity — Lovibond's  Tintometer  —  Caramel  —  Cochineal  —  Archil — 
METALLIC  IMPURITIES — Iron — Copper — Lead— Tin — Arsenic — Official 
Method  of  Testing  for  Arsenic. 

Determination  of  Acidity. — The  acidity  of  most  ordinary 
vinegars  may  be  accurately  determined  by  titration  with 
standard  sodium  hydroxide  solution,  with  phenolphthalein 
as  indicator.  In  the  case  of  very  dark  samples  dilution 
is  necessary,  or  the  caramel  may  be  precipitated  with 
fuller's  earth,  and  an  aliquot  part  of  the  filtrate  titrated. 
"  Spotting  "  tests  with  litmus  paper  as  indicator  have 
been  shown  by  Erode  and  Lange  *  to  give  results  about 
1  per  cent,  lower  (in  terms  of  f  alkali  solution)  than 
direct  titration  with  phenolphthalein  as  indicator.  Hence, 
litmus  is  less  reliable  than  phenolphthalein  as  an  indicator 
for  vinegar. 

Where  numerous  samples  require  titrating  every  day, 
as  in  checking  the  working  of  acetifiers,  it  is  advisable 

*  Arbeit.  Kaiserl  Gesundheitsamt,  1909,  xxx.,  1. 


138     VINEGAR  :    ITS   MANUFACTURE   AND   EXAMINATION. 

to  use  a  special  stock  alkali  solution,  with  an  automatic- 
supply  burette,  wfth  a  guard  to  prevent  absorption  of 
carbon  dioxide. 

Standardisation  of  Alkali  Solutions. — The  most  rapid 
method  of  standardising  an  alkali  solution  is  by  the  use 
of  pure  oxalic  acid.  The  ordinary  "  pure  "  chemical 
usually  requires  further  purification  for  this  purpose. 
This  may  be  readily  effected  by  shaking  the  crystals 
with  warm  water  in  insufficient  quantity  to  dissolve 
them  completely,  filtering  the  solution,  and 
leaving  the  filtrate  to  crystallise.  The  new 
crop  of  crystals  is  dried  with  filter  paper  at 
the  ordinary  temperature,  and  kept  for  use 
as  an  original  standard. 

Salleron's  Ac6ti  metre. — The  instrument 
used  by  the  French  excise  officials  (and  by 
the  Customs  officers  in  Mauritius)  for  esti- 
mating the  acetic  strength  of  vinegar  is  a 
simple  glass  tube  closed  at  one  end  and 
graduated  into  divisions.  The  first  of  these, 
starting  from  the  bottom,  is  marked  with 
the  word  "  Vinaigre,"  and  indicates  the 
Fig.  51.  quantity  of  vinegar  (4  c.c.)  to  be  taken  for 

Salleron's          the  test 
Acetimetre.  .     . 

Ihis  quantity  ot  vinegar  is  introduced  by 
means  of  a  4  c.c.  pipette,  a  drop  of  phenolphthalein  solu- 
tion added,  and  then  successive  small  quantities  of  a 
standard  solution  of  sodium  hydroxide,*  the  tube  being 
closed  with  the  thumb  and  shaken  each  time  until  a 
permanent  pink  coloration  is  obtained  after  the  addition 

*  Twenty  c.c.  neutralise  4  c.c.  of  dilute  sulphuric  acid  (100  grammes  of 
monohydrated  acid  diluted  to  1,000  c.c.). 


METHODS    OF   EXAMINATION.  139 

of  a  single  drop.  The  strength  of  the  vinegar  may  then 
be  read  directly  upon  the  scale.  For  acids  above  25  per 
cent,  hi  strength  corresponding  dilution  is  necessary. 

An  instrument  of  a  similar  kind,  known  as  Otto's 
acetometer,  is  used  by  the  Customs  officials  in  Germany, 
while  a  more  accurate  tube  has  been  devised  by  Dujardin. 

This  method  of  determining  the  acidity  of  vinegar  is 
only  capable  of  giving  rough  estimations,  although,  on 
the  whole,  these  are  much  nearer  the  truth  than  the 
results  given  by  the  old  acetometer  of  the  British  Excise 
(p.  15). 

Standards  of  Acidity. — The  standard  for  the  minimum 
strength  of  vinegar  adopted  in  1877  by  the  Society  of 
Public  Analysts  has  already  been  mentioned  (p.  61). 
Although  this  limit  had  no  legal  sanction,  it  was  generally 
accepted  by  the  trade,  and  convictions  for  "  watering  " 
were  from  time  to  time  obtained  for  the  sale  of  vinegar 
containing  less  than  3  per  cent,  of  acetic  acid. 

In  May,  1912,  the  Local  Government  Board  recom- 
mended that  no  vinegar  or  artificial  vinegar  should  be 
sold  containing  less  than  4  per  cent,  of  acetic  acid. 

Since  the  Local  Government  Board  has  no  power, 
without  fresh  legislation,  to  fix  standards,  it  is  question- 
able whether  the  action  taken  by  certain  public  authori- 
ties against  the  vendors  of  weaker  vinegars  would  be 
supported  if  an  appeal  were  made  from  the  convictions 
obtained  in  several  instances. 

So  clearly  is  this  recognised  in  some  quarters  that 
certain  boroughs  have  refused  to  prosecute  the  vendors 
of  weak  vinegar,  and  have  urged  that  combined  action 
should  be  taken  in  petitioning  for  the  necessary  powers 
to  be  conferred  upon  the  Local  Government  Board. 


140      VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

Several  of  the  Colonies  have  fixed  limits  for  the  strength 
of  the  vinegars  which  may  be  sold  within  their  jurisdiction. 

The  question  of  strength  is  also  taken  into  account 
in  charging  duties  upon  vinegar  imported  into  the  different 
countries,  and  is  thus  frequently  brought  to  the  notice 
of  English  manufacturers. 

A  list  of  the  principal  Colonial  tariffs  for  vinegar  and 
acetic  acid  will  be  found  in  Appendix  I. 

Estimation  of  the  Strength  of  Pyroligneous  Acid. — The 
titration  of  crude  pyroligneous  acid  presents  considerable 
difficulty,  owing  to  the  deep  colour  of  the  liquid  preventing 
the  end-point  of  the  reaction  being  seen. 

The  strength  may  be  approximately  estimated  by 
Mohr's  method,  in  which  a  weighed  quantity  of  the  acid 
is  stirred  with  a  weighed  quantity  of  barium  carbonate 
until  effervescence  stops,  after  which  the  undissolved 
barium  salt  is  separated,  washed,  dried,  and  weighed. 
The  acids  will  correspond  to  the  amount  of  barium 
carbonate  dissolved,  and  are  calculated  as  acetic  acid. 
Or  the  undissolved  carbonate  may  be  determined  by 
titration  with  standard  nitric  acid. 

Total  Solid  Matter. — Usually  a  measured  quantity 
(10  c.c.)  of  the  vinegar  is  evaporated  on  the  water-bath 
with  frequent  shaking,  and  the  residue  dried  in  the 
water-oven  until  constant  in  weight.  The  shaking  of 
the  dish  during  the  evaporation  accelerates  the  expulsion 
of  the  acetic  acid,  which  is  obstinately  retained  by  the 
solid  matter.  Thus,  it  was  shown  by  Erode  and  Lange  * 
that  a  wine  vinegar  when  evaporated  without  shaking 
left  a  residue  of  0-79  per  cent,  containing  0-2  per  cent, 
of  acetic  acid,  while  when  the  dish  was  frequently  shaken 

*  Arbeit.  Kaiserl.  Gesundheittamte,  1909,  xxx.,  1. 


METHODS   OF   EXAMINATION.  141 

the  residue  was  0-64  per  cent.,  and  contained  only  0-08  per 
cent,  of  acid. 

In  any  case,  titration  of  the  acidity  of  the  residue  and 
deduction  of  the  result  from  the  amount  obtained  by 
weighing  is  a  necessary  correction. 

An  approximate  estimation  of  the  total  solids,  accur- 
ate within  about  0-1  per  cent.,  may  be  rapidly  made  by 
titrating  the  acidity,  and  determining  the  specific  gravity 
of  the  vinegar  at  15°  C.  by  means  of  a  standard  Bates* 
saccharometer. 

From  the  specific  gravity  thus  indicated  the  amount 
corresponding  to  the  acetic  acid  strength  at  15°  C.  is 
found  by  reference  to  Oudemanns'  table  (p.  75). 

The  difference  will  show  the  specific  gravity  due  to  the 
solid  extract  from  the  wort,  and  the  amount  of  the  latter 
may  be  found  by  reference  to  the  subjoined  table  (p.  142), 
which  is  abridged  from  Schultze's  long  table. 

The  following  example  may  be  given  by  way  of  illus- 
tration :— 

A  sample  of  malt  vinegar  had  a  specific  gravity  of 
1-014  at  15°  C.  and  an  acidity  of  4-5  per  cent.  This 
degree  of  acetic  acid  corresponds  to  a  specific  gravity  of 
1-006 ;  while  the  specific  gravity  due  to  the  solid  extract  is 
10-14  —  0-006  =  1-008.  A  specific  gravity  of  1-008  repre- 
sents 2-09  per  cent,  of  total  solids  in  Schultze's  table,  while 
the  amount  determined  by  evaporation  was  2-07  per  cent. 

Alkalinity  of  the  Ash. — In  some  cases  an  indication  of 
the  probable  origin  of  a  vinegar  may  be  obtained  by 
determining  the  alkalinity  of  the  ash,  since  in  a  vinegar 
brewed  from  glucose  the  mineral  acid  used  for  the  hydro- 
lysis will  have  combined  with  part  of  the  bases,  and  thus 
cause  the  proportion  of  potassium  oxide  to  be  low. 


142    VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 


SCHULTZE'S  EXTRACT  TABLE. 


Specific 
Gravity  at 

15  C.C. 

Extract  in 
100  Griris. 

Extract  in 
100  c.c. 

Specific 
Gravity  at 
15  c.c. 

Extract  in 
100  Grms. 

Extract  in 
100  c.c. 

Grins. 

Grms. 

Grins. 

Grms. 

1-0001 

0-03 

0-03 

1-0125 

3-23 

3-27 

1-0005 

0-13 

0-13 

1-0128 

3-30 

3-34 

1-0010 

0-26 

0-26 

1-0130 

3-35 

3-39 

1-0015 

0-39 

0-39 

1-0133 

3-43 

3-48 

1-0020 

0-52 

0-52 

1-0135 

3-48 

3-53 

1-0025 

0-66 

0-66 

1-0138 

3-56 

3-61 

1-0030 

0-79 

0-79 

1-0140 

3-61 

3-66 

1-0035 

0-92 

0-92 

1-0143 

3-69 

3-74 

1-0040 

1-05 

1-05 

1-0145 

3-74 

3-79 

1-0045 

1-18 

•19 

•0148 

3-82 

3-88 

1-0050 

•31 

•32 

•0150 

3-87 

3-93 

1-0055 

•44 

•45 

•0153 

3-95 

4-01 

1-0060 

•56 

•57 

•0155 

4-00 

4-06 

1-0065 

•69 

•70 

•0158 

4-08 

4-14 

1-0070 

•82 

•83 

•0160 

4-13 

4-20 

1-0075 

•95 

•96 

1-0163 

4-21 

4-28 

1-0080 

2-07 

2-09 

1-0165 

4-26 

4-33 

1-0085 

2-20 

2-22 

1-0168 

4-34 

4-41 

1-0090 

2-33 

2-35 

1-0170 

4-39 

4-46 

1-0095 

2-46 

2-48 

1-0173 

4-47 

4-55 

1-0100 

2-58 

2-68 

1-0175 

4-53 

4-61 

1-0105 

2-71 

2-74 

1-0180 

4-66 

4-74 

1-0110 

2-84 

2-87 

1-0185 

4-79 

4-88 

1-0115 

2-97 

3-00 

1-0190 

4-93 

5-02 

1-0120 

3-10 

3-14 

In  the  United  States'  official  definition  of  malt  vinegar 
it  is  enacted  that  the  ash  from  100  c.c.  of  the  sample 
shall  require  for  its  neutralisation  not  less  than  4  c.c. 
of  decinormal  acid. 

Actual  determination  of  the  potassium  oxide 
as  practised  by  Tatlock  usually  affords  a  more 
satisfactory  criterion  than  the  titration  of  the 
.ash. 

The  variations  in  this  figure  in  different  kinds  of  vinegar 


METHODS    OF   EXAMINATION. 


143 


may   be   illustrated   by   the   following   results   given   by 
Allen  *  :— 


/ 

Grain  and  Malt. 

Grain  and  Sugar. 

Rice. 

Sugar. 

Alkalinity  as  KoO^j 
per  100  parts  of  j- 
vinegar, 

0-091  to  0-118 

0-03 

0-013 

traces 

DETECTION  OF  FREE  MINERAL  ACIDS. 

Hilger's  Method. — Free  mineral  acids  in  vinegar  may 
be  detected  by  means  of  a  solution  of  methyl  violet 
(0-1  grm.  per  1,000  c.c.),  which  is  not  affected  by  acetic 
or  other  organic  acids,  but  is  changed  to  blue  or  green 
by  mineral  acids.  The  test  is  best  applied  by  adding 
4  to  5  drops  of  the  reagent  to  20  c.c.  of  the  vinegar, 
shaking  the  tube  and  comparing  the  colour  with  that 
obtained  with  dilute  acetic  acid  coloured  to  the  same 
intensity  with  caramel. 

Congo-red  paper  is  also  useful  as  a  preliminary  test, 
being  changed  to  blue  by  free  mineral  acids,  though  it  is 
not  affected  by  acetic  acid. 

DETERMINATION  OF  MINERAL  ACIDS. 

Hilger's  Method. — Twenty  c.c.  of  the  vinegar  are  neut- 
ralised with  N/alkali  solution,  with  turmeric  paper  as 
indicator,  and  evaporated  to  about  2  c.c.,  and  the  residue 
is  mixed  with  a  few  drops  of  a  0-01  per  cent,  solution  of 
methyl  violet  2  B  and  4  c.c.  of  water.  The  liquid  is 
heated  to  boiling  point,  and  titrated  with  N/sulphuric 
acid  until  the  colour  changes  to  blue  or  greerr.  It  is 

*  Analyst,  1894,  xix.,  15. 


144     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

advisable  to  compare  the  change  of  colour  with  that 
given  by  an  aqueous  solution  of  the  methyl  violet  con- 
taining about  the  same  quantity  of  caramel  as  the  vinegar 
in  question. 

The  difference  between  the  number  of  c.c.  of  N /alkali 
solution  originally  used  and  the  number  of  c.c.  of  sulphuric 
acid  required  in  the  last  titration  corresponds  to  the 
amount  of  free  mineral  acids  present.  The  result  multi- 
plied by  1-225  gives  the  percentage  in  terms  of  sulphuric 
acid. 

FREE  SULPHURIC  ACID  IN  VINEGAR. 

The  amount  of  free  sulphuric  acid  (0-1  per  cent.)  which 
was  expressly  permitted  to  be  added  to  vinegar  by  the 
Act  of  George  III.  of  1818  was  often  considerably 
exceeded.  Thus,  in  the  year  1852,  a  body  of  Commis- 
sioners appointed  by  the  Lancet  *  examined  27  samples 
of  vinegar  typical  of  the  products  of  the  principal  manu- 
facturers in  this  country.  The  samples  of  only  two 
makers  were  found  to  be  quite  free  from  sulphuric  acid, 
while  the  others  contained  from  0-63  to  6-02  parts  per 
1,000. 

These  figures,  however,  included  sulphuric  acid  present 
in  the  form  of  sulphates,  the  proportion  of  combined 
acid  ranging  from  0-44  to  0-39  part  per  1,000,  so  that 
many  of  the  samples  were  well  within  the  legal  limit 
for  free  acid. 

At  the  present  time  it  is  improbable  that  any  manu- 
facturer in  this  country  adds  free  sulphuric  acid  to  his 
vinegar,  although,  as  may  be  gathered  from  Muspratt's  f 

*  Lancet,  Aug.  28,  1852. 
f  Dictiowry  of  Chemistry,  1860,  p.  16. 


METHODS   OF  EXAMINATION.  145 

account,  the  practice  died  very  slowly.  It  is  perhaps 
hardly  necessary  to  add  that  vinegars  of  sufficient  acetic 
strength  will  keep  quite  well  without  any  such  addition. 

Hehner's  Method. — A  method  of  detecting  and  esti- 
mating free  sulphuric  acid  and  other  mineral  acids  in 
vinegar  was  based  by  Hehner  *  upon  the  fact  that 
potassium  and  sodium  acetates  (or  tartrates)  are  always 
present  in  vinegar.  If  a  small  amount  of  a  mineral  acid 
is  added,  it  will  decompose  a  corresponding  quantity  of 
acetate  or  tart  rate,  with  the  liberation  of  the  organic 
acid,  but  if  added  in  excess  of  the  corresponding  quantity 
of  organic  salts  this  excess  will  remain  as  a  free  acid. 
Hence,  vinegars  that  contain  acetates  or  tartrates  cannot 
contain  a  free  mineral  acid,  and  since  on  igniting  these 
organic  salts  they  are  decomposed  into  carbonates,  an 
examination  of  the  ash  of  the  vinegar  may  afford  an 
indication  of  the  presence  of  free  mineral  acid. 

If  the  ash  is  alkaline,  it  is  probable  that  no  free  mineral 
acid  has  been  present  in  the  vinegar,  although  a  quantity 
insufficient  to  decompose  the  whole  of  the  acetates  or 
tartrates  might  originally  have  been  added,  and  it  is 
possible  for  calcium  sulphates  or  other  calcium  salts  to 
be  decomposed  in  the  ignition,  and  to  render  the  ash 
alkaline  ;  but  if  the  ash  is  neutral  the  presence  of  free 
mineral  acid  is  probably  indicated. 

Estimation  of  Free  Acid. — Hehner 's  method  will  also 
give  quantitative  results.  Fifty  c.c.  of  the  vinegar  are 
evaporated  with  25  c.c.  of  •—  sodium  hydroxide  solution, 
and  the  residue  charred  at  a  low  temperature,  mixed 
with  25  c.c.  of  -g-  sulphuric  acid,  boiled,  filtered,  and 
washed.  The  filtrate  is  titrated  with  |>  sodium  hydroxide 

*  Analyst,  1877,  i.,  105. 

10 


146     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

solution,  with  litmus  or  cochineal  as  indicator.  The 
number  of  c.c.  of  alkali  required  corresponds  to  the  free 
mineral  acid. 

Owing  to  the  necessity  of  repeating  the  estimation  if 
the  amount  of  alkali  originally  added  was  insufficient, 
Allen  and  Bodmer  *  modified  the  test  by  neutralising 
the  whole  of  the  acid  present  in  the  vinegar  prior  to  the 
evaporation. 

In  the  case  of  vinegars,  such  as  those  derived  from  malt 
or  grain,  which  contain  a  large  proportion  of  phosphate, 
it  is  necessary  to  take  into  consideration  the  fact  that 
any  phosphoric  acid  liberated  in  the  test  will  react  with 
alkali  (methyl-orange  as  indicator)  in  a  different  way  than 
hydrochloric  or  sulphuric  acid.  The  importance  of  this 
point  has  been  emphasised  by  Richardson  and  Bo  wen.  j- 

On  boiling  potassium  phosphate,  K3P04,  with  a  definite 
excess  of  sulphuric  acid,  potassium  sulphate  and  phos- 
phoric acid  are  produced,  but  on  titrating  the  excess  of 
sulphuric  acid,  different  results  are  obtained  when  methyl- 
orange  and  phenolphthalein  are  used  as  indicators. 

The  end  point  of  the  reaction  is  reached,  with  methyl- 
orange  as  indicator,  when  dihydrogen  potassium  phos- 
phate has  been  formed — i.e.,  only  one- third  of  the  phos- 
phoric acid  present  is  shown.  On  now  adding  phenol- 
phthalein the  titration  can  be  continued  until  dipotassium 
hydrogen  phosphate  is  formed,  accounting  for  another 
third  of  the  phosphoric  acid. 

Richardson  and  Bowen's  Method. — Based  upon  these 
considerations,  Richardson  and  Bowen  (loc.  cit.)  have 
devised  the  following  process,  which  estimates,  not  only 

*  Analyst,  1878,  iii.,  268. 

t  J.  Soc.  Chem.  Ind.,  1906,  xxv.,  836. 


METHODS    OF   EXAMINATION.  147 

the  sulphuric  acid  present  as  such,  but  also  the  phosphoric 
acid  liberated  from  the  phosphates  by  the  sulphuric  acid. 
Although  part  of  the  phosphoric  acid  is  present  as  calcium 
phosphate,  no  material  error  is  introduced  by  basing  the 
calculation  upon  potassium  phosphate. 

Twenty-five  c.c.  of  the  vinegar  are  evaporated  to 
dry  ness  with  25  c.c.  of  ^r  sodium  hydroxide  solution, 
and  the  residue  charred  at  a  temperature  insufficient  to 
fuse  the  ash.  The  black  mass  is  cooled,  treated  with 
hydrogen  peroxide  (to  prevent  liberation  of  hydrogen 
sulphide),  and  boiled  with  50  c.c.  of  -g-  sulphuric  acid. 
The  filtrate  and  washings  are  titrated  with  ^-  sodium 
hydroxide  solution  with  methyl-orange  or  lacmoid  (pre- 
ferably the  latter)  as  indicator.  The  liquid  is  then  boiled 
with  a  few  drops  of  -—•  sulphuric  acid  to  expel  carbon 
dioxide,  the  acid  neutralised  with  -j$-  alkali  solution,  and 
the  titration  with  -^-  sodium  hydroxide  solution  com- 
pleted after  the  addition  of  phenolphthalein. 

To  account  for  the  remaining  third  of  unneutralised 
phosphoric  acid  twice  the  number  of  c.c.  of  standard 
alkali  used  in  the  final  titration  are  taken  for  the  calcu- 
lation. 

The  results  obtained  by  this  method,  and  by  Hehner's 
method  with  vinegars  containing  known  quantities  of 
added  sulphuric  acid,  were  as  given  in  table  on  p.  148. 

The  difference  between  the  two  sets  of  results  was 
attributed  to  the  influence  of  the  carbon  dioxide  on  the 
methyl-orange,  which  caused  the  results  to  be  too  high. 

By  this  method  of  Richardson  and  Bowen  the  amount 
of  sulphuric  acid  originally  added  is  shown,  whereas 
Hehner's  method  gives  that  actually  present  in  the 
vinegar  at  the  time  of  analysis. 


148     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 


Sulphuric  Acid 
Added. 

With  Methyl  Orange. 

With  Lacmoid. 

Hehner's 
Method. 

Richardson 
and  Bowen's 
Method. 

Hehner's 
Method. 

E-ichardson 
and  Bowen's 
Method. 

Per  cent. 
A,  0-098, 
B,  0-049, 
C,  nil,       . 

Per  cent. 
+  0-033 
-  0-033 

-  0-080 

Per  cent. 
+  0-099 
+  0-064 
+  0-023 

Per  cent. 
+  0-0216 
-  0-045 
-  0-098 

Per  cent. 
+  0-099 
+  0-045 
-f  0-004 

Combined  Sulphuric  Acid. — The  proportion  of  sulphuric 
acid  in  the  form  of  sulphates  in  vinegar  varies  consider- 
ably, as  will  be  seen  from  the  following  analyses,  made 
by  the  writer,  of  the  vinegars  of  six  of  the  leading  manu- 
facturers : — 


A,  0-03  per  cent. 

B,  0-10 

C,  0-032       „ 


D,  0-155  per  cent. 

E,  0-170 

F,  0-021 


The  vinegars  B,  D,  and  E  were  made  by  the  inversion 
process,  while  the  other  three  were  mash- tun  products. 

An  attempt  was  made  some  years  ago  to  condemn 
vinegars  containing  more  than  0-03  per  cent,  of  combined 
sulphuric  acid,  and  several  prosecutions  were  initiated.* 

Although  the  amount  of  combined  sulphuric  acid 
affords  evidence  that  the  vinegar  was  made  by  inversion 
of  starch  with  sulphuric  acid,  it  is  not  an  infallible  proof, 
for  an  amount  of  sulphate  in  excess  of  0-03  per  cent, 
might  be  also  due  to  the  use  of  a  very  hard  water,  or  to 
sulphuring  the  casks,  or  washing  them  with  a  soluble 

*  Dr.  Edmunds,  Public  Analyst  for  St.  James',  writing  in  the  British 
Food  Journ.  (1900,  p.  21),  stated  that  he  regarded  all  vinegars  containing 
more  than  0-0 1  to  0-03  per  cent,  of  sulphates  as  adulterated. 


METHODS   OF   EXAMINATION.  149 

sulphite,   which  had    subsequently  become    oxidised  to 
sulphate. 

OTHER   CONSTITUENTS. 

Detection  of  Methyl- Acetol. — It  has  been  shown  by 
Pastureau  *  that  certain  vinegars  contain  methyl-acetol, 
CH3 .  CO  .  CHOH  .  CH3,  probably  derived  from  wood 
acid.  It  may  be  isolated  by  neutralising  100  c.c.  of  the 
sample  with  sodium  hydroxide,  and  distilling  the  liquid 
to  dryness. 

If  methyl-acetol  is  present,  the  distillate  will  reduce 
cold  Fehling's  solution,  and  when  treated  with  iodine 
will  give  a  precipitate  of  iodoform.  When  treated  with 
phenyl-hydrazine  acetate  it  will  yield  an  osazone  melting 
at  243°  C.,  and  giving  a  red  coloration  when  dissolved 
in  ether-alcohol  and  tested  with  ferric  chloride,  and  red 
crystals  on  evaporating  the  liquid. 

A  quantitative  estimation  may  be  made  by  treating 
an  aliquot  part  of  the  distillate  with  a  few  drops  of  sodium 
hydroxide  solution  and  ammonia,  and  adding  10  c.c.  of 
£  silver  nitrate  solution.  The  liquid  is  allowed  to  stand 
for  24  hours,  diluted  to  100  c.c.,  and  filtered,  and  the 
excess  of  silver  titrated  by  the  cyanide  method. 

From  the  amount  of  reduced  silver  the  quantity  of 
methyl-acetol  is  calculated  by  means  of  the  equation — 

3(CH3CO  .  CHOH  .  CH3)  +  AgN03 

=  3CH3CO  .  COCH3  +  3H20  +  Ag. 

One  sample  of  vinegar  thus  examined  contained  0-32  per 
cent,  of  methyl-acetol.  Or  Kling's  method  f  of  estimation 

*Journ.  Pharm.  Chim.,  1905,  [6],  xxi.,  593. 
f  Bull.  Soc.  Chim.,  1906,  xxv.,  215. 


150     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

with  alkaline  copper  solution  may  be  used,  each  gramme 
of  methyl-acetol  yielding  2-85  grammes  of  cuprous 
oxide. 

Estimation  of  Formic  Acid. — Fincke  *  has  devised  the 
following  method  of  estimating  formic  acid  in  vinegar  : — 
Five  c.c.  of  the  sample  are  heated  for  two  hours  on  the 
water  bath  beneath  a  reflux  condenser  with  5  grms.  of 
sodium  acetate,  40  c.c.  of  a  5  per  cent,  mercuric  chloride 
solution  and  30  c.c.  of  water,  the  liquid  in  the  flask  being 
completely  immersed  in  the  boiling  water.  The  resulting 
precipitate  of  calomel  is  collected  in  a  Gooch's  crucible, 
washed  with  water,  alcohol  and  ether,  and  dried  and 
weighed.  The.  weight  multiplied  by  the  factor  0-0977 
gives  the  amount  of  formic  acid. 

The  method  affords  an  indication  of  the  presence  of 
added  acetic  acid  in  some  vinegars,  since  commercial 
acetic  acid  almost  invariably  contains  formic  acid  as  an 
impurity.  It  is  essential,  however,  that  no  caramelised 
sugar  should  be  present,  for  sugar  yields  appreciable 
quantities  of  formic  acid  when  heated  to  160°  C.,  at 
which  temperature  caramelisation  begins. 

Hence,  as  caramel  is  universally  employed  for  colouring 
fermentation  vinegars  in  this  country,  no  reliance  can 
be  placed  upon  the  results  of  the  formic  acid  test  if  applied 
to  coloured  vinegars. 

Moreover,  although  formic  acid  does  not  appear  to  be 
produced  in  the  manufacture  of  spirit  vinegar,  it  is 
found  as  a  normal  constituent  in  wine  vinegars,  f  and 
probably  also  in  other  kinds  of  vinegar  to  which  no 
caramel  has  been  added. 

*J.  Soc.  Chem.  Ind.,  1911,  xxx.,  82,  235,  916. 
f  Analyst,  1911,  xxxvi.,  496. 


METHODS   OF   EXAMINATION.  151 

Determination  of  Total  Nitrogen. — The  nitrogenous 
substances  in  malt  are  readily  transformed  into  am- 
monium sulphate  by  Kjeldahl's  process,  and  a  clear 
solution  may  be  obtained  in  about  an  hour  by  adding 
a  little  potassium  bisulphate  to  the  sulphuric  acid.  The 
addition  of  mercury  accelerates  the  process,  but,  as  a 
rule,  is  not  necessary.  From  10  to  25  c.c.  of  the  vinegar 
are  used  for  the  determination. 

Nature  of  Nitrogenous  Substances. — Only  a  small  pro- 
portion of  the  nitrogen  in  vinegar  appears  to  be  in  the 
form  of  ammonium  salts  or  albumoses  precipitable  by 
ammonium  or  zinc  sulphates.  In  one  experiment  in 
which  1,000  c.c.  of  vinegar  brewed  from  barley  malt 
were  concentrated  to  100  c.c.,  and  aliquot  portions  used 
for  the  different  estimations,  the  following  results  were 
obtained  by  the  writer  :— 

Per  cent. 

Total  nitrogen, 0-1204 

Nitrogen   in  precipitate  given   by"| 

ammonium  sulphate  (after  evapo- 1(1)  0-0127 

ration   with   water   and  barium  |  (2)  0-0157 
carbonate),                                       J 

Nitrogen  in  zinc  sulphate  precipitate,    .  0-0148 

Ammoniacal  nitrogen,          .  -        .          .  0-015 

Similar  results  were  obtained  with  a  sample  of  com- 
mercial malt  vinegar  :— 

Per  cent. 

Total  nitrogen,  .          .  .          .<        .  •  0-089 

Nitrogen   precipitated  by    ammonium 

sulphate,         .       ' .  .         .          .  0-008 

Ammoniacal  nitrogen,  .          .         .  0-007 


152     VINEGAR  I    ITS   MANUFACTURE   AND    EXAMINATION. 

Determination  of  Phosphoric  Acid. — Of  the  many 
processes  devised  for  determining  small  quantities  of 
phosphoric  acid,  one  of  the  most  simple  and  accurate 
for  the  analysis  of  vinegar  is  the  modification  of  the 
molybdate  method  devised  by  Hehner. 

The  ash  from  10  c.c.  of  the  sample  is  dissolved  in  the 
smallest  possible  quantity  of  dilute  nitric  acid,  and 
treated  with  a  large  excess  of  an  ammonium  molybdate 
solution.  The  basin  is  allowed  to  stand  for  12  hours 
at  the  ordinary  temperature,  or  for  two  hours  on 
the  top  of  a  hot- water  oven,  after  which  the  yellow 
precipitate  is  washed  twice  by  decantation  with  cold 
water.  It  is  then  dissolved  in  ammonia  solution,  the 
liquid  evaporated,  and  the  residue  dried  on  the  water 
bath.  The  weight  divided  by  the  factor  28-5  gives  the 
amount  of  phosphoric  acid  (P205). 

The  molybdate  reagent  may  be  prepared  by  dissolving 
50  grms.  of  molybdic  acid  in  a  mixture  of  50  c.c.  of 
ammonia  solution  and  150  c.c.  of  water.  When  cold, 
the  solution  is  cautiously  added  to  a  cold  mixture  of 
280  c.c.  of  nitric  acid  and  470  c.c.  of  water,  and  the 
reagent  is  filtered  after  standing  for  some  hours. 

As  a  rule,  the  amount  of  phosphoric  acid  in  a  vinegar 
brewed  from  malted  or  unmalted  barley  will  exceed 
0-05  per  cent.,  but  the  amount  may  be  increased  by  the 
use  of  yeast  foods  to  aid  the  fermentation,  or  may  be 
reduced  by  clarification  processes  in  which  the  wort  is 
fined  by  the  addition  of  soluble  calcium  salts. 

Reducing  Sugars. — The  following  method  of  estimating 
the  reducing  sugars  in  cider  vinegar  is  recommended 
by  Leach  and  Lythgoe*  : — Two  portions  (25  c.c.  each) 

*./.  Amer.  Chem.  »Sroc.,  1904,  xxvi.,  375. 


METHODS    OF   EXAMINATION.  153 

are  taken.  One  is  diluted  with  20  c.c.  of  water  and  heated 
with  5  c.c.  of  hydrochloric  acid  for  ten  minutes,  and  then 
cooled.  Both  portions  are  neutralised  with  sodium 
hydroxide  and  made  up  to  100  c.c.,  and  tested  with 
Fehling's  solution.  The  amount  of  reducing  sugars 
ought  to  be  the  same  before  and  after  inversion,  any 
increase  denoting  the  presence  of  cane  sugar. 

The  ratio  between  the  weights  of  total  solids  and 
dextrose  affords  a  means  of  detecting  glucose  vinegars 
in  wine  vinegars  (see  p.  187). 

Detection  of  Inositol  in  Wine  Vinegar. — It  has  been 
shown  by  Meillere  *  that  inositol  is  a  constituent  of  all 
wines,  and  since  this  sugar  is  not  decomposed  during 
acetic  fermentation,  its  separation  and  identification 
affords  a  means  of  distinguishing  between  wine  vinegar 
and  spirit  vinegar. 

The  following  method  of  applying  the  test  was  devised 
by  Fleury  •(•  : — One  hundred  c.c.  of  the  vinegar  are  evapo- 
rated nearly  to  dryness,  and  the  residue  taken  up  with 
50  c.c.  of  water,  neutralised  with  sodium  hydroxide,  and 
ground  up  with  3  grms.  of  barium  hydroxide.  The  pre- 
cipitate is  separated,  with  the  aid  of  centrifugal  force, 
and  washed  with  20  to  30  c.c.  of  baryta  water,  and  the 
filtrate  and  washings  freed  from  barium  by  means  of  a 
current  of  carbon  dioxide,  after  which  10  c.c.  of  dilute 
lead  acetate  solution  are  added,  and  the  new  precipitate 
separated  as  before.  The  filtrate  is  concentrated  to 
100  c.c.,  and  treated  with  10  c.c.  of  the  official  basic  lead 
acetate  solution  (lead  acetate,  300  grms.  ;  lead  oxide, 
100  grms.  ;  water,  700  c.c.,  shaken  and  filtered),  and 

*  Journ.  Pharm.  Chim.,  1908,  [6],  xxviii.,  289. 
t  Ibid.,  1910,  [7],  ii.,  264. 


154     VINEGAR  :    ITS   MANUFACTURE   AND   EXAMINATION. 

2  grms.  of  neutral  cadmium  acetate  in  solution.  The 
precipitate  containing  the  inositol  is  washed  and  decom- 
posed with  hydrogen  sulphide,  and  nitrate  from  the 
cadmium  sulphide  is  concentrated  to  a  syrup,  and  treated 
with  20  c.c.  of  absolute  alcohol  and  5  c.c.  of  anhydrous 
ether,  and  allowed  to  stand  for  24  hours.  The  crystals 
of  inositol  which  form  in  the  case  of  a  wine  vinegar  are 
separated  and  identified. 

Tests  of  identity  have  been  based  upon  the  oxidation 
of  the  sugar  into  a  quinonic  compound,  rhodizonic  acid, 
some  of  the  salts  of  which  are  of  a  bright  red  colour. 

Seidel  dissolves  a  little  of  the  precipitate  in  water,  and 
treats  the  solution  with  a  drop  of  Millon's  reagent.*  The 
liquid  is  evaporated  to  dryness,  the  residue  dried  at 
110°  to  120°  C.,  and  treated  with  3  c.c.  of  glacial  acetic 
acid,  and  one  drop  of  a  10  per  cent,  solution  of  strontium 
acetate,  and  the  solution  evaporated  on  the  water  bath. 
A  bright  red  coloration  and  deposit  are  obtained. 

Another  proof  of  identity  is  to  evaporate  the  residue 
with  Gallois'  mercuric  reagent,  which  is  prepared  by 
dissolving  1  grm.  of  yellow  mercury  oxide  in  a  mixture 
of  1  c.c.  of  nitric  acid  and  10  c.c.  of  water,  and  diluting 
the  solution  to  20  c.c.  The  resulting  mercury  rhodizonate 
is  a  brilliant  red  salt. 

Detection  of  Malic  Acid. — Cider  vinegar  should 
always  contain  malic  acid,  and  the  following  tests  for 
its  detection  are  recommended  by  Leach  and  Lythgoe  f  : 
— The  vinegar  should  give  a  precipitate  with  lead  acetate, 

*  One  part  of  mercury  is  dissolved  in  2  parts  of  nitric  acid  (40°  B.),  and 
the  solution  diluted  with  an  equal  volume  of  water,  and  after  24  hours 
decanted  from  the  crystalline  deposit. 

f  J.  Amer.  Ckem.  Soc.,  1904,  xxvi.,  375. 


METHODS    OF   EXAMINATION.  155 

subsiding  rapidly.  The  presence  of  malic  acid  is  then 
confirmed  by  treating  5  c.c.  of  the  vinegar  with  1  c.c.  of 
10  per  cent,  calcium  chloride  solution,  filtering,  and  adding 
3  volumes  of  95  per  cent,  alcohol  to  the  filtrate.  A  floc- 
culent  precipitate  will  be  obtained  if  malic  acid  be  present. 

The  addition  of  the  alcohol  will  also  precipitate  dextrin, 
but  this  may  be  detected  by  a  dextro-rotatory  reading 
in  the  polarimetric  test. 

A  precipitate  should  also  be  obtained  with  calcium 
sulphate  after  drying  the  calcium  chloride  precipitate, 
dissolving  it  in  nitric  acid,  and  evaporating  the  solution 
on  the  water  bath  to  convert  the  calcium  malate  into 
calcium  oxalate,  which  is  then  decomposed  by  boiling 
with  sodium  carbonate.  The  filtrate  from  the  calcium 
carbonate  is  then  acidified  with  acetic  acid,  and  tested 
with  calcium  sulphate  solution. 

Tartaric  Acid. — If  the  total  solids  left  on  evaporation 
of  wine  vinegar  be  treated  with  absolute  alcohol,  a 
granular  residue  of  hydrogen  potassium  tartrate  will  be 
left  undissolved.  The  nature  of  this  deposit  may  be 
confirmed  by  dissolving  it  in  the  smallest  possible  quantity 
of  hot  water,  and  stirring  the  solution  in  a  watch-glass 
by  means  of  a  glass  rod.  The  cream  of  tartar  will  then 
be  re-deposited  in  streaks  following  the  lines  of  the  rod. 

The  following  confirmatory  test  of  identification, 
devised  by  Deniges,  may  also  be  applied  : — The  crystals 
are  added  to  a  reagent  consisting  of  3  c.c.  of  sulphuric 
acid  and  3  drops  of  a  solution  of  resorcinol  (2  grms.  in 
100  c.c.  of  water  acidulated  with  5  c.c.  of  sulphuric  acid), 
and  the  mixture  heated  to  130°  to  140°  C.  In  the  presence 
of  tartaric  acid  an  intense  carmine-red  coloration  is 
produced. 


156     VINEGAR  :    ITS   MANUFACTURE    AND    EXAMINATION. 

For  the  estimation  of  the  potassium  bitartrate  25  c.c. 
of  the  vinegar  are  evaporated  to  a  syrup.  This  is  dissolved 
in  25  c.c.  of  water,  and  the  solution  mixed  with  100  c.c. 
of  alcohol-ether  (1  :  1),  and  allowed  to  stand  for  24  hours 
in  a  cool  place.  The  resulting  precipitate  is  washed  with 
alcohol-ether,  and  dissolved  in  hot  water,  and  the  solu- 
tion titrated  with  ~  alkali.  Each  c.c.  required  corre- 
sponds to  0-0188  grm.  of  potassium  bitartrate. 

Citric  Acid. — This  may  be  detected  by  the  test  devised 
by  Deniges  for  wines  : — Ten  c.c.  of  the  vinegar  are 
shaken  with  1  grm.  of  lead  peroxide  and  2  c.c.  of  mercuric 
sulphate  solution,  and  filtered.  About  5  c.c.  of  the 
filtrate  are  boiled  and  treated  with  a  drop  of  a  1  per  cent, 
solution  of  potassium  permanganate  solution ;  after 
decolorisation  an  additional  10  drops  are  added,  one  by 
one.  Normal  wine  vinegars  yield  a  slight  turbidity  in 
this  case,  while  those  containing  0-10  grm.  or  more  of 
citric  acid  per  litre  give  a  pronounced  turbidity. 

Oxalic  Acid. — The  following  method  is  recommended  by 
Calvet  *  : — Fifty  c.c.  of  the  vinegar  are  neutralised,  and 
the  oxalic  acid  precipitated  as  calcium  oxalate  by  means 
of  calcium  acetate.  The  precipitate  is  washed  and 
oxidised  with  a  standardised  sulphuric  acid  solution  of 
potassium  permanganate  ;  or  it  is  sulphated,  dried,  and 
weighed  as  calcium  sulphate.  The  weight  multiplied  by 
the  factor  18-55  gives  the  amount  of  oxalic  acid  per  litre 
of  vinegar. 

COLOURING  MATTERS. 

The  recommendation  of  the  Local  Government  Board, 
to  the  effect  that  the  only  colouring  matter  which  it 

*  Alcool  Mtthylique,  Vinaigres,  1912,  p.  136. 


METHODS    OF  EXAMINATION.  157 

should  be  permissible  to  add  to  vinegar  should  be  caramel 
is  almost  universally  accepted  in  this  country. 

Vinegar  brewed  from  malt  or  malt  and  cereals  is  of 
too  pale  a  colour  to  be  generally  acceptable,  except  in 
Scotland,  and  it  is,  therefore,  essential  to  add  some 
colouring  matter  to  meet  the  popular  taste.  Although 
aniline  dyestuffs  may  possibly  be  used  for  this  purpose, 
caramel  has  long  been  regarded  as  the  most  suitable 
colouring  matter  from  every  point  of  view. 

Measurement  of  Colour  Intensity. — Owing  to  the  great 
variations  in  the  tinctorial  power  of  different  varieties  of 
caramel,  it  is  not  easy  to  fix  upon  a  standard  substance 
upon  which  to  base  subsequent  measurements.  Even  if 
a  standard  solution  is  made  up  from  a  particular  sample 
of  caramel  and  kept  for  comparison  with  subsequent 
samples,  gradual  fading  takes  place,  especially  if  the 
bottle  is  exposed  to  the  light.  Some  slight  decomposi- 
tion and  deposition  of  the  pigment  is  also  inevitable  in 
the  course  of  time. 

An  iron  compound  which,  when  dissolved,  would  give 
the  required  shade  of  colour  might  possibly  be  used  for 
the  purpose,  but  this  would  involve  the  use  of  an  absol- 
utely pure  salt,  which  would  have  to  be  weighed  out 
and  dissolved  before  each  comparison,  since  it  would 
not  be  stable  in  solution. 

Iodine  solutions  of  standard  strength  were  adopted  by 
the  Berlin  Congress  of  1903  for  measuring  the  colour  of 
malt  products,  but  they  are  only  suitable  for  light-coloured 
worts,  since  the  tint  of  iodine  is  considerably  redder  than 
that  of  strong  malt  worts. 

To  obviate  this  drawback  Brand  and  Jais  *  suggested 

*  Ze.it.  ges.  Brauw.,  1906,  xxix.,  337. 


158     VINEGAK  :    ITS   MANUFACTURE   AND    EXAMINATION. 

the  use  of  aniline  dyestuffs  to  obtain  a  standard  corre- 
sponding in  intensity  of  shade  to  §  iodine,  and  equivalent 
in  colour  tone  to  the  colouring  matter  of  malt  or  caramel 
at  all  concentrations. 

This  system  has  the  same  drawbacks  as  the  use  of  an 
iron  salt,  especially  the  deterioration  of  the  tinctorial 
value  of  the  standard  solutions  on  keeping. 

Hence,  the  invention  of  Lovibond's  tintometer  has 
been  of  material  service  to  all  who  have  to  match  and 
keep  a  record  of  colours,  and  the  apparatus  is  now  ex- 
tensively used  in  many  industries. 

Lovibond's  Tintometer. — The  use  of  this  instrument 
is  based  upon  a  comparison  of  the  coloured  substance 
with  a  series  of  standard  coloured  glasses,  which  can  be 
blended  in  such  a  way  as  to  give  the  same  colour 
sensation. 

For  the  purposes  of  brewers  and  vinegar  makers  a 
special  series  of  these  glasses  approximating  to  the  colour 
of  solutions  of  malt  extract  or  caramel  is  provided,  the 
liquid  being  placed  in  a  glass  cell  1  inch  or  J  inch  in  width, 
while  the  numbered  glasses  are  placed  in  a  small  holder, 
and  viewed  simultaneously  through  the  instrument  in  a 
good  light. 

It  has  been  shown  by  Baker  and  Hulton  *  that  agree- 
ment between  the  results  obtained  by  different  observers 
depends  on  various  conditions,  such  as  the  relation  of 
the  instrument  to  the  source  of  light,  and  from  the  results 
of  their  experiments  they  make  the  following  recom- 
mendations : — (1)  The  tintometer  should  be  used  in  a 
horizontal  position  directed  to  a  north  window  covered 
with  white  tissue  paper  ;  (2)  it  should  not  be  more  than 

*  Journ.  Inst.  Brewing,  1907,  xiii.,  26. 


METHODS   OF   EXAMINATION.  159 

2  to  3  feet  from  the  window  ;  and  (3)  the  opal  screen 
of  the  instrument  should  be  discarded. 

In  the  writer's  experience  it  is  possible  to  match  the 
colours  of  most  vinegars  by  means  of  the  "  52  "  series 
of  glasses,  although  in  some  cases  a  glass  of  the  "  50  " 
series  may  be  required. 

When  examined  in  a  1-inch  cell  the  pale  vinegars  of 
commerce  range  from  about  5  to  10  in  the  "  52  "  series, 
medium- coloured  vinegars  from  15  to  20,  and  dark 
vinegars  from  30  to  40. 

In  the  case  of  the  darkest  products  it  is  advisable  to 

O 


Fig.  52. — Lovibond's  Tintometer. 

dilute  the  liquid  with  an  equal  volume  of  water,  since 
the  results  of  two  observers  will  agree  better  under  such 
conditions  than  when  a  very  dark  liquid  is  examined 
without  dilution. 

DETECTION  OF  CARAMEL. 

The  Fuller's  Earth  Test. — It  is  frequently  possible  to 
precipitate  the  whole  of  the  added  caramel  by  treating 
the  vinegar  with  a  little  fuller's  earth  that  has  been 


160     VINEGAR  :    ITS  MANUFACTURE  AND   EXAMINATION. 

proved  to  be  active  in  this  respect.  For  example,  wood 
vinegar  may  usually  be  completely  decolorised  in  this 
way. 

But  when  applied  to  vinegars  which  owe  part  of  their 
colour  to  products  formed  in  the  drying  of  the  malt  or 
grain  too  much  reliance  must  not  be  placed  upon  this 
test. 

Thus,  it  has  been  shown  by  Dubois  *  that  the  amount 
of  colour  removed  from  a  cider  vinegar  may  vary  from 
nothing  to  72  per  cent.,  and  that  the  proportion  will 
differ  with  different  kinds  of  earth.  Hence,  a  sample  of 
vinegar  which  gave  no  deposit  when  treated  with  one 
earth,  would  be  regarded  as  containing  added  caramel 
when  treated  with  another  earth.  Nor  are  the  results 
given  by  the  same  earth  uniform.  Thus,  in  Dubois' 
experiments,  an  earth  which  removed  no  colour  from  one 
pure  vinegar  removed  the  larger  proportion  from  another 
pure  sample. 

At  best,  the  test  must  be  regarded  as  a  preliminary  one. 
If  all  colour  is  removed,  caramel  is  undoubtedly  present, 
while  if  little  or  no  colour  is  removed  the  sample  may  be 
regarded  as  free  from  caramel.  But  in  the  case  of  most 
vinegars,  from  which  about  25  to  75  per  cent,  of  colour 
is  removed,  the  test  is  inconclusive. 

Lichthardt  -f  uses  a  method  of  precipitation  with 
tannin  as  a  test  for  caramel  in  vinegar,  flavouring  extracts, 
etc.  Five  c.c.  of  a  solution  of  1  grm.  of  gallotannic  acid 
and  0-75  grm.  of  sulphuric  acid  (sp.  gr.  1-84)  in  50  c.c. 
of  water  are  added  to  the  vinegar,  and  the  mixture  heated 
until  the  precipitate  that  first  forms  is  dissolved.  The 

*  J.  Amer.  Chem.  Soc.,  1907,  xxix.,  75. 
t*/.  Ind.  Eng.  Chem.,  1910,  ii.,  389. 


METHODS    OF   EXAMINATION.  161 

liquid  is  then  allowed  to  stand  for  12  hours,  and  in  the 
presence  of  caramel  a  light  or  dark  brown  deposit  will 
be  present. 

The  objection  to  this  test  is  that  albuminous  substances 
and  iron  compounds  also  react  with  tannin,  so  that  the 
formation  of  a  precipitate  is  not  a  conclusive  indication 
of  caramel. 

The  method  officially  used  in  France  for  wine  vinegar  is 
to  shake  50  to  100  c.c.  of  the  sample  with  50  c.c.  of 
ether,  to  allow  the  colourless  ethereal  layer  to  evaporate 
spontaneously,  and  to  test  the  residue  with  2  to  3  drops 
of  freshly  prepared  1  per  cent,  solution  of  resorcinol  in 
hydrochloric  acid.  In  the  presence  of  caramel  a  rose 
coloration  will  be  obtained  (Fiehe's  reaction). 

If  the  ethereal  layer  is  coloured,  it  should  be  washed 
with  water  rendered  slightly  ammoniacal,  and  evaporated. 
Or,  if  necessary,  the  residue  may  be  taken  up  with  25  c.c. 
of  water,  and  the  solution  boiled  with  a  little  egg-albumin 
(white  of  egg),  the  colouring  matter  being  removed  by 
the  coagulated  albumin. 

It  has  been  shown  by  Anderson  *  that  pure  cider 
vinegars  contain  furfural,  and  that  Fiehe's  reaction  is, 
therefore,  not  necessarily  an  indication  of  the  presence 
of  caramel  in  such  vinegars. 

Amthor  j-  bases  a  method  of  detecting  caramel  upon 
its  precipitation  with  paraldehyde.  Ten  c.c.  of  the 
vinegar  are  mixed  with  30  c.c.  of  paraldehyde  and  suffi- 
cient absolute  alcohol  to  obtain  a  clear  solution,  and  the 
mixture  left  for  24  hours  in  a  closed  flask. 

The  precipitate  is  washed  with  absolute  alcohol  and 
dissolved  in  water,  and  the  solution  evaporated  to  1  c.c., 

*  Ibid.,  1914,  vi.,  214,  t Zeit-  anal-  Chem.,  xxiv.,  30. 

11 


162     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

and  heated  for  30  minutes  at  100°  C.  with  a  small  quantity 
of  an  acetic  acid  solution  of  phenyl-hydrazine.  If  the 
precipitate  consisted  of  caramel  an  amorphous  compound 
(probably  composed  of  phenyl-hydrazones  and  osazones) 
is  obtained. 

Various  colorimetric  methods  of  estimating  caramel 
have  been  suggested  (e.g.)  by  Smith,  Amer.  J.  Pharm., 
1911,  Ixxxiii.,  411),  but  since  commercial  samples  vary 
widely  in  their  chemical  composition,  according  to  the 
different  methods  of  manufacture  in  use,  none  of  these 
can  lay  claim  to  much  accuracy. 

In  practice  caramel  is  bought  upon  the  basis  of  its 
colouring  capacity  without  reference  to  the  chemical 
compounds  to  which  its  colour  is  due. 

The  method  recommended  by  a  Committee  of  the 
Institute  of  Brewing  *  is  essentially  the  same  as  that 
used  by  the  present  writer  for  many  years  : — Ten  grms. 
of  the  sample  are  dissolved  in  100  c.c.  of  water  at  15-5°  C., 
and  the  solution  diluted  to  a  litre,  and  compared  in  a  1-inch 
cell  with  glass  of  "52  "  series  in  Lovibond's  tintometer. 

Coloured  Wine  Vinegars. — The  coloration  of  wine 
vinegars  with  cochineal  or  archil  is  allowed  by  the  French 
law.  The  official  methods  used  in  France  in  the  detec- 
tion of  these  colouring  matters  are  as  follows  : — 

Cochineal. — Twenty-five  c.c.  of  the  vinegar  are  shaken 
for  five  minutes  with  20  c.c.  of  ether,  and  the  ethereal 
extract  treated  with  a  few  drops  of  ammonia  solution. 
In  the  presence  of  cochineal  a  carmine  red  coloration  is 
obtained. 

As  a  confirmatory  test  4  c.c.  of  the  vinegar  are  neutral- 
ised and  treated  with  1  c.c.  of  a  1  per  cent,  solution  of 

*  Jovrn.  Inst.  Brewing,  1910,  xvi.,  529. 


METHODS   OF   EXAMINATION.  163 

ammonium  alum  followed  by  1  c.c.  of  a  10  per  cent,  sodium 
carbonate  solution.  The  resulting  lake  will  be  bluish- 
violet,  and  the  filtrate  violet,  if  the  colouring  matter  was 
cochineal. 

Archil. — Twenty-five  c.c.  of  the  vinegar  are  made 
slightly  alkaline  with  ammonia,  and  shaken  with  10  c.c. 
of  amyl  alcohol,  a  violet  coloration  being  obtained  in  the 
presence  of  archil.  The  extract  is  evaporated,  and  the 
residue  treated  with  one  drop  of  sulphuric  acid,  which 
gives  a  coloration  changing  to  bluish-violet  on  addition 
of  ammonia. 

METALLIC  IMPURITIES. 

Vinegar  is  very  liable  to  become  contaminated  with 
metallic  impurities,  such  as  iron  and  copper,  derived  from 
hoops  upon  the  vats,  brass  taps,  and  the  like,  with  which 
it  may  come  into  contact. 

Iron. — The  presence  of  traces  of  iron  is  mainly  of 
importance  from  the  fact  that  when  the  vinegar  comes 
in  contact  with  the  wood  in  a  new  barrel  a  black  iron 
tannate  will  be  formed,  which  will  cause  the  vinegar  to 
become  dark  and  unsaleable. 

The  presence  of  iron  may  be  detected  by  adding 
potassium  ferrocyanide  directly  to  the  vinegar,  and  it 
may  be  estimated  colorimetrically  in  the  ash  by  means 
of  the  same  reaction. 

Copper,  Lead,  and  Tin. — For  the  detection  of  these 
metals  100  c.c.  of  the  vinegar  are  boiled  with  10  c.c.  of 
hydrochloric  acid,  and  potassium  chlorate  introduced  in 
small  quantities  at  a  time  until  a  colourless  solution  is 
obtained.  This  is  treated  with  sodium  acetate  to  remove 


164    VINEGAR  :    ITS   MANUFACTURE    AND    EXAMINATION. 

the  hydrochloric  acid  and  a  current  of  hydrogen  sul- 
phides passed  through  the  liquid. 

Copper  may  be  estimated  electrolytically  in  the  vinegar 
itself.  A  few  drops  of  nitric  acid  are  added  to  100  c.c. 
of  the  sample,  which  is  then  electrolysed  for  30  minutes 
with  a  current  of  2  vols.  and  1  amp.  per  square  decimetre. 
The  copper  is  deposited  on  the  electrodes  in  the  usual 
way. 

In  testing  for  lead  the  ash  from  the  vinegar  is  moistened 
with  acetic  acid  and  treated  with  an  excess  of  dilute 
ammonia  solution,  and  the  liquid  boiled  and  filtered. 
This  treatment  is  repeated  several  times  to  effect  complete 
extraction,  and  the  filtrates  are  united,  and  made  up  to 
a  definite  volume.  In  the  presence  of  copper  a  brown 
coloration  will  be  obtained  on  the  addition  of  potassium 
ferrocyanide  to  a  small  part  of  the  liquid. 

If  no  copper  is  found,  the  solution  is  rendered  acid 
with  hydrochloric  acid,  and  tested  for  lead  with  a  solution 
of  hydrogen  sulphide. 

When  copper  is  present  an  addition  of  a  small  quantity 
of  potassium  cyanide  should  be  made  before  applying 
the  test  for  lead,  The  ferrocyanide  test  for  copper  and 
the  hydrogen  sulphide  test  for  lead  may  be  used  for  the 
colorimetric  estimation  of  traces  of  those  metals,  the  tint 
produced  being  matched  with  standard  solutions  of  lead 
and  copper  salts. 

Tin. — The  ash  of  the  vinegar  is  fused  with  sodium 
hydroxide,  and  the  mass  extracted  with  boiling  water 
containing  a  little  hydrochloric  acid.  The  filtered  extract 
is  tested  with  hydrogen  sulphide,  which  in  the  presence 
of  tin  gives  a  yellow  coloration  or  precipitate. 

Arsenic. — The  discovery,  in  1900,  that  several  cases  of 


METHODS   OF   EXAMINATION.  165 

peripheral  neuritis  had  been  caused  by  drinking 
beer  containing  arsenic  drew  general  attention  to  the 
possibility  of  the  occurrence  of  dangerous  amounts  of 
arsenic  in  other  food  products. 

The  Royal  Commission  appointed  in  1901  to  investigate 
the  subject  found  that  the  glucose  used  in  the  preparation 
of  these  arsenical  beers  contained  quantities  of  arsenic 
ranging  from  0-015  to  0-131  per  cent.,  and  that  in  the 
case  of  one  sample  of  beer  the  amount  of  arsenic  reached 
3  grains  per  gallon. 

The  original  source  of  this  arsenic  was  discovered  in 
the  sulphuric  acid  used  in  the  preparation  of  the  brewing 
sugar,  some  of  the  samples  of  acid  containing  as  much 
as  2-5  per  cent,  of  arsenic  (as  arsenious  acid). 

Arsenic  was  also  detected  in  other  beers  brewed  from 
malt,  the  poison  being  ultimately  traced  to  the  fuel  used 
for  the  kilns. 

Since  vinegars  are  brewed  upon  similar  lines  to  beer,  it 
is  not  surprising  that  traces  of  arsenic  were  found  in  many 
samples,  and  that  serious,  if  not  dangerous,  quantities 
were  present  in  vinegars  made  by  the  conversion  process, 
where  impure  sulphuric  acid  had  been  employed. 
.  Another  possible  source  of  arsenic  in  vinegar  is  the 
caramel,  which  is  almost  universally  employed  as  a 
colouring  material.  This  is  often  prepared  from  glucose, 
and  the  use  of  impure  acid  in  the  hydrolysis  of  the  starch 
has  been  known  to  cause  arsenic  to  be  present  in  the 
caramel. 

After  the  publication  of  the  report  of  the  Royal  Com- 
mission in  1903  precautions  were  taken  by  the  maltsters 
and  the  manufacturers  of  brewing  sugars  to  prevent 
recurrence  of  the  trouble,  and,  as  a  rule,  the  malt  now 


166     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

upon  the  market  seldom  contains  over  -^iF  grain  of  arsenic 
per  pound. 

In  1901  a  Conjoint  Committee  of  the  Society  of  Chemical 
Industry  and  of  the  Society  of  Public  Analysts  was 
appointed  to  examine  and  report  upon  the  various  methods 
of  detecting  and  estimating  arsenic,  and  in  the  following 
year  issued  the  subjoined  report,*  which,  if  exactly  fol- 
lowed, will  give  accurate  results  under  all  conditions  : — f 

"  MATERIALS  REQUIRED— Hydrochloric  Acid.— The  purest  hydro- 
chloric acid  obtainable  is  very  rarely  free  from  arsenic.  To  the  '  pure  ' 
acid,  as  purchase^  for  analysis,  diluted  with  distilled  water  to  a  specific 
gravity  of  1-10,  sufficient  bromine  is  added  to  colour  it  strongly  yellow 
(about  5  c.c.  per  litre),  sulphurous  acid,  either  gaseous  or  in  aqueous  solution, 
is  then  added  in  excess,  and  the  mixture  is  allowed  to  stand  for  at  least 
twelve  hours,  or  hydrobromic  and  sulphurous  acid  may  be  used  The 
acid  is  then  boiled  till  about  one-fifth  has  evaporated,  and  the  residue 
can  either  be  used  directly  or  may  be  distilled,  the  whole  of  the  arsenic 
having  volatilised  with  the  first  portion. 

"  Sulphuric  Acid. — This  is  more  frequently  obtainable  arsenic-free  than 
hydrochloric  acid.  If  not  procurable,  to  about  half  a  litre  of  sulphuric 
acid  '  pure  for  analysis/  a  few  grammes  of  sodium  chloride  are  added,  and 
the  mixture  distilled  from  a  non-tubulated  glass  retort,  the  first  portion  of 
about  50  c.c.  being  rejected.  For  the  purpose  of  the  test  to  be  described, 
one  volume  of  the  distilled  acid  is  diluted  with  four  volumes  of  water. 

"  Nitric  acid  can,  as  a  rule,  be  obtained  free  from  arsenic  without  much 
difficulty ;  the  pure  redistilled  acid  should  be  used.  This  should  be  tested 
by  evaporating  20  c.c.  in  a  porcelain  dish,  which  should  then  be  washed 
out  with  dilute  acid,  and  tested  as  described  in  this  report. 

"  The  purified  acids  should  be  prepared  as  required,  and  should  not  be 
stored  for  any  length  of  time.  If  this  is  unavoidable,  however,  Jena  flasks 
are  to  be  preferred,  since  most  bottle  glass  is  liable  to  communicate  traces 
of  arsenic. 

"  Zinc. — Arsenic-free  zinc  is  obtainable  from  chemical  dealers.  It  should 
be  regranulated  by  melting  it  and  pouring  it  from  some  height  into  cold 
water. 

*  The  report  is  condensed  here  ;  the  directions  for  testing  beer  are  also 
appk'cable  to  vinegar.  *  f  Analyst,  1902,  xxvii.,  48. 


METHODS    OF   EXAMINATION. 


167 


"  Lime. — Caustic  lime,  even  when  made  from  white  marble,  is  not  always 
free  from  arsenic.  A  selection  must,  therefore,  be  made  from  various 
samples.  If  pure  lime  is  not  obtainable,  magnesia  may  equally  well  be 
used,  and  can  be  more  readily  obtained  of  sufficient  purity. 

"  Calcium  Chloride. — This  salt  often  contains  arsenic,  and  before  being 
used  as  a  drying  agent  must  be  freed  from  the  volatilisable  part  of  the 
impurity  by  moistening  it  with  strong  hydrochloric  acid,  fusing  and  re- 
granulating. 

"  Apparatus. — A  bottle  or  flask  holding  about  200  c.c.  (for  frothing 
materials  preferably  wider  at  top  than  bottom)  is  fitted  with  a  double- 


r\ 


Fig.  53. — Arsenic  Apparatus. 

bored  cork,  india-rubber  stopper,  or  with  a  ground-in  glass  connection, 
carrying  a  topped  funnel  (holding  about  50  c.c.),  and  an  exit  tube.  The 
latter  is  connected  with  a  drying  tube  containing,  first,  a  roll  of  blotting 
paper  soaked  in  lead  acetate  solution,  and  dried,  or  a  layer  of  cotton  wool 
prepared  in  a  similar  way,  then  a  wad  of  cotton  wool,  then  a  layer  of  granu- 
lated calcium  chloride,  and  finally  a  thick  wad  of  cotton  wool.  To  this 
tube  is  fitted  a  hard-glass  tube  drawn  out  as  shown  in  the  figure,  and  of 
such  external  diameter  that  at  the  place  where  the  arsenic  mirror  is  to  be 
expected  the  tube  just  passes  through  a  No.  13  Birmingham  wire  gauge 
(corresponding  with  0-092  inch).  The  exact  size  is  not  material,  but  all 


168    VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

tubes  used  for  standards  and  tests  should  be  as  nearly  as  practicable  of  the 
same  diameter.  A  good  Bunsen  flame  is  used  to  heat  the  hard-glass  tube 
close  to  the  constriction.  About  1  inch  of  tube,  including  the  shoulder, 
ought  to  be  red  hot.  A  piece  of  moderately  fine  copper  gauze  (about  1  inch 
square)  wrapped  round  the  portion  of  tube  to  be  heated  assists  in  insuring 
equal  distribution  of  heat.  A  suitable  form  of  apparatus  is  shown  in  the 
accompanying  figure. 

"  About  20  grammes  of  zinc  are  placed  in  the  bottle  and  washed  with 
water  to  clean  the  surface,  as  particles  of  dust  may  contain  arsenic  ;  all 
parts  of  the  apparatus  are  connected,  and  a  sufficient  quantity  of  acid 
(prepared  as  previously  described)  allowed  to  flow  from  the  funnel,  so  as 
to  cause  a  fairly  brisk  evolution  of  hydrogen.  When  the  hydrogen  flame, 
which  during  the  heating  of  the  tube  should  be  kept  at  as  uniform  a  height 
as  possible  (about  a  quarter  of  an  inch),  burns  wi^h  a  round,  not  pointed, 
tip,  all  air  has  been  removed  from  the  apparatus.  The  Bunsen  burner 
should  then  be  placed  under  the  hard-glass  tube  as  described,  and  more 
acid  (10  to  20  c.c.  are  generally  enough)  run  in  as  required.  With  good 
materials  no  trace  of  a  mirror  is  obtained  within  half-an-hour. 

"  Great  care  must  be  taken  that  when  additions  of  acid  are  made  to  the 
zinc  no  bubble  of  air  is  introduced,  since  in  presence  of  air  the  arsenic  mirror 
may  become  black  and  unevenly  distributed,  whilst  it  is  brown  when  the 
experiment  has  been  properly  conducted. 

"  Should  the  blank  experiment  not  be  satisfactory,  it  must  be  ascertained 
by  changing  the  materials  methodically  whether  the  fault  lies  with  the 
acid,  zinc,  other  materials,  or  with  the  apparatus. 

"  Preparation  Of  Standard  Mirrors. — When  a  satisfactory  blank  experi- 
ment has  been  obtained  a  series  of  standard  mirrors  must  be  prepared 
under  the  following  conditions : — A  hydrochloric  acid  solution  of  arsenious 
oxide  containing  in  each  c.c.  0-001  milligramme  As406  is  prepared  by  diluting 
a  stronger  solution  with  distilled  water.  Two  c.c.  of  this  solution  (equal 
to  0-002  milligramme  of  arsenious  oxide)  are  introduced  into  the  apparatus, 
a  new  tube  having  been  joined  to  the  drying  tube.  If  the  zinc  is  sensitive 
a  distinct  brown  mirror  is  obtained  after  twenty  minutes.  It  is  important 
to  note  that  some  '  pure '  zinc  is  from  a  cause  at  present  unknown  *  not 
sufficiently  sensitive — that  is  to  say,  the  addition  of  minute  quantities  of 
arsenic  produces  no  mirrors.  The  portion  of  tube  containing  the  mirror 
should  be  sealed  off  while  still  filled  with  hydrogen ;  in  contact  with  air 
the  mirrors  gradually  fade.  Mirrors  are  now  similarly  made  with  0-004, 
0-006,  0-008,  and  0-01  milligramme  of  arsenious  oxide.  With  a  little 

*  Chapman  and  Law,  Analyst,  1906,  3. 


METHODS   OF   EXAMINATION.  169 

patience  it  is  easy  to  obtain  the  deposits  of  arsenic  neatly  and  equally 
distributed.  The  standard  mirrors,  properly  marked,  are  mounted  on  a 
white  card  or  porcelain  slip.  It  is  to  be  understood  that  the  first  stage  of 
every  test  must  be  a  blank  of  at  least  twenty  minutes. 

"  Organic  materials,  such  as  yeast,  beer,  etc.,  cannot  be  tested  when 
sulphuric  acid  is  used,  without  destruction  of  organic  matter,  whilst  as  a 
rule  they  can  be  directly  tested  with  hydrochloric  acid. 

"Procedure  without  Destruction  of  Organic  Matter.— The  apparatus  is 
started,  and  a  blank  experiment  allowed  to  go  on  for  20  minutes.  If 
no  trace  of  deposit  is  obtained  10  c.c.  of  the  liquid  to  be  tested  and  about 
10  c.c.  of  hydrochloric  acid  are  put  into  the  funnel  and  slowly  introduced 
into  the  bottle  without  air-bubbles.  Some  materials  (beers,  for  example) 
are  apt  to  froth  ;  hence  the  necessity  for  slow  introduction.  If  after  about 
10  minutes  no  mirror  appears,  another  10  c.c.  of  the  liquid,  with  10  c.c. 
of  hydrochloric  acid,  are  added,  and  the  experiment  continued  for  15  to 
20  minutes,  acid  being  added  from  time  to  time  as  may  appear 
necessary. 

"  Malt. — Fifty  grammes  of  the  malt  are  placed  in  a  300  c.c.  separator 
funnel  with  a  stopcock  ;  50  c.c.  of  hydrochloric  acid,  prepared  as  described, 
and  50  c.c.  of  water  are  warmed  to  about  50°  C.  and  poured  on  the  malt. 
The  whole  is  then  allowed  to  digest  for  15  to  20  minutes  with  frequent 
agitation,  and  the  acid  then  allowed  to  run  off  by  the  stopcock.  About 
60  c.c.  of  the  acid  liquor  is  thus  obtained,  of  which  20  c.c.  contains  the 
arsenic  from  10  grammes  of  malt. 

"  Sugar  and  other  brewing  materials  are  dissolved  in  water,  10  c.c.  of 
acid  added,  and  the  solution  tested  direct,  operating  upon  10  to  20  grammes 
of  material. 

"  Destruction  of  Organic  Matter — (a)  Acid  Method. — Ten  grammes  of  the 
substance  are  placed  in  a  3£-inch  porcelain  crucible,  and  covered  with  pure 
distilled  nitric  acid  (about  10  to  15  c.c.).  The  whole  is  then  heated  on  a 
sand  bath  until  the  evolution  of  brown  fumes  ceases.  Three  c.c.  of  con- 
centrated arsenic-free  sulphuric  acid  are  then  added,  and  the  heating 
continued  until  the  mass  just  begins  to  char,  when  a  further  quantity  of 
5  c.c.  of  nitric  acid  is  added.  The  heating  is  now  continued  until  all  acid 
is  expelled,  leaving  in  the  crucible  a  black,  nearly  dry,  charred  mass.  The 
crucible  is  about  half  filled  with  water,  and  a  few  c.c.  of  hydrochloric  acid 
or  dilute  sulphuric  acid  run  in  (according  as  the  one  or  the  other  is  to  be 
used  in  the  Marsh  apparatus),  the  whole  being  allowed  to  extract  for  about 
half -an-h our  on  a  water-bath.  It  is  then  filtered  into  a  porcelain  basin, 
the  charred  mass  washed  with  hot  water,  and  the  filtrate  concentrated 
down  to  about  30  c.c.,  which  is  allowed  to  cool,  and  is  then  ready  for  the 


170      VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

test.  It  is  essential  that  the  mass  should  be  thoroughly  charred,  and  that 
the  solution  when  filtered  should  be  colourless. 

"  In  the  case  of  beer,  10  to  20  c.c.  are  evaporated  to  dryness,  and  the 
residue  oxidised  as  above  stated. 

"  (6)  Basic  Method. — The  materials  are  mixed  with  pure  lime  or  magnesia 
(1  gramme  for  20  c.c.  of  beer),  dried,  and  incinerated.  For  sugars  or  other 
solid  materials  about  half  their  weight  of  base  is  employed.  The  ash  is 
dissolved  in  hydrochloric  acid,  and  the  solution  tested. 

"  The  proof  that  the  mirrors  are  arsenical  is  obtained  as  follows : — The 
narrow  portion  of  the  tube  containing  the  mirror  (which  should  not  be 
denser  than  that  produced  by  0-01  milligramme  of  arsenious  oxide)  is  cut 
off,  the  hydrogen  replaced  by  air,  and  the  ends  sealed  up.  The  tube,  held 
in  the  tongs,  is  then  heated  by  drawing  it  repeatedly  through  the  flame 
of  a  Bunsen  lamp  until  the  mirror  has  disappeared.  On  cooling,  minute 
crystals  of  arsenious  oxide  deposit,  the  sparkling  of  which  can  be  seen 
by  the  naked  eye  if  the  tube  be  held  before  a  luminous  flame,  and  which 
can  be  readily  identified  under  the  microscope  by  their  crystalline  form. 

"  This  test,  as  recommended,  is  one  of  such  extreme  delicacy  that  with 
quantities  of  20  grammes  (or  20  c.c. )  it  will  give  an  indication  of  the  presence 
of  0-000015  per  cent,  (or  1  part  in  7,000,000)  of  arsenious  oxide." 


171 


CHAPTER  X. 
CHARACTERISTICS   OF  DIFFERENT  VINEGARS. 

Interpretation  of  Results — CHEMICAL  STANDARDS — Acetic  Strength — Total 
Solids — 'k  Original  Solids  " — Nitrogen  and  Phosphoric  Acid — Optical 
Standard — MALT  VINEGARS — The  Malt  Vinegar  Question — Composi- 
tion of  Malt  Vinegars — Cider  Vinegar — Wine  Vinegar — Whey  Vinegar 
— Fruit  and  Herb  Vinegars — Date  Vinegar — Spirit  Vinegars — Essig- 
sprit — Wood  Vinegar — Composition  of  Artificial  Vinegars. 

THE  interpretation  of  the  results  of  an  analysis  is  by  no 
means  an  easy  problem  in  the  case  of  certain  kinds  of 
vinegar.  Although  analysis  will  show  that  a  vinegar 
must  be  a  wood  vinegar  or  spirit  vinegar  or  distilled 
vinegar,  it  is  not  possible  to  state  with  certainty  the 
origin  of  some  grain  vinegars.  For  example,  a  safe 
deduction  may  be  drawn  from  the  deficiency  of  certain 
constituents  that  a  vinegar  has  not  been  manufactured 
in  a  normal  way  from  malted  or  unmalted  barely,  but  it 
may  not  be  justifiable  to  assert  that  it  has  not  been  derived 
from  a  mixture  of  malted  barley  and  unmalted  cereals- 
In  the  absence  of  legal  standards  for  the  composition  of 
the  different  kinds  of  vinegar,  the  analyst  can  only  draw 
probable  conclusions  from  a  comparison  of  his  figures 
with  the  average  results  of  products  presumably  brewed 
in  the  same  way.  The  danger  of  placing  too  much  reliance 
upon  such  comparisons  was  shown  in  a  recent  prosecution 
for  the  sale  of  a  vinegar  which  the  analyst  asserted  was 
not  wholly  derived  from  malt.  The  Stipendiary,  in  dis- 


172    VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

missing  the  case,  remarked,  "  This  is  not  an  analysis,  but 
a  guess/' 

CHEMICAL  STANDARDS  FOR  VINEGAR. 

Acetic  Strength. — The  standard  suggested  by  the 
Local  Government  Board  in  their  definitions  of  vinegar 
and  artificial  vinegar,  of  a  minimum  of  4  per  cent,  of  acetic 
acid,  has  already  been  mentioned. 

There  have  been  numerous  prosecutions  and  con- 
victions for  the  sale  of  vinegar  containing  less  than 
4  per  cent,  of  acetic  acid,  and  the  bulk  of  the  vinegar 
sold  throughout  the  country  is  now  in  excess  of  the 
4  per  cent,  standard. 

There  is,  however,  no  general  agreement  on  the  point, 
and  even  during  the  current  year  conflicting  decisions 
have  been  given  by  magistrates. 

Legal  standards  for  the  strength  of  vinegar  are  found 
in  the  food  regulations  of  some  of  the  Colonies  and  in 
foreign  countries.  For  example,  in  Australia  and  in  the 
United  States  the  same  minimum  standard  for  strength 
(4  per  cent.)  has  been  adopted. 

Standard  for  Total  Solids. — Early  in  1907  the  London 
and  Country  Vinegar  Brewers'  Association  passed  a 
resolution,  to  the  effect  that  the  conditions  specified  in 
the  Admiralty  contract  were  a  correct  definition  of  what 
No.  20  Vinegar  should  be  : — 

"  The  vinegar  of  No.  20  trade  denomination,  which 
contains  5-17  per  cent,  or  22-6  grains  by  weight  of  real 
acetic  acid  (C2H402)  per  fluid  ounce.  It  shall  have  a 
specific  gravity  at  60°  F.  of  1-017  to  1-021,  and  be  whoUy 
the  product  of  alcoholic,  acetous  fermentation  in  the 


CHARACTERISTICS   OF   DIFFERENT   VINEGARS.          173 

vinegar  itself,  and  that  they  were  prepared  to  support 
local  authorities  in  establishing  such  a  standard,  and 
that  higher  and  lower  strengths  of  vinegar  be  based  on 
this  definition/'  * 

No  attempt  was  made  by  the  Local  Government  Board 
to  give  force  to  this  proposed  standard  of  a  minimum  of 
total  solid  matters.  In  fact,  one  firm  declined  to  support 
the  resolution  upon  the  ground  that  to  leave  a  large 
proportion  of  unfermented  substances  in  the  wash  would 
lead  to  bad  and  uneconomical  brewing. 

Moreover,  a  well-attenuated  wash  from  an  all-malt 
brew  might  have  a  much  lower  specific  gravity  than  a 
wash  prepared  from  glucose  containing  a  large  amount 
of  unfermentable  substances.  At  best,  such  a  standard 
would  have  had  the  effect  of  making  a  sharper  differenti- 
ation between  brewed  and  artificial  vinegars,  which  are 
usually  sold  at  a  cost  that  would  not  permit  of  the  addition 
of  suitable  substances  to  raise  the  specific  gravity. 

Calculation  of  "Original  Solids."  —  An  empirical  but 
convenient  method  of  comparing  the  analytical  results 
of  the  examination  of  vinegars  of  different  acetic  strength 
was  devised  by  Hehner.f 

It  is  based  upon  a  calculation  of  the  percentage  of  the 
different  constituents  upon  100  parts  of  the  solid  matter 
estimated  to  have  been  present  in  the  original  wort. 
Since  180  parts  of  dextrose  can  be  theoretically  converted 
into  120  parts  of  acetic  acid,  the  "  original  solids  "  are 
found  by  multiplying  the  percentage  of  acetic  acid  by 
the  factor  1-5  and  adding  the  product  to  the  amount  of 
total  solids  still  remaining  in  the  vinegar. 

For  example,  in  the  case  of  a  vinegar  containing  4-92 

*  Dr.  Hamill's  Report,  1908,  p.  16.  t  Analyst,  1891,  xvi.,  92. 


174     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

per  cent,  of  acetic  acid  and  2-27  per  cent,  of  total  solids, 
the  "original  solids"  would  be  (4-92  x  1-5)  +  2-27  = 
9-65  per  cent. 

It  was  pointed  out  by  Allen  and  Moore  *  that  in  practice 
the  yield  of  acetic  acid  seldom  exceeds  two-thirds  of 
the  theoretical  amount,  so  that  a  more  correct  estimation 
of  the  original  solids  in  the  wort  would  be  made  by  multi- 
plying the  amount  of  acetic  acid  by  ^  (  =  2-25)  and 
adding  this  result  to  the  total  solids  found  in  the  vine- 
gar. Applying  this  method  of  calculation  to  the  example 
given  above,  the  "  original  solids  "  would  be  13-44  per  cent. 

As  it  is  impossible,  owing  to  the  variety  of  materials 
used  for  brewing,  and  the  variations  in  the  loss  on  aceti- 
fication,  to  arrive  at  a  true  figure  for  the  "  original  solids," 
there  seems  to  be  no  advantage  in  substituting  the  value 
as  calculated  by  Allen  and  Moore  for  the  theoretical 
value  suggested  by  Hehner. 

Nitrogen  and  Phosphoric  Acid. — The  proportion  of  one 
or  both  of  these  constituents  calculated  upon  the  "  original 
solids  "  of  the  vinegar  is  usually  taken  into  consideration 
in  giving  an  opinion  upon  the  origin  of  a  vinegar. 

In  the  case  of  a  vinegar  brewed  from  an  average  barley 
malt,  the  amounts  of  nitrogen  and  phosphoric  acids  in 
the  "  original  solids  "  will  usually  exceed  0-5  per  cent., 
and  the  two  quantities  of  the  two  constituents  will  be 
approximately  equal.  This  is,  of  course,  assuming  that 
no  process  has  been  used  whereby  the  proportion  of 
either  is  reduced. 

Barley  malts  vary  widely  in  their  composition,  as  is 
shown  by  the  following  analyses  by  Salamon  t  of  sixteen 
samples  of  dried  malt : — 

*  Ibid.,  1893,  xviii.,  245.  1 7.  Soc.  Chem.  Ind.f  1885. 


CHARACTERISTICS   OF   DIFFERENT   VINEGARS. 


175 


Mineral 
Ash. 

Total  Nitrogen 
from 
.Nitrogenous 
Substances. 

Total  Nitrogen 
from  Soluble 
Nitrogenous 
Substances. 

Phosphoric 
Anhydride, 
P205. 

Highest, 
Lowest,  . 

Per  cent. 
3-41 
2-09 

Per  cent. 
1-70 
1-27 

Per  cent. 
1-193 
0-662 

Per  cent. 
1-10 
0-635 

It  will  thus  be  seen  that  malt  made  from  badly-germi- 
nated barley  will  contain  much  less  soluble  nitrogen 
than  that  from  well-grown  barley  that  has  germinated 
satisfactorily. 

At  the  same  time,  it  is  hardly  probable  that  vinegar 
made  from  a  malt  containing  only  relatively  small 
amounts  of  soluble  nitrogen  and  phosphoric  acid,  such 
as  the  lowest  figures  recorded  above,  would  contain  less 
than  the  0-5  per  cent,  of  each  constituent  calculated 
upon  the  original  "  solids/' 

But  the  conditions  are  totally  different  when  a  mixture 
of  malted  barley  or  other  malt  with  raw  grain  is  used, 
as  is  obvious  from  a  glance  at  the  following  analyses 
made  by  Gilbert : — * 


Barley. 

Rye. 

Maize. 

Oats. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

Moisture,    . 

12-0 

14-3 

11-5 

14-2 

Starch, 

52-7 

54-9 

64-8 

56-1 

Gums  and  sugars, 

4-2 

11-3 

2-9 

5-7 

Albuminoids  (soluble 

and  insoluble), 

13-2 

8-8 

8-9 

16-0 

Cellulose,    . 

11-5 

6-4 

14-9 

1-0 

Fat,  .         .         .  .:"•. 

2-6 

2-0 

4-7 

4-6 

Ash,  .         .      -  . 

2-8 

1-8 

1-6 

2-2 

Total,    .     '    ._ 

99-0 

99-5 

99-3 

99-8 

*  Quoted  by  Nettleton,  The  Manufacture  of  Spirit,  p.  392. 


176    VINEGAR:  ITS  MANUFACTURE  AND  EXAMINATION. 

Again,  according  to  von  Bibra,*  the  ash  of  rye  ranges 
from  1-97  to  2-05,  and  the  proportion  of  phosphoric  acid 
therein  from  42-38  to  50-35. 

Hence,  vinegars  brewed  from  mixtures  of  a  malted 
grain  with  any  of  these  raw  grains  would  show  enormous 
variations  in  the  proportions  of  nitrogen  and  phosphoric 
acid.  If  rye  were  used  the  values  for  both  the  con- 
stituents would  be  very  much  lower  than  if  barley 
were  the  grain,  while  if  rice  were  the  cereal  employed 
the  percentages  would  be  still  less,  and  would  fall  far 
below  those  of  a  vinegar  brewed  from  an  average  malted 
barley  or  a  mixture  of  malt  and  barley. 

For  these  reasons  it  is  obvious  that  even  if  the  defini- 
tion of  malt  vinegar  as  a  cereal  product,  the  sacchari- 
fication  of  which  has  been  initiated  by  the  diastase  of 
malt,  were  generally  accepted,  the  difficulty  of  distin- 
guishing analytically  between  the  different  classes  of 
cereal  vinegars  would  remain. 

If  prepared  cereals  are  employed,  the  results  will  differ 
from  those  obtained  with  ordinary  raw  grain,  as  is  shown 
by  the  following  analyses  of  prepared  grain,  which  have 
often  been  used  in  the  manufacture  of  vinegar.  These 
results  are  quoted  by  Nettleton.f 

The  effect  of  the  torrefying  process  on  the  barley  is 
to  reduce  the  oil  and  water,  and  to  increase  the  propor- 
tion of  starch,  while  leaving  the  amounts  of  mineral 
constituents  and  nitrogenous  substances  practically  the 
same. 

In  the  case  of  the  flaked  preparations  similar  changes 
take  place,  while  the  amounts  of  ash,  nitrogenous  sub- 

*  Odrungstechnische  Untersuchungs-metJioden  (Bauer),  p.  143. 
t  The  Manufacture  of  Spirit,  p.  394. 


CHARACTERISTICS   OF   DIFFERENT  VINEGARS. 


177 


stances,  and  phosphoric  acid  are  but  little  affected,  after 
making  allowance  for  the  different  proportions  of  water 
in  the  cereal  before  and  after  treatment. 


Torrefied  or 
Popped  Barley. 

Flaked  Maize. 

Flaked  Maize 
"Cerealine." 

Per  cent. 

Per  cent. 

Per  cent. 

Moisture,  . 

3-9 

7-75 

13-33 

Oil,  .... 

1-97 

1-32 

*a-*-*{£SX 

0-88 
12-62 

0-65 
7-75 

I       8-54 

Starch  and  sugars, 

71-65 

67-36 

75-50 

I 

15-25 

I' 

Woody  fibre  and  cellulose, 

6-03     J 

(including 

0-80 

1 

the  oil) 

Mineral  ash, 

2-95 

1-24 

Chapman  *  has  shown  that  the  proportion  of  phosphoric 
acid  in  a  vinegar  depends,  not  only  upon  the  composition 
of  the  cereal,  but  also  upon  the  nature  of  the  mineral 
salts  in  the  brewing  water. 

This  was  illustrated  by  the  following  experiments,  in 
which  two  different  malts  were  mashed  with  waters  of 
different  degrees  of  hardness,  and  the  proportions  of 
phosphoric  acid  in  the  filtrates  were  determined  : — 

MALT,   A.  Phosphoric  Aeid  (P206)- 

Grains  per  Gallon. 

Distilled  water,  .          .          .          .46-56 

Water  containing  20  grains  total  solids,     42-44 
Very  hard  water,        .          .          .          .30-44 

MALT,  B. 

Distilled  water,  ....     44-77 

Water  containing  20  grains  total  solids ,      37-61 
Very  hard  water,        .          .          .          .26-88 

*  Analyst,  1912,  xxxvii.,  123. 

12 


178     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

In  the  case  of  vinegars  brewed  with  very  hard  water 
Chapman  found  that  almost  the  whole  of  the  phosphoric 
acid  was  left  in  an  insoluble  condition  (tribasic  calcium 
phosphate)  on  ignition  of  the  total  solids. 

For  these  reasons  he  deprecates  the  fixing  of  an  official 
standard  for  phosphoric  acid  in  vinegar. 

In  like  manner,  the  proportion  of  nitrogen  is  influenced 
by  the  conditions  of  brewing.  If  low-dried  malt  and  low 
mashing  temperatures  be  used,  the  nitrogen  will  be 
higher  than  if  high-dried  malts  are  employed,  or  part  of 
the  wort  be  boiled  after  mashing,  as  is  sometimes  done 
to  promote  the  final  filtration  of  the  vinegar.  The  addi- 
tion of  ferrocyanide  as  a  clarifying  agent  (see  p.  131) 
precipitates  proteins,  and  this  reduces  the  proportion  of 
nitrogen,  and  these  instances  afford  further  illustrations 
of  the  dangers  mentioned  by  Chapman  (loc.  cit.)  "  of 
setting  up  official  standards  for  the  composition  of  manu- 
factured foodstuffs/' 

Optical  Standard. — In  1906  malt  vinegar  was  defined 
by  the  United  States  Department  of  Agriculture  (Circular 
No.  19)  as  "  a  product  made  by  the  alcoholic  and 
subsequent  acetous  fermentations,  without  distillation, 
of  an  infusion  of  barley  malt,  or  cereals  whose 
starch  has  been  converted  by  malt,  is  dextro-rotatory, 
and  contains  in  100  cubic  centimetres  (20°  C.)  not 
less  than  4  grammes  of  acetic  acid,  not  less  than 
2  grammes  of  solids,  and  not  less  than  two-tenths 
(0-2)  gramme  of  ash ;  and  the  water-soluble  ash 
from  100  c.c.  of  the  vinegar  contains  not  less  than 
9  milligrammes  of  phosphoric  acid  (P205),  and  re- 
quires not  less  than  4  c.c.  of  ^  acid  to  neutralise  its 
alkalinity/' 


CHARACTERISTICS   OF   DIFFERENT   VINEGARS.          179 

It  has  been  shown  by  Chapman  *  that  vinegar  brewed 
from  barley  malt  and  cereals  need  not  necessarily  be 
dextro-rotatory,  but  that  the  proteins  and  their  hydro- 
lytic  products  may  cause  the  vinegar  to  show  a  Isevo- 
rotation.  For  example,  practically  the  whole  of  a  manu- 
facturer's stock  of  vinegar  showed  a  Isevo-rotation  of 
—0-56°  to  —0-76°  when  examined  in  a  200  mm.  tube, 
although  no  sugar  had  been  used  in  the  brewing. 

The  Malt  Vinegar  Question. — Few  problems  that  have 
arisen  in  the  administration  of  the  Food  and  Drugs  Acts 
have  presented  more  difficulties  than  the  question  of 
what  is  or  is  not  "  malt  vinegar,"  for  there  is  no  legal 
definition  of  the  product,  and  all  attempts  to  obtain  a 
binding  decision  have  hitherto  proved  fruitless. 

As  far  back  as  1894  the  subject  came  into  prominence 
in  connection  with  certain  vinegar  prosecutions  in  the 
Midlands,  and  a  Conference  of  the  Society  of  Public 
Analysts  f  was  held  with  the  idea  of  obtaining  some 
concerted  agreement  upon  the  point. 

In  the  course  of  the  discussion  it  soon  became  evident 
that  there  was  a  great  divergence  in  the  views  held  by 
leading  Public  Analysts  on  this  subject.  For  example, 
while  one  speaker  held  that  "  malt  vinegar  "  ought  to  be 
derived  solely  from  malted  barley,  a  second  was  pre- 
pared to  pass  a  product  brewed  from  a  mixture  of  10  per 
cent,  of  malt  and  90  per  cent,  of  barley,  and  a  third 
remarked  that  "  no  one  would  doubt  for  a  moment  but 
that  '  malt '  was  a  term  applied  to  a  mixture  of  malt 
and  barley  only/'  Still  greater  latitude  was  allowed  by 
another  Public  Analyst,  who  urged  the  Society  to  adopt 
the  view  that  malt  vinegar  was  "  a  product  initiated  by 

*  Analyst,  1912,  xxxvii.,  123.  t  Analyst,  1894. 


180     VINEGAR  :    ITS    MANUFACTURE   AND    EXAMINATION. 

malt  alone  ;  raw  grain  may  be  used  with  it  in  the  mash- 
tun,  because  the  utilisation  of  its  starch  is  absolutely 
restricted  to  the  action  of  the  malt,  and  therefore  the 
constituents  of  the  wort  may  be  said  to  be  strictly  malt 
products/'  He  would  not  admit  "  the  products  of  starch 
hydrolysed  by  sulphuric  acid  or  in  other  ways  than  by 
diastase." 

The  desirability  of  some  agreement  being  reached, 
both  in  the  interest  of  the  profession  and  of  the  public, 
was  pointed  out  by  more  than  one  speaker,  while  Mr. 
A.  H.  Allen  remarked  that  he  regretted  that  the  vinegar 
manufacturer  had  sometimes  been  hardly  dealt  with  by 
the  Public  Analyst. 

It  was  hardly  surprising,  however,  in  view  of  the 
divergency  of  opinions,  that  the  discussion  should  have 
ended  without  any  definition  of  "  malt  vinegar  "  having 
been  formulated  by  the  Society. 

The  result  has  been  that  individual  Public  Analysts 
when  called  upon  to  examine  samples  of  malt  vinegar 
have  had  to  form  their  own  definitions  and  fix  their  own 
standards,  and  conflicting  decisions  which  settle  nothing 
are  constantly  being  given  in  the  police  courts  all  over 
the  country. 

For  example,  it  was  decided  some  years  ago  in  the 
North  of  England  that  a  vinegar  manufactured  from  a 
mixture  of  malt  and  flaked  maize  was  "  malt  vinegar," 
and  costs  were  allowed  against  the  county  authori- 
ties, whereas  in  1912  a  Worcestershire  bench  held  that 
flaked  maize  or  maize  grits  ought  not  to  be  a  constituent 
of  malt  vinegar,  and  fined  the  defendants. 

We  have  thus  the  farcical  position  that  a  man  is  re- 
garded as  an  honest  man  for  selling  in  one  part  of  England 


CHARACTERISTICS   OF   DIFFERENT  VINEGARS.          181 

an  article  for  the  sale  of  which  in  another  county  he  would 
be  subjected  to  a  criminal  prosecution. 

The  want  of  some  authoritative  statement  has  been 
so  keenly  felt  that  in  1911  the  Association  of  Vinegar 
Brewers  requested  the  Local  Government  Board  to  fix 
a  definition  for  malt  vinegar.  The  Board  replied  (Dec. 
15th,  1911),  that  they  had  no  power  to  fix  legal  definitions 
for  vinegar,  but  they  suggested  definitions  that  might 
be  acceptable  to  all  concerned  in  the  manufacture  and 
examination  of  vinegars,  viz.  :— 


"GENERAL  STANDARD  FOR  VINEGAR. 

"  Vinegar  is  a  liquid  derived  wholly  from  alcoholic 
and  acetous  fermentations ;  it  shall  not  contain  less 
than  4  grammes  of  acetic  acid  (CH3  .  COOH)  in  100  cubic 
centimetres  of  vinegar  ;  it  shall  not  contain  arsenic  in 
amounts  exceeding  0-0143  milligramme  per  100  cubic 
centimetres  of  vinegar,  nor  any  sulphuric  or  other  mineral 
acid,  lead  or  copper,  nor  shall  it  contain  any  foreign 
substance  or  colouring  matter  except  caramel.  Malt 
vinegar  is  derived  wholly  from  malted  barley  or  wholly 
from  cereals,  the  starch  of  which  has  been  saccharified 
by  the  diastase  of  malt. 


-ARTIFICIAL  VINEGAR. 

"  Artificial  Vinegar  is  any  vinegar  or  substitute  for 
vinegar  containing  or  derived  from  any  preparation 
containing  any  added  acetic  acid  which  is  not  wholly 
the  product  of  alcoholic  and  subsequent  acetous  fer- 


182     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

mentation.  It  shall  contain  not  less  than  4  grammes 
of  acetic  acid  (CH3 .  COOH)  in  100  cubic  centimetres  of 
the  artificial  vinegar.  It  shall  not  contain  arsenic  in 
amounts  exceeding  0-0143  milligramme  per  100  cubic 
centimetres  of  vinegar,  nor  any  sulphuric  or  other  mineral 
acid,  lead  or  copper,  nor  shall  it  contain  any  foreign 
substance  or  colouring  matter  except  caramel." 

It  will  be  seen  that  this  definition  for  malt  vinegar 
restricts  the  use  of  the  term  to  the  products  of  the  mash- 
tun,  and  excludes  those  made  by  the  conversion  process. 
It  thus  supports  the  view  put  forward  by  several  public 
analysts  that  the  term  "  malt  "  should  refer  to  the  agency 
by  which  the  starch  of  the  grain  is  hydrolysed. 

On  the  other  hand,  it  permits  the  use  of  any  cereal 
(including  rice  or  maize),  provided  that  sufficient  malted 
grain  is  present  to  effect  the  hydrolysis. 

Unfortunately,  this  definition  has  not  been  generally 
accepted  by  Public  Analysts,  for  since  it  appeared  there 
have  been  several  prosecutions  for  the  sale  of  vinegars 
derived  in  part  from  products  other  than  malt,  and 
there  has  been  the  usual  result  of  conflicting  decisions 
by  magisterial  benches  in  different  parts  of  the  country. 
It  is  to  be  hoped  that  before*  long  this  definition  may  be 
legalised  by  statute  so  as  to  put  an  end  to  the  present 
state  of  uncertainty  and  confusion. 

The  following  analyses,  made  by  the  writer,  show  the 
characters  of  the  products  sold  as  malt  vinegar  by 
leading  manufacturers,  the  samples  having  been  bought 
at  various  times  during  the  last  twelve  years  : — 


COMPOSITION   OF   MALT   VINEGARS. 


183 


§•3* 


000 


S-O^  I  5  I>  CO  t'  CO 
"3,'S  C,  !  uO^OO 
O  ^  ;  ^ 


CO  GO  CO  tO         t>         00 


I     - 


>— iC<|j— IP^I-HI— (C-li— i  i— le^f^S^C^i— i  I-H 

ooooooooooooooo 


184     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

Vinegars  made  by  the  same  manufacturers  as  Nos. 
IV.,  XII.,  and  XV.,  and  giving  similar  analytical  results, 
have  been  made  the  subjects  of  prosecution,  on  the 
grounds  of  not  being  wholly  malt  products.  The  low 
nitrogen  and  phosphoric  acid  results  were  attributed  by 
the  defence  to  the  use  of  cereals  other  than  malted  barley- 
In  some  cases  there  were  acquittals  and  in  others  con- 
victions. 

The  vinegar  No.  XI.  was  remarkably  high  in  nitrogen 
and  abnormally  low  in  phosphates,  and  for  this  reason 
the  makers  were  prosecuted,  but  won  their  case.  The 
explanation  of  the  abnormal  figures  is  that  the  vinegar 
was  brewed  from  a  mixture  of  green  malt  and  rice,  the 
former  being  responsible  for  the  high  nitrogen  and  the 
latter  for  the  low  phosphoric  acid. 

Several  of  the  vinegars  included  in  the  above  table 
were  admittedly  manufactured  by  the  conversion  process. 
No.  XVI.  was  a  typical  instance,  and  it  was  characterised 
by  a  high  percentage  of  mineral  matter,  in  which,  too, 
there  was  a  large  proportion  of  sulphate. 

The  low  proportion  of  total  solids  in  No.  IX.  is  unusual, 
and  has  on  more  than  one  occasion  been  the  subject  of 
comment.  It  could  be  satisfactorily  accounted  for  by 
the  fermentation  having  been  carried  to  a  lower  point 
than  is  usually  the  case. 

CIDER  VINEGAR. 

Very  little  cider  vinegar  is  manufactured  in  this 
country,  but  in  the  United  States  it  is  in  much  greater 
demand  than  either  wine  or  malt  vinegar. 

Analyses   of   twenty-two   typical   samples   of   various 


CHARACTERISTICS    OF   DIFFERENT   VINEGARS.          185 

origin  were  published  by  Leach  and  Lythgoe,*  and  from 
their  results  they  suggest  that  certain  chemical  standards 
should  be  fixed.  Thus,  in  their  opinion,  pure  cider  vinegar 
should  contain  at  least  4-5  per  cent,  of  acetic  acid  and 
2  per  cent,  of  ash  (which  should  be  at  least  6  per  cent, 
of  the  total  solids,  and  have  an  alkalinity  equivalent  to 
at  least  65  c.c.  ~  acid  per  1  grm.).  Not  less  than  50  per 
cent,  of  the  phosphates  should  be  soluble  in  water.  The 
reducing  sugars  should  not  vary  in  amount  after  inversion, 
and  should  not  exceed  25  per  cent,  of  the  total  solids. 
The  specific  rotation  of  the  clarified  vinegar  should  be 
between  -0-1°  and  -4-0°  Ventske  (200  mm.  tube). 
The  presence  of  malic  acid  should  be  ascertained  by  the 
lead  acetate  and  calcium  chloride  tests  (see  p.  154). 

In  the  opinion  of  Tolman  and  Goodnow,t  the  older 
analyses  of  cider  vinegar  are  not  applicable  to  the  vinegars 
which  are  now  being  made  by  the  "  quick  "  process. 
Their  experiments  indicated  that  the  loss  in  volume 
during  acetification  was  so  small  that  it  was  possible, 
without  correction,  to  compare  the  results  with  those 
given  by  the  original  cider.  This  contained  on  the  average 
7-7  per  cent,  by  volume  of  alcohol  and  0-27  per  cent,  of 
acetic  acid,  and  yielded  a  vinegar  containing  5-77  per 
cent,  of  acetic  acid  and  0-4  per  cent,  of  alcohol,  the  loss 
of  alcohol  during  acetification  being  thus  over  20  per 
cent. 

The  total  solids,  ash,  and  glycerin  were  but  little 
affected  by  acetification,  while  the  non-sugars  were  sub- 
stantially the  same  in  the  cider  and  the  vinegar.  Alde- 
hydic  compounds  were  formed,  and  it  was  necessary  to 

*  J.  Amer.  Chem.  Soc.,  1904,  xxvi.,  375. 
t.7.  Ind.  Eng.  Chem.,  1913,  v.,  928. 


186    VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

evaporate  the  vinegar  repeatedly  to  expel  these  ;  other- 
wise the  sugars  were  overestimated  by  Fehling's  solution 
by  0-15  to  0-2  grm.  per  100  c.c. 

The  fixed  acids  were  greatly  reduced  by  acetification, 
and  fell  as  low  as  0-04  per  cent,  (as  malic  acid)  ;  on  the 
other  hand,  the  pentosans  increased  by  about  50  per 
cent. 

The  following  analysis  of  a  French  cider  vinegar  is 
given  by  Calvet  *  : — Total  acidity  as  acetic  acid,  4-71 ; 
fixed  acidity  (as  H2S04),  0-19;  total  solids,  1-98;  re- 
ducing sugars  (as  dextrose),  0-27  ;  ash,  0-26  ;  and  alcohol, 
0-7  per  cent. 

WINE  VINEGAR. 

Wine  vinegar  is  the  predominating  product  of  France, 
just  as  malt  vinegar  is  in  this  country,  and  cider  vinegar 
in  the  United  States.  Red  or  white  wines  are  used  in 
the  manufacture,  and  the  resulting  vinegars  accordingly 
vary  in  colour. 

As  a  rule,  the  acetic  strength  is  considerably  higher 
than  in  the  case  of  malt  vinegar,  and  is  usually  not  less 
than  7  or  8  per  cent.  The  specific  gravity  is  low,  owing 
to  the  small  amount  of  solid  matter  present. 

An  analysis  made  by  the  writer  of  one  of  the  principal 
French  wine  vinegars  sold  in  this  country  gave  the  fol- 
lowing results  : — Specific  gravity,  1-017;  acetic  acid, 
7-2;  total  solids,  1-7  ;  ash,  0-25;  phosphoric  acid,  0-042; 
and  nitrogen,  0-013  per  cent. 

Vinegars  made  from  British  wines  contain  more  total 
solids  than  French  wine  vinegars,  and  these  are  of  a  more 

*  LOG.  cit.,  p.  61. 


CHARACTERISTICS    OF   DIFFERENT   VINEGARS. 


187 


viscous  character  from  the  presence  of  the  sugar  in  the 
wine. 

The  distinguishing  characteristics  of  genuine  grape 
wine  vinegars  are  the  presence  of  tartaric  acid  and  inositol, 
for  the  detection  of  which  see  pp.  155,  153. 

The  following  results  were  obtained  in  the  analysis  of 
white  wine  vinegars  by  the  Municipal  Laboratory  of 
Paris  : — 


j   Specific 
j  Gravity. 

Total 
Solids. 

Sugar. 

Potassium 
Bitartrate. 

Ash. 

Acetic 
Acid. 

I 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

Maximum,        1-0213 

3-19          0-46 

0-36 

0-69 

7-38 

Minimum, 

1-0129 

1-38          0-56 

0-07 

0-16 

4-44 

Mean, 

1-0175        1-93          0-22 

0-17 

0-32 

6-55 

The  presence  of  glucose  vinegar  in  wine  vinegar  may 
be  detected,  according  to  Delluc,*  by  the  fact  that  in  the 

OY'i'T'Q  r*4- 

former  the  ratio  of  -^ approximates  to  unity.     This 

dextrose 

is  shown  by  the  following  analyses  of  white  and  red 
vinegars  made  from  coloured  glucose  syrups  :— 


White  Vinegar. 

Red  Vinegar. 

Specific  gravity  at  15°  C., 
Acetic  acid,  per  cent.,       .          .          . 
Total  solids,  per  cent., 
Reducing  sugars,  as  dextrose,    . 

total  solids 
T?itio 

1-025 
6-65 
2-41 
2-26 

1-06 

1 

1-012 
4-20 
1-12 
0-98 

1-14 

dextrose 

For  the  method  of  determining  reducing  sugars,  see 
p.  152. 

*  Calvet,  loc.  cit.,  p.  61. 


188     VINEGAR  :    ITS   MANUFACTURE   AND    EXAMINATION. 

Wine  vinegars  are  frequently  adulterated  in  France 
with  spirit  vinegar  ;  or,  rather,  the  vinegar  is  prepared 
by  acetifying  a  mixture  of  wine  and  dilute  alcohol. 

Distilled  wine  vinegar  is  made  by  distilling  either 
red  or  white  wine  vinegar  under  reduced  pressure  (see 
p.  135).  It  is  commonly  sold  under  the  name  of  white 
wine  vinegar,  and  this  name  is  also  wrongly  applied  to 
distilled  malt  vinegar. 

WHEY  VINEGAR. 

This  is  made  from  the  whey  of  milk  fortified  with 
sufficient  sugar  to  give  the  alcohol  necessary  for  the 
production  of  the  acetic  acid. 

A  sample  examined  by  Filaudeau  and  Vitoux  *  had  the 
following  characters  : — Specific  gravity  at  15°  C.,  1-0184  ; 
total  acidity  as  acetic  acid,  6-51  ;  fixed  acidity  as  lactic 
acid,  0-18  ;  total  solids,  2-10  ;  reducing  sugars,  as  lactose, 
1-44;  nitrogenous  substances  as  casein,  0-17;  ash, 
0-14  ;  sodium  chloride,  0-09  ;  and  insoluble  ash  (tribasic 
calcium  phosphate),  0-11  per  cent. 

FRUIT  AND  HERB  VINEGARS. 

Vinegar  may  be  made  from  any  fruit  containing  suffi- 
cient sugar  for  the  production  of  the  necessary  alcohol. 

In  other  cases — e.g.,  raspberry  vinegar — the  vinegar 
is  made  by  steeping  the  fruit  in  distilled  vinegar  and 
sweetening  the  product  with  cane  sugar. 

A  similar  process  is  employed  in  preparing  tarragon 
and  other  products  of  the  same  nature,  the  herbs  being 

*  Ann.  des  Falsificat.,  1909,  ii.,  208. 


CHARACTERISTICS   OF   DIFFERENT   VINEGARS. 


189 


steeped  in  a  brewed  or  distilled  vinegar  to  impart  the 
necessary  flavour. 

DATE  VINEGAR. 

A  few  years  ago  a  spirited  attempt  was  made  in  this 
country  to  create  a  demand  for  date  vinegar  in  place  of 
malt  vinegar.  The  products  put  upon  the  market  had  a 
characteristic  flavour  and  aroma,  somewhat  recalling  that 
of  a  wine  vinegar. 

Compared  with  a  normal  barley  malt  vinegar,  they 
were  low  in  nitrogen  and  phosphoric  acid.  Three  com- 
mercial samples  examined  by  the  writer  in  different 
years  gave  the  following  percentage  results  :— 


Acetic  Acid. 

Total  Solids. 

Ash. 

Phosphoric  Acid. 

Nitrogen. 

I. 

5-0 

2-61 

0-48 

0-051 

0-031 

II. 

5-34 

2-80 

0-49 

0-052 

0-024 

III. 

5-8 

2-47 

0-49 

0-038 

0-030 

. 

In  spite  of  much  advertising,  date  vinegar  never 
became  a  serious  competitor  of  malt  vinegar,  and  of 
late  years  appears  to  have  disappeared  from  the  market. 

SPIRIT  VINEGARS. 

The  manufacture  of  vinegar  from  dilute  alcohol  has 
become  a  serious  competitor  of  the  old-established  in- 
dustry of  wine  vinegar  in  France,  since  the  product  can 
be  sold  at  a  much  lower  price. 

Spirit  vinegar  is  usually  coloured  with  a  little  caramel, 
to  make  it  resemble  wine  vinegar  more  closely.  Its 
odour  is  much  more  pungent,  and  lacks  the  bouquet 


190    VINEGAR:  ITS  MANUFACTURE  AND  EXAMINATION. 

of  the  wine  product.  It  contains  much  less  solid  matter 
and  ash  than  wine  vinegar,  but  differs  from  dilute  acetic 
acid  in  containing  alcohol,  aldehyde,  and  tartaric  acid. 

The  following  analysis  shows  the  composition  of  a 
typical  French  product : — Total  acidity  as  acetic  acid, 
7-68  ;  fixed  acidity  (as  H2S04),  0-03  ;  total  solids,  0-22  ; 
tartaric  acid,  0-08  ;  and  ash,  0-04  per  cent.  ;  ratio  : 

fxtract,  34-9. 
dextrose 

Essigsprit  or  Vinegar  Essence. — A  German  product  is 
prepared  from  potato  spirit  by  a  fermentation  process. 
It  usually  contains  about  11  to  12  per  cent,  of  acetic 
acid,  and  has  a  slight  yellow  tint,  and  an  agreeable  aro- 
matic odour.  Until  recently,  it  was  imported  into  this 
country  in  large  quantities,  and  used  for  pickling  purposes 
as  a  cheap  substitute  for  malt  vinegar. 

A  typical  sample  examined  by  the  writer  had  the 
following  characteristics  : — Acetic  acid,  12-3  ;  total  solids, 
0-16  ;  and  ash,  0-02  per  cent. 

A  concentrated  acetic  acid  is  also  made  by  neutralising 
the  Essigsprit  with  lime  and  distilling  the  calcium  acetate 
with  sulphuric  acid.  Spirit  acid  thus  prepared  has  a  much 
more  pleasant  aroma,  and  contains  fewer  impurities  than 
much  of  the  wood  acetic  acid  imported  into  England. 

WOOD  VINEGAR. 

Wood  vinegar,  as  its  name  denotes,  is  nothing  more 
than  dilute  acetic  acid,  coloured  with  caramel,  and 
sometimes  flavoured  by  the  addition  of  a  small  quantity 
of  brewed  vinegar. 

It  has  a  pungent  odour  of  acetic  acid,  and  lacks  the 


CHARACTERISTICS   OF   DIFFERENT   VINEGARS. 


191 


aroma  of  malt  vinegar,  although  it  is  frequently  fraud- 
ulently sold  under  the  name  of  "  malt  vinegar/' 

The  following  analyses  of  commercial  samples  of 
artificial  vinegar  were  made  by  the  writer  during  the 
last  ten  years  : — 

COMPOSITION  OF  ARTIFICIAL  VINEGARS. 


Colour 

Sold  as 

Specific 
Gravity 
at  155°  C. 

Acetic 
Acid. 

Total 
Solids. 

Ash. 

Phos- 
phoric 
Acid. 

Nitrogen. 

Lovi- 
bond. 

"52" 

Series. 

Per 

Per 

Per 

Per 

Per 

Per 

cent. 

cent. 

cent. 

cent. 

cent. 

cent. 

"  Wood 

vinegar," 

1-009 

4-9 

0-52 

0-03 

0-02 

0-009 

24 

"  Pale    malt 

vinegar," 

5-2 

0-18 

0-018 

trace 

0-008 

1-5 

"  Double  re- 

fined malt 

vinegar," 

1-006 

4-4 

0-60 

0-036 

0-005 

none 

.  . 

"  Malt 

vinegar," 

•• 

4-25 

0-65 

0-24 

trace 

trace 

'  •  •:,  ". 

In  the  case  of  the  "  double  refined  malt  vinegar/'  the 
whole  of  the  colouring  matter  could  be  precipitated  by 
fuller's  earth,  but  this  was  not  possible  with  the  last 
sample.  It  was,  therefore,  probable  that  in  the  latter 
vinegar  some  of  the  colour  was  derived  from  the  addition 
of  grain  vinegar  as  a  flavouring  agent. 

The  traces  of  phosphoric  acid  and  nitrogen  were  pro- 
bably present  in  the  caramel  used  for  colouring  these 
products.  The  high  ash  of  the  last  sample  was  due  to 
the  presence  of  0-18  per  cent,  of  common  salt. 

Artificial  vinegars  usually  contain  at  least  4  per  cent, 
of  acetic  acid,  and  there  have  been  numerous  prosecutions 
for  the  sale  of  products  of  lower  acidity  (see  p.  172). 


192 


APPENDIX  I. 

IMPORT   DUTIES   ON  VINEGAR   AND   ACETIC 
ACID. 

British  India- 
Vinegar  in  casks,        .          .          .          .          •     2£  per  cent,  ad  valorem. 
Vinegar  not  in  casks,  .          .          .          .5  .,  „ 

Ceylon- 
Vinegar  in  casks,        .....     2|         „  ,. 
Vinegar  not  in  casks,           .          .          .          •     5£        ,,  „ 

Mauritius- 
Vinegar  not  exceeding  8  degrees  by  Salleron's 

acetimetre,     ....         per  gall.         Rs.  .0     7TST  cts. 
(With  an  additional  duty  of  T9T  cts.  for  every  degree 
above  8  degrees  by  Salleron's  acetimetre.)* 

Seychelles,        .         .         .         .         .  .   12 1  per  cent,  ad  valorem. 

Australia- 
Vinegar,  vinegar  essence,  and  acetic  acid  vinegar  (standard 
as  prescribed  by  Departmental  Bye-laws),  the  product  of 
malt,  grain,  or  fruit  juice  by  alcoholic  and  acetic  fermenta- 
tion, containing  not  more  than  6  per  cent,  of  absolute 

acetic  acid, per  gall.    £006 

Vinegar  not  the  product  of  malt,  grain,  or  fruit  juice,  per  gall.     020 
Solutions  containing  more  than  6  per  cent.,  but  less  than 

30  per  cent., per  gall.      039 

For  every  10  per  cent,  additional,     .          .          .  ,,          013 

Papua- 
All  kinds,       per  gall.      006 

*  See  p.  138. 


APPENDIX    I.  193 

New  Zealand- 
Vinegar  not  exceeding  6-5  per  cent,  of  acidity  as  acetic  acid, 

per  gall.  006 

Otherwise, 0    0    7J 

Acetic  acid  up  to  30  per  cent,  strength,    .          .        per  Ib.  00     1$ 

For  every  10  per  cent,  additional  acidity,  .  „  0    0    OJ 

Fiji, per  gall.      006 

British  South  Africa- 
Glacial  acetic  acid — 

(1)  In  bottles,  etc.,  not  exceeding  an  imperial  quart — 

Under  British  preferential  tariff,  .     per  gall.    £146 

Under  general  tariff,  .          .          .          .  „  1  12     5 

(2)  In  larger  quantities — 

British  preferential  tariff,    ...  „  140 

General  tariff, „  1  11  11 

Vinegar,  vinegar  essence,  acetic   (other  than  glacial)  and 
pyroligneous  acids,  not  exceeding  proof  strength — 

(1)  In  bottles,  etc.,  not  exceeding  1  quart — 

British  preferential  tariff, £010 

General  tariff,    .         .         .         .         .         .         .011 

(2)  In  larger  quantities — 

British  preferential  tariff,    .         .         .         .         .006 

General  tariff,    . 007 

And  in  addition  in  either  case  for  each  degree  of  strength  in 
excess  of  proof — 

Under  British  preferential  tariff,         .         .  per  degree  £003 
Under  general  tariff,          .          .          .       "  .•'        „  004 

(Note. — "  Proof  "  will  be  held  to  be  equal  to  6  per  cent,  of  absolute  acetic 
acid,  and  shall  be  determined  in  the  manner  prescribed  by  the  Customs. 
In  Cape  of  Good  Hope,  the  sale  is  prohibited  of  vinegar  to  which  have 
been  added  ingredients  injurious  to  health,  and  which  does  not  contain 
at  least  3£  per  cent,  of  absolute  acetic  acid  (Act  No.  19  of  1908).) 

Nyasaland  Protectorate,      .        .        .        .        .     10  per  cent,  ad  valorem. 

Uganda  Protectorate, 10      „ 

British  East  Africa, 10      „ 

Somaliland— 

Imported  in  Zeyla, 5       „  „ 

Imported  in  other  ports,       ....?„  „ 

13 


194     VINEGAR  I    ITS   MANUFACTURE   AND    EXAMINATION. 

Nigeria, 10  per  cent,  ad  valorem. 

Gold  Coast — 

Imported  west  of  the  Volta,          .         .         .     10      „  „ 

Imported  east  of  the  Volta,  .         .         .       4       „  „ 

Sierra  Leone, 10      „  „ 

Gambia, .      5      „  „ 

Canada- 
Vinegar  and  acetic  acid  (not  exceeding  proof  strength — 

Under  British  preferential  tariff,     .         .     per  gall.     £0    0    4-93 
Under  intermediate  tariff,       .         .         .  „  0    0    6-17 

Under  general  tariff,      .         .         .         .  „  0    0     7-40 

With  additional  duties  of  0-74d.,  0-86d.,  and  0-99d.  for  each 

degree  under  proof. 

(The  strength  of  proof  shall  be  held  to  equal  6  per  cent,  of  absolute  acetic 
acid,  and  shall  be  determined  in  the  manner  prescribed  by  the  Governor  - 
in-Council.) 

Newfoundland— 

In  cask, .per  gall.     £0     0     7-40 

In  bottle, 30  per  cent,  ad  valorem. 

Bahamas,          .  •  .  20      „  „ 

Jamaica,  ......  .  16f    „ 

St.  Lucia, per  gall.        £004 

St.  Vincent,        .  10  per  cent,  ad  valorem. 

Barbados,          ....  .  10      „ 

Grenada, .  10      „ 

Virgin  Islands, per  gall.       £003 

St.  Christopher,          .  ,,004 

Antigua, »  004 

Monserrat,         ....  „  004 

Dominica, 003 

Trinidad  and  Tobago- 
Acetic  acid  below  6  per  cent,  strength,           .  per  gall.  £006 
Acetic  acid  above  6  per  cent,  strength,                      „  026 
Vinegar, „  006 


APPENDIX    t.  195 

Bermuda- 
All  kinds,  ........    10  percent,  ad  valorem. 

British  Honduras- 
All  kinds,  12£    „ 

British  Guiana— 

Vinegar,  containing  less  than  10  per  cent,  of  acetic  acid, 

per  gall.        £005 
Malta— 

Per  barrel  of  9£  gallons,       .         .....         .         .        020 

Cyprus- 
All  kinds, .     8  per  cent,  ad  valorem. 

No  import  duties  are  charged  in  the  following  countries  : — 

Aden,    Straits    Settlements,    Hong-Kong,    Falkland    Islands,    N.E. 
Rhodesia,  St.  Helena,  and  Gibraltar. 


196 


APPENDIX  II. 
FRENCH  DUTIES  ON  VINEGAR. 


PRIOR  to  the  year  1872  the  only  vinegar  upon  which  duty  was  charged  in 
France  was  that  made  from  beer,  the  raw  materials  for  which  were  taxed 
in  accordance  with  a  law  of  1816.  The  duty  levied  in  1872  upon  alcohol 
intended  for  the  manufacture  of  spirit  vinegar  led  to  complaints  from  the 
vinegar  makers  of  the  unfair  advantage  given  to  the  manufacturers  of 
wine  vinegar,  with  the  result  that  in  1 875  a  uniform  tax  was  imposed  upon 
vinegar  of  every  description  in  accordance  with  the  following  tariff.  The 
strength  of  the  vinegar  is  based  upon  the  results  obtained  with  Salleron's 
acethnetre  (p.  138). 

FRENCH  DUTIES  ON  MANUFACTURED  OR  IMPORTED  VINEGAR. 


Frail  cs. 
5 

7-50 
10 


1.  Vinegars  containing  8  per  cent,  or  less  acetic  acid, 

„  „          9  to  12  per  cent,  acetic  acid, 

„  „        13  to  16  per  cent,  acetic  acid, 

2.  Acetic  acids  and  vinegars  containing  17  to  30  per  cent. 

acetic  acid, 18-75 

Acetic  acids  and  vinegars  containing  31  to  40  per  cent. 

acetic  acid,       .          .          .          .          .          .          .25 

Acetic  acids  and  vinegars  containing  more  than  40  per 

cent,  acetic  acid,       ......  52-52 

3.  Glacial  acetic  acid  in  the  solid  condition,  .          .  62 -50  per  100  kilos. 


per 
hecto- 
litre. 


197 


INDEX. 


Acetal,  52. 
Acetaldehyde,  52. 
Acetates  of  lime,  66. 
Acetic  acid,  Anhydrous,  59. 

Boiling  point  of,  76. 

from  lime  acetate,  66. 

verdigris,  62. 

wood,  65. 

•  Glacial,  61. 

Manufacture  of,  62,  66. 

—  Optical  refraction  of,  174. 

Oxidation  of,  55. 

Pharmacopceial,     57,    58, 

74. 

— •  Properties  of,  70. 
— •  Radical,  60. 

—  Real,  16,  17,  60. 

—  Specific  gravity  of,  76. 

—  bacteria,  32. 
enzymes,  30. 

strength,  137,  172. 

Acetification,  Chemical  reactions  in, 

50. 
Early  theories  of,  20. 

—  in  practice,  115. 

Orleans  process  of,  100. 

•  Oxidation  in,  50. 

—  Quick  process  of,  105. 

Slow  process  of,  99. 

Acetifiers,  105. 
Acetimetre,  138,  192. 
Acetites,  58. 
Acetometer,  14,  139. 
Acetous  acid,  58. 
Acetum,  1. 

distillatum,  57. 

Acetylic  acid,  60. 

Acidity,  Determination  of,  137. 

Standards  of,  139. 


Aeration  of  acetifiers,  1.16. 

devices,  110. 

tubes,  112. 

Alchymy,  1. 

Alegar,  7. 

Alkalinity  of  ash.  141. 

Alkalised  vinegar,  3,  57. 

Analysis  of  vinegar,  137. 

Aniline  colours,  157. 

Antigua  vinegar  duties,  194. 

Archil,  163. 

Arsenic  Committee,  166. 

Estimation  of,  166. 

in  vinegar,  164. 


Artificial  vinegar,  191. 

Definition  of,  181,  192. 

Australian  vinegar  duties,  192. 
standards,  172,  192. 


B 


Bacillus  aceti  vini,  43. 

acetigenus,  42. 

acetosus,  42. 

•  curvus,  42. 

—  Orleanensis,  42. 

oxydans,  42. 

rancens,  43. 

Schutzenbachii,  43. 

vini  acetati,  43. 

xylinoides,  43. 

xylinus,  41,  47,  54. 

Bacteria,  Acetic,  32. 

Action  of  light  on,  44. 

Involution  forms  of,  36. 

Pure  cultures  of,  47. 

Bacterial  theories  of  acetification,  27, 

32. 

Bacterium  aceti,  31,  33. 
Enzyme  of,  31. 


198 


INDEX. 


Bacterium  Kutzingianum,  33. 

Pasteurianum,  33. 

Barbados  vinegar  duties,  194. 
Beaufoy's  vinegar  works,  9. 
Bermuda  vinegar  duties,  194. 
Bersch's  acetifier,  114. 
Berzelius'  theory  of  acetificatlon,  20. 
Boerhave's  process,  6,  7. 
Boorde's  dyetary,  7. 
British  Guiana  duties,  195. 
—  Honduras  duties,  195. 

—  India  duties,  192. 

—  East  Africa  duties,  193. 
South  Africa  duties,  193. 

Buchner's  acetic  enzymes,  30. 


Canada  vinegar  duties,  194. 
Caramel  in  vinegar,  150,  181. 

Detection  of,  159. 

Estimation  of,  162. 

Catalytic  theory  of  acetification,  20. 

Ceylon  vinegar  duties,  192. 

Chemical  standards  for  vinegar,  171. 

Cider  vinegar,  184. 

Citric  acid  in  vinegar,  156. 

Clarification  of  vinegar,  130. 

Claudon's  apparatus,  103. 

Cochineal,  162. 

Coloured  wine  vinegar,  162. 

Colouring  matters,  156. 

Colour  measurement,  157. 

Conversion  process,  89. 

Copper  in  vinegar,  163. 

Crystals  of  Venus,  63. 

Cyprus  vinegar  duties,  195. 


Date  vinegar,  189. 
Diamond  vinegar,  19. 
Distillation  of  vinegar,  135. 

Early  apparatus,  3. 

— • —  of  radical  vinegar,  63. 
Distilled  verdigris,  62. 

vinegar,  136. 

Domestic  manufacture,  4. 
Dominica  vinegar  duties,  194. 


Dujardin's  acetometer,  139. 
Duties  on  vinegar,  10. 
Colonial  vinegar,  192. 


E 


East  Africa  vinegar  duties,  193. 
Enzyme  of  acetic  bacteria,  29. 
Enzymic    theories    of    acotification. 

22,  27,  28. 
Essig-sprit.  64,  190. 

Composition  of,  190. 

Ethyl  acetate,  53. 
Examination  of  vinegar,  137. 
Excise  Commission  on  vinegar,  9,  13. 

list  of  vinegar  brewers,  11. 

vinegar  duties,  10. 


Fermentation  of  wort,  91. 
Ferrocyanide  precipitation,  131. 
Fiehe's  reaction,  161. 
Fielding,  98. 
Fiji  vinegar  duties,  193. 
Filtration  of  vinegar,  129. 
Fining  of  vinegar,  131. 
Flaked  maize,  86. 

Composition  of,  177. 

rice,  ~" 


Formic  acid  in  vinegar,  150. 
French  vinegar  duties,  196. 
Fruit  vinegars,  188. 
Fuller's  earth  test  for  caramel,  159. 


G 


Gambia  vinegar  duties,  194. 
Gelatinised  grain,  86. 
Gluconic  acid,  54. 
Glucose  vinegar,  187. 
Gold  Coast  vinegar  duties,  194. 
Grenada  vinegar  duties,  194. 
Group  system  of  acetification,  120. 
Gyle,  Acetification  of,  98. 

Distribution  of,  106. 

Preparation  of,  77. 

Storage  of,  97. 


INDEX. 


199 


Hansen's  vinegar  bacteria.  32. 
Hehner's    estimation     of    sulphuric 

acid,  145. 

Hot  liquor  backs,  82. 
Hydrocyanic  acid  in  vinegar,  131. 


I 


Import  duties  on  vinegar,  192. 
Indian  vinegar  duties,  192. 
Inositol  in  wine  vinegar,  153. 
Iron  in  vinegar,  163. 


Jamaica  vinegar  duties,  194. 


Lead  in  vinegar,  163. 

Legislation  on  vinegar,  10. 

Licences  for  vinegar,  13. 

Liebig's  theory  of  acetification,  21, 

25. 

Light,  Action  on  acetic  bacteria,  44. 
Lime  acetates,  66. 

acid,  66. 

Lovibond's  tintometer,  158. 
Luck's  acetifier,  114. 


Maize,  Composition  of,  175. 

Flaked,  177. 

Malic  acid  in  cider  vinegar,  154. 
Malt,  Composition  of,  175. 

vinegar,  179. 

Definitions  of,  178,  181. 

standards,  139,  172,  178. 

—  vinegars,  Composition  of,  183. 

Malta  vinegar  duties,  195. 
Manufacturing  processes,  Early,  5. 
Mashing  machines,  81. 
Process  of,  83. 


Mash-tun,  77. 

Mauritius  vinegar  duties,  192. 

Methyl-acetol,  149. 

Metallic  impurities  in  vinegar,  163. 

Mineral  acids  in  vinegar,  143. 

Montserrat  vinegar  duties,  194. 

Mother-of -vinegar,  20,  117,  121. 

Mucilage  in  vinegar,  14. 

Mycoderma  aceti,  20,  23,  25,  32,  47. 

55. 
mm,  25. 


N 


Nageli's  mechanical  theory,  27. 
New  Zealand  vinegar  duties,  193. 
Newfoundland  vinegar  duties,  194. 
Newton's  apparatus,  70. 
Nigeria  vinegar  duties,  194. 
Nitrogen  in  vinegar,  151,  174. 
Nitrogenous  substances  in   vinegar, 

151. 

Numbers  of  vinegar,  16. 
Nyasaland  vinegar  duties,  193. 


Oats,  Composition  of,  175,  176. 
Optical  standard  for  vinegar,  178. 
Orleans  process,  100. 
Original  solids,  172. 
Otto's  acetometer,  139. 
Oudemann's  acid  table,  75. 
Oxalic  acid  in  vinegar,  156. 
Oxidation,  Chemical  process  of,  68. 
Ozone  in  acetifiers,  69. 


Papua  vinegar  duties,  192. 
Parachute,  Yeast,  95. 
Pasteur's  acetification  theory,  23. 
Pharmacopoeial     requirements     for 
acid,  73. 

vinegar,  17. 

Phosphates  in  vinegar,  174. 

Estimation  of,  152. 

Plate  acetifiers,  115,  117. 


200 


INDEX. 


Platinum    black   oxidation,    51,    56, 

68. 

Popped  barley,  86,  177. 
Precipitation  processes,  131. 
Proof  acid,  16,  193,  194. 

vinegar,  12,  14,  193,  194. 

Prussic  acid  in  vinegar,  132. 
Pyroligneous  acid,  65,  66. 

Estimation  of  strength  of, 

140. 


Quick  process,  105. 


Radical  vinegar,  16,  60. 
Rapes,  129. 

Real  acetic  acid,  16,  17,  60. 
Refrigerators,  91. 
Rozier's  experiment,  51. 
Rye,  Composition  of,  175. 


S 


Salleron's  acetimetre,  138,  196. 
Schultze's  extract  table,  142. 
Seychelles  vinegar  duties,  192. 
Sierra 'Leone  vinegar  duties,  194. 
Singer's  apparatus,  114. 
Siphon  distributors,  109. 
Slow  process,  99. 
Soda  acid,  66,  67. 
Somaliland  vinegar  duties,  193. 
South  Africa  duties,  193. 
Sparge  in  acetifier,  107. 

mash -tun,  80. 

Specific  gravity  of  acetic  acid,  75. 

vinegar,  141. 

Spirit  acid,  190. 

of  vinegar,  3. 

vinegar,  64,  101. 

vinegars,  189. 

St.  Christopher  vinegar  duties,  194. 
St.  Lucia  vinegar  duties,  194. 
St.  Vincent  vinegar  duties,  194. 
Stahl's  theory,  21. 


Standards  for  vinegar,  172. 
Sterilisation  of  vinegar,  132. 
Still  for  vinegar,  135. 

residues,  136. 

Strength  of  vinegar,  19,  61,  139,  172. 
Succinic  acid  in  vinegar,  54. 
Sugar,  Addition  to  wort,  88. 
Estimation  of,  152. 


Sulphates  in  vinegar,  148. 
Sulphuric  acid,  12,  14,  144. 

Combined,  148. 

Estimation  of,  145. 


Tarragon  vinegar,  188. 
Tartaric  acid  in  wine  vinegar,  15o. 
Temperatures  in  acetification,  118. 
Tin  in  vinegar,  163. 
Tintometer,  158. 
Tipping  trough,  108. 
Tobago  vinegar  duties,  194. 
Torrefied  barley,  86. 

Composition  of,  177. 

Total  solids,  140. 

Standard  for,  172. 

Trade  numbers,  16. 
Trinidad  vinegar  duties,  194. 


U 


Uganda  vinegar  duties,  193. 
United  States  vinegar  standard,  17* 
Uvula  aceti,  21. 


Verdigris,  62. 

Vinegar,  Alkalised,  57. 

Artificial,  181,  191. 

bacteria,  31. 

-  beer,  8,  12. 
Cider,  184. 

Commission,  9,  13. 

—  Date,  189. 

-  Distilled,  136. 

eel,  122. 

fields,  98. 


INDEX. 


201 


Vinegar  fly,  128. 

—  Malt,  139,  179. 

—  manufacturers,  111. 
—  mite,  126. 

plant,  8,  54. 

Proof,  12,  14,  193,  194. 

Radical,  16,  57,  60. 

-  stills,  13,  135. 

Wine,  183,  186. 

Virgin  Island  vinegar  duties,  194. 


W 

Wagenmann's  graduator,  113. 

Whey  vinegar,  183. 

White  wine  vinegar,  136,  188. 


Wine  vinegar,  Composition  of,  183. 
—  Distilled,  183. 

Manufacture  of,  100. 

White,  136,  188. 


Wood  acid,  65. 
vinegar,  190. 


Yeasts  for  vinegar  brewing,  93. 


Zooglceal  condition  of  bacteria,  34. 


BK1L  AND  BAIN,  LIMITED,  PRINTERS,  GLASGOW 


14 


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