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UNITED STATES DEPARTMENT OF AGRICULTURE

Contribution from the Bureau of Chemistry
CARL L. ALSBERG, Chief

Washington, D. C. vV March 9, 1918

THE COMMERCIAL FREEZING AND STORING OF
7 FISH. _

By Ernest D. Cuark, Investigator in Fish and Fish Products, and Lioyp H.
Autmy, Assistant Chemist, Food Research Laboratory, prepared under the
direction of M. E. PENNINGTON, Chief, Food Research Laboratory.

CONTENTS.
Page. Page.
Freezing a means ofconserving the fish supply. 1 | Cold storage of fish........................---- 5
Preparavionorishess ses ee eee koe ee 2 Packing fish for storage..........-......... 6
Location: of freezers: ces of oc2. 8c ejoi. ee eee 3 WR gIAZING Ney eh ae ee sates okeera fe sels 6
(CUGVTOTES) Nie A ANE eae i i ae ee 3 Period jof storages cc oocide ssieieos we basses 7
ECOZINGMIST Seema ee fw PR ce nN FA IN 3 | Food value of frozen fish.....................-- 7
Freezing in ice or brine...................- 4 |. Handling of frozen fish after storage........... 8
(CUEVATIR As OS sees: ioe oti ge Oe Bea ASIN SUMMAL Yrs a cis cates Scie sie elaine tere eeioeee Se eile 9

FREEZING AS A MEANS OF CONSERVING THE FISH SUPPLY.

‘But for the fact that fish can be frozen and held in storage for
months without important change in food value or flavor vast quan-
tities of fish would go to waste, and this valuable nitrogenous food
and substitute for meat would be scarce or even unobtainable, except
in the smoked, salted, or canned form, during a large part of the
year. The additional fact that fish properly frozen and inclosed in
a protective glaze of clear ice may be shipped long distances without
deterioration permits many inland communities to obtain in the
winter tavorite varieties taken in distant waters. Without such
conservation bluefish would be on the market for only a few weeks,
and then mostly in the vicinity of certain waters; salmon, unless
canned or smoked, would be unknown in many sections; there would
be no country-wide interchange of halibut, pike, mackerel, smelts,
and other popular fish; and during the winter, when storms prevent
fishing and schools of fish migrate to deep water or southward, fish
of many varieties would be a costly delicacy instead of occupying
their matter-of-fact place on the table.

32658°—18—Bull. 685 —1

2 BULLETIN 635, U. S. DEPARTMENT OF AGRICULTURE.

The commercial supply of fish depends on weather conditions and
on the brief periods during which certain fish appear at banks or in
rivers to feed or to spawn. Much of the fish crop, therefore, is as
strictly seasonal as are the harvests of most of the perishable land
crops. During certain seasons fish are landed in quantities far in
excess of immediate needs, and, without effective conservation, these
vast temporary surpluses would go to waste. The importance ot
saving the surplus of spring, summer, and fall catches for later use
was appreciated long before conservation by freezing became known.
Each fishing season large quantities were saved, as they still are, by
canning, smoking, salting, and pickling. Freezing and storage, how-
ever, has the advantage over these other methods, in that it does not
alter the flavor or appearance of fish, and therefore makes available
months later, in almost the natural condition, the spring or summer
catches of seine or hook.

The fish-freezing plants (Pl. I, fig. 1) located at many points on
our coasts and the Great Lakes, and constituting an important indus-
try, are becoming increasingly useful as sources of nitrogenous food
to make up the deficiencies in the meat supply. Their work is true
food conservation. Harvests of fish, unlike land crops, add to rather
than take from the fertility of our soils. Meat represents the con-
version by animals of grain or other foodstuffs into another form of
food. Fish, however, represent the conversion of valueless aquatic
vegetation or animal material into human food, and, had merely for
the labor of harvesting, they are a net gain in the food supply.

PREPARATION OF FISH.

To produce frozen fish which after several months of storage will
be practically equal in food value and flavor to freshly caught fish,
it is essential that they be placed in the freezing rooms as soon as
possible after they leave the water. The fish should be handled as
little as possible, for any bruising, breaking of the skins, or damage
to fins either lessens their keeping quality or lowers the attractiveness
of the fish at market. Under no circumstances should fish be allowed
to become warm from the time they are caught until they are frozen.
Very slight exposure to warmth causes changes in their flesh which
no amount of freezing will remove.

The ideal method of freezing fish is that employed in winter in
Canada and other very cold sections (PI. I, fig. 2), where fish caught
through the ice or on the edge of the ocean are allowed to freeze natu-
rally as they leave the water. Such fish from our northern lakes,
and others, like the smelt from Nova Scotia and New Brunswick,
begin to freeze while they are still flopping on the ice or in the snow.
These frozen fish, which commonly have twisted bodies, due to being
frozen almost instantaneously while still alive, are known on the

COMMERCIAL FREEZING AND STORING OF FISH. 3

market as “ winter caught” or “naturally frozen” stock, and, when
the handling subsequent to the quick freezing is such that thawing
does not occur before the market is reached, they usually command
a premium because of their very fine flavor. While those who freeze
fish by artificial means rarely would be able to have fish delivered
alive to their plants, owners of freezers should make every effort to
have their fish delivered in prime condition.

LOCATION OF FREEZERS.

Fish freezers, therefore, are best located near those fishing grounds
which yield a regular supply of perfectly fresh fish (Pl. II, fig. 1).
If the plant is distant from the fishing ground, or if the fish can
not be delivered while still cold and within three or four hours after
they are taken from the water, the owner should demand that the
fishermen carry in the holds of their boats cracked ice for the proper
storing of the fish as they are taken. To avoid extra handling the
plant should be located near the water’s edge, and, if feasible, pro-
vided with mechanical conveyors which carry fish directly from the
boats to the cleaning tanks (PI. II, fig. 2).

CLEANING FISH.

Fish as they are received in the plant must be washed free from
all dirt and slime in clean, cold, running water conveniently pro-
vided in long tanks. Whether the fish should be “gutted” before
freezing depends upon their size and kind, and also, to some extent,
upon the market to be supped. New York and Boston, for example,
prefer salmon frozen in the “round”; other sections require that
the entrails be removed before freezing. In the case of bluefish and
other larger fish which are heavy feeders or which eat freely of
animal material, gutting before freezing seems desirable. This is
true also of fish which contain much oil, especially in the liver. Fish
containing much partly digested feed in the stomach or having much
oil in the flesh, deteriorate more quickly than do empty or lean
varieties. Gutting of smaller fish, such as butterfish, small mackerel,
small weakfish, and bass, is impracticable. These fish commonly
are frozen in their natural state in pans containing about 40 pounds
(Pl. III, fig. 1). Larger fish, like halibut and salmon, usually are
not placed in pans but are washed and frozen separately, especially
on the Pacific coast, where the fish frozen are largely of these two
varieties, although some black cod or “sablefish” are handled.

FREEZING FISH.

In the most successful establishments the panned fish are placed
directly on the refrigerator pipes in the “sharp freezer” room the
temperature of which varies from —5° to —15° F. (Pl. ITI, fig. 2).

4 BULLETIN 635, U. S. DEPARTMENT OF AGRICULTURE,

These pipes are usually direct expansion pipes from the ammonia
refrigerating plant. They are so arranged that they make a series
of shelves one above the other, each consisting of numerous pipes.
Passageways are left between each set of shelves for the convenient
handling of trucks. Some plants have installed mechanical con-
veyors to facilitate carrying the fish to and from the fish-freezing
rooms.

The operators remove the frozen fish from the pan by pouring a
little cold water on the outside of the pan, which causes sufficient
melting to allow the frozen fish to slip out in a block. Fish which
are to be frozen separately are laid on thin metal sheets resting on
the cold pipes, or they are suspended in the air from iron rods or
hooks. Fish, single or panned, freeze thoroughly in from 12 to 30
hours,. according to their size and the temperature of the freezing

room.
FREEZING IN ICE OR IN BRINE.

The older method of freezing fish by packing them in covered pans
which then are buried in ice and salt still is practiced in some dis-
tricts. This plan is not adapted to freezing fish rapidly on a large
scale and does not lend itself to accurate control of temperature.
Methods of freezing fish in saturated salt brine, cooled to low tem-

peratures by freezing coils, recently have been patented. The salt

in brine chilled almost to its freezing point apparently does not pene-
trate into the fish to any great extent, and freezing is much more
rapid than in air. These processes have great merit from the theo-
retical point of view, and appear to be adapted to commercial condi-

tions, but as yet they have not been adopted by the trade in this
country.
GLAZING.

Glazing, an important step in the freezing of fish, is designed to
incase each fish or each block of frozen fish with an air-tight pro-
tective envelope or cover of clear ice. Unless glazed, the skins of
frozen fish are liable to turn white and the fish themselves will
shrivel because of loss of moisture which takes place even at freezing
temperatures. Noses and fins of frozen fish, unless protected by
glazing, are the first points to show the effect of loss of moisture.
Glazing also helps to prevent the eyes of the fish from becoming
opaque and shrunken and to obviate deterioration which makes the
gills, which normally are bright red, darker and brownish. Glazing
prevents the evaporation of the moisture from the flesh of the fish,
prevents the entrance of air which tends to make the fish oils dete-
riorate, provides an ice surface upon which molds and fungi can not
grow, and finally helps to protect the fish from mechanical injuries
which mar its appearance.

————— ee ee

COMMERCIAL FREEZING AND STORING OF FISH. 5

For glazing, the frozen fish are taken to the glazing room, which
is held at a temperature of 20° to 25° F., or just cold enough to
cause thin layers of cold water to freeze rapidly. The glazers
slide the frozen cakes of panned fish, or the separately frozen fish,
quickly through a trough of clean, clear water held just above the
freezing point. (PI. IV, fig. 1.) This water covers the product
with a thin film which in the cold air freezes instantly into a crystal-
clear glaze of ice like a transparent varnish. Unless the water is
changed frequently, however, it is apt to collect oils or other material
from the fish which will prevent the glaze from forming evenly on
all parts of the fish or give the ice coating a cloudy appearance.

Fish are passed through the water from three to five times until the
several coats of glaze form a sufficiently heavy and permanent ice
envelope covering the entire surface. Even before glazing the blocks
of frozen fish in the pans have become solid cakes, the fish being
held together by the freezing of the thin layer of water between them,
and the glazing still further cements them to each other. Glazing
of fish adds about 5 per cent to their weight, although this varies
with the size of the fish and the number of glazings. To expedite
the glazing of separately frozen fish, operators on the Pacific coast
place the fish on small platforms, which are lowered by a winch into
a tank of water and raised again. This process is repeated until
the glaze which hermetically seals the fish and prevents deterioration
is of the proper thickness.

COLD STORAGE OF FISH.

The glazed fish are taken immediately to the cold-storage rooms
to be kept until sent to market. (PI. IV, fig. 2.) These are rooms
with coils of ammonia or brine pipes attached to walls and ceilings,
but not arranged in the form of shelves, as in the freezing rooms.

The subject of the proper temperature for the long storage of
frozen fish has been much discussed. Investigation seems to prove
that ordinarily the most economical and safest temperature for hold-
ing fish is at any point from zero to 10° F., with as little variation
in temperature as possible. Some plants, especially small establish-
ments in isolated localities, try to keep their frozen fish at from —5°
to +5° F., because fish held at these temperatures would not spoil
quickly should an accident to the refrigerating machinery interrupt
artificial refrigeration for a day or two.

In determining the temperature of the storage room, operators are
cautioned not to be guided by floor temperatures alone, but to place
thermometers so that readings can be taken at the top of the room,
to which the warmer air naturally rises, affecting the uppermost
fish. It is suggested that if the owner can not provide two or more
thermometers he hang a thermometer from a pulley on the ceiling

32658°—18—Bull. 6352.

6 BULLETIN 635, U. S. DEPARTMENT OF AGRICULTURE.

so that he can take readings of the air at various heights, especially
at and above the upper fish. Every operator, of course, under-
stands the importance of keeping doors to cold storages closed, par-
ticularly when they open into outside air or into halls warmer than
the storage rooms themselves.

PACKING FISH FOR STORAGE.

Before storage, frozen fish, especially on the Atlantic coast, com-
monly are placed in boxes lined with heavy Manila paper, which
makes a better-looking package and gives additional protection.
These boxes simplify the handling and shipping of fish, and also
enable warehousemen to comply with any local laws which require
that the date of entering the storage be stamped on the packages.
Boxing the frozen fish before storage, by lessening the free circula-
tion of air among the fish, helps also to prevent evaporation of the
ice glaze, for ice evaporates even at freezing temperatures, as is
evidenced by the gradual shrinking of a block of ice outdoors, even
in zero weather. Boxed fish which have received from three to five
glazings usually keep from three to five months without losing their
glaze, or much longer than unboxed fish exposed to the air.

Four or five cakes of the panned fish, or 120 to 160 pounds, com-
monly are packed in one box, whose length and width are just large
enough to take these cakes from the pans. Separately frozen fish,
such as halibut, salmon, and other large fish, generally are first
wrapped in a fish-wrapping paper, usually a vegetable parchment
paper, and packed carefully in boxes hned with Manila paper. On
the Pacific coast longer narrow boxes are used for packing halibut
and salmon. While under some conditions the cheaper sorts of fish
are stored in bulk, either in bins or in stacks, the boxed fish keep their
glaze better and are less liable to damage from handling.

REGLAZING.

Because the glaze gradually evaporates, it is necessary, 1f the fish
are to be kept in storage for a long time, to remove them from their
boxes and reglaze them at intervals of from three to four months.
Reglazing of fish stacked or kept in bins is somewhat more difficult.
A method occasionally followed in reglazing such fish is to use a
hose with a special spray nozzle, similar to that employed in white-
washing. The nozzle plays a finely-cdivided stream of clean water
on the piles of frozen fish, and this, freezing rapidly, reglazes them
more or less satisfactorily. The glaze naturally evaporates most

rapidly from the outer surface of the pile most exposed to air, and_

these parts fortunately are most accessible to the reglazing spray.

y

Bul. 635, U. S. Dept. of Agriculture. PLATE lI.

Fia. 1.—THE LARGEST FISH FREEZER IN THE UNITED STATES.
The State of Massachusetts built this freezer, which has a capacity of 15,000,000 pounds of
frozen fish.
ie 4

FIG. 2.—WINTER-CAUGHT, OR NATURALLY FROZEN, FISH.

Bul. 635, U. S. Dept. of Agriculture. PLATE II

Fic. 2.—CONVEYOR CARRYING FISH FROM ICE HOLD OF BOAT TO FREEZER.

5

Bul. 635, U. S. Dept. of Agriculture. PLATE III.

FIG. 1.—PANNING FISH, PREVIOUSLY WASHED IN LONG TANK BESIDE WHICH THE
MEN ARE STANDING.

Fic. 2.—SHARP FREEZER ROOM.

Bul. 635, U. S. Dept. of Agriculture.

PLATE IV.

FIG. 1.—PUTTING FISH IN ICE ENVELOPES.

FiG. 2.—COLD-STORAGE ROOM.

PILES OF FROZEN
SHIPMENT.

HALIBUT READY FOR BOXING AND

te

COMMERCIAL FREEZING AND STORING OF FISH. 7

PERIOD OF STORAGE.

The average period of storage for fish, as shown by investigation
and statistics, is approximately only eight months. Much frozen fish,
however, is sold within a few months after it is stored, and only
rarely are batches of fish held as long as twelve months. Careful
analysis of fish properly stored for such periods fails to indicate
any important change in the food value of the fish, or to reveal any
noticeable alteration in the flavor. To study in a practical way the
effect of freezing storage on flavor, one of the writers’ arranged a
test with a large group of people who were unaware that they were
being used for subjects. These people were served a half portion of
fresh fish (mackerel) and a half portion of the same species of fish
properly frozen and stored for nine months. The average individual
was unable to distinguish between the fresh fish and the frozen fish,
and a number expressed a preference for the frozen lot.

In an effort to determine the natural storage limits for frozen
fish, the department’s investigators recently held frozen fish for
twenty-seven months under close observation in a Government ex-
perimental freezer. Elaborate analyses of the fish at various time
~ intervals and at the end of this period failed to show changes which
rendered them at all unsuitable for food, or to indicate any impor-
tant differences in chemical composition between these fish and fresh
fish or fish stored for shorter periods. The actual period for which
any batch of fish will be held in storage depends, of course, largely
upon the market conditions. Only under very unusual circumstances
are frozen fish held for more than one year, because the season of
fresh fish of any particular species will recur in ten or twelve months,
and frozen fish bring lower prices than fresh fish. Frozen fish must
be marketed before fresh fish again become plentiful on the market.
Other deterrents against holding fish for any great length of time
are the cost of refrigeration, labor, and reglazing, insurance during ~
storage, interest on capital, and other factors which promote with-
drawal from storage as soon as a favorable market can be obtained.
The legal limit on the storage of fish in several States varies from
nine to twelve months, although in certain States extensions can be
secured upon application to the proper authorities. Observations
show, however, that only under very abnormal conditions and in
unusual seasons is there either any necessity for or commercial ad-
vantage in holding fish longer than nine or ten months.

FOOD VALUE OF FROZEN FISH.

- Fresh fish, properly frozen, glazed, and held at low temperatures
for nine months or a year show no important changes in composi-
tion to the food chemist or bacteriologist. No lessening of palata-

1From unpublished investigations of L. H. Almy.

8 BULLETIN 635, U. S. DEPARTMENT OF AGRICULTURE.

bility noticeable to the average housewife occurs. This is to be
expected, as freezing, unlike most other preservative measures, takes
nothing from the fish and adds nothing to it except a thin outer
covering of ice which soon melts upon thawing the fish for con-
sumption. The low temperatures at which the flesh is held in
storage are well designed to prevent chemical or other changes over
a number of months. Freezing, however, merely holds the fish in
the condition in which it entered the freezing room. Cold can not
restore freshness to old fish nor overcome deterioration from care-
less handling or exposure to warmth. The freezer can deliver fish
practically as good as but not better than that which it receives.

To determine the behavior of fish under storage the Bureau of
Chemistry held fish for the excessively long period of twenty-seven
months in cold storage under its control. At different times sample
lots of fish were withdrawn and analyzed. These studies showed no
significant difference in composition between the frozen fish and
fresh fish of the same species. Of special interest is the fact that no
loss of those nitrogenous constituents which give to fish its chief food
value was noted.

According to these analyses, the process of freezing and storing
causes no appreciable chemical change in those constituents upon
which the food values are usually calculated, even when the storage
is prolonged for greater periods than are necessary or profitable in
commercial practice. In some cases the chemists were able to detect
after storage very slight changes in the percentage of ammonia and
certain other constituents. These changes, however, affect in no
way the food value of the fish, and, in fact, the differences often
were not as great in the same lot of fish before and after storage as
they were between two individuals of the same species when analyzed
in the fresh condition.

HANDLING OF FROZEN FISH AFTER STORAGE.

When frozen fish have thawed they are as perishable as fresh fish,
and should be consumed as quickly as possible. Even partial thaw-
ing lessens greatly the perfect protection of glazing and hard freez-
ing. Retailers, therefore, should make every effort to have their
frozen fish reach them hard frozen with glaze unimpaired. After
the fish reach them the retailers should make very effort to keep
them hard frozen and glazed until they are actually sold. This
best can be accomplished by ordering frequently and not in excess
of immediate sale. Customers should be encouraged to buy fish in
the hard-frozen state, either to be thawed out to order by the retailer
or, even better, delivered to the housewife hard frozen. She then
should place them in a covered utensil in the refrigerator, or other
cold place, and allow them to thaw gradually. Fish never should

COMMERCIAL FREEZING AND STORING OF FISH. 9

be thawed by exposure to heat or by soaking in either cold or warm
water. Such rapid thawing lessens their food value, and tends to
dissolve out flavors essential to their palatability.

SUMMARY.

Freezing and freezer storage will hold fish for many months in
the condition in which they were received, but will not repair dete-
rioration due to previous heating or mishandling.

Freezers should accept only fish that are in prime condition.
Unless delivered within three or four hours after being taken from
the water, fish should be kept under refrigeration in the boats.

Rapid freezing at as low temperatures as possible is necessary
in many plants in order to insure a good product and to handle
receipts as they arrive.

Glazing by inclosing the fish in an envelope of ice prevents loss
of moisture, protects the fish from molds and bacteria, and makes
them less subject to mechanical injury. Fish to be stored for more
than three to five months should be reglazed occasionally, as in time
the glaze evaporates, even at low temperatures.

The most economical temperature for storing fish is probably at
some constant temperature between 0° and +10° F., although some
freezers hold that lower temperatures tend to delay evaporation of
the glaze.

Boxing fish before storage helps to prevent loss of glaze, and pro-
tects the product from mechanical injury.

Properly frozen fish reach the retailer in excellent condition. He
should keep them hard frozen until they are sold. The practice
of thawing fish by warming or in water greatly lessens their food
value and flavor.

Chemical analyses show no significant changes in fish held twenty-
seven months, or for a period much longer than would be necessary
or profitable in storing fish commercially.

PUBLICATIONS OF THE U. S. DEPARTMENT OF AGRICULTURE
RELATING TO REFRIGERATION.

PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION BY THE DEPARTMENT.

Study of Preparation of Frozen and Dried Eggs in Producing Section. (De-
partment Bulletin No. 224.)

Shrimp, Handling, Transportation, and Uses. (Department Bulletin No. 538.)

Studies of Poultry from Farm to Consumer. (Chemistry Circular No. 64.)

Practical Suggestions for Preparation of Frozen and Dried Eggs, Statement
Based on Investigation Made in Producing Section During Summer of 1911.
(Chemistry Circular No. 98.)

Supplementing our Meat Supply with Fish. (Separate 623 from Yearbook
1913.)

PUBLICATIONS FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, GOVERN-
MENT PRINTING OFFICE, WASHINGTON, D. C.

Changes in Fresh Beef During Cold-Storage, Above Freezing. (Department
Bulletin No. 483.) Price, 10 cents.

Preliminary Study of Effects of Cold-Storage on Eggs, Quuil, and Chickens.
(Chemistry Bulletin No. 115.) Price, 40 cents.

Bacteriological Study of Shell, Frozen, and Desicgated Eggs, Made Under Labo-
ratory Conditions at Washington, D. C. (Chemistry Bulletin No. 158.)
Price, 10 cents.

Handling of Dressed Poultry a Dhoukdnd Miles from Market (Separate 591
from Yearbook 1912.) Price, 15 cents.

Shipping Fish Three Thousand Miles to Market. (Separate 665 from Yearbook
1915.) Price,-5 cents.

10

ADDITIONAL COPIES

OF THIS PUBLICATION MAY BE PROCURED FROM
THE SUPERINTENDENT OF DOCUMENTS
GOVERNMENT PRINTING OFFICE
WASHINGTON, D. C.

AT
«CENTS PER COPY

V

WASHINGTON : GOVERNMENT PRINTING OFFICE : 1918

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