DAIRY PRODUCTS

227

ripening ferments. It contains, in the water free substance, not
less than 50 per cent of fat.

Manufacture.—The action of the enzyme rennin is to change
the casein, by hydrolysis, into albumoses and peptone and soluble
paracasein. The calcium salts present in solution in the* milk
serum unite with the soluble paracasein to form an insoluble
curd. The curd carries down not only the fat but also the greater
part of the microorganisms contained in the milk. If these
organisms are of a desirable kind they will produce a homo-
geneous curd and good cheese, otherwise a spongy curd and a
cheese of poor consistency will be the result.

The table below gives the average composition of certain
samples of four kinds of cheese,

TABLE XXL—COMPOSITION OP CHEESE

Primary
Secondary

Kind of cheese
Water
Fat
Ash
Proteins
products of
products of

ripening
ripening

American "Cheddar"
34.2
33.7
3.8
25.2

.

Roquefort . . . .
31.2
33 ?,
6.0
27.6

Swiss ...........
33.0
30 ?,
5 3
25.4
2.7
3.1

Gervais
44 8
36 7
2 9
12 7
1 9
0 8

Determination of Water.—Place about 15 gm of clean white sand in a
flat aluminium dish, dry at 100° and weigh. Add about 3 gm of cheese
and reweigh, quickly. More sand is needed if the cheese is very rich in fat.
The mixture is then dried at 100° to constant weight and the per cent loss in
weight calculated as moisture.

Determination of Ash and Salt.—Ignite, cool and weigh a covered porce-
lain crucible. Add about 15 gm of cheese, cover and reweigh. Uncover the
crucible and drive off most of the moisture and volatile matter by carefully
heating over a small flame. Place the uncovered crucible in a muffle furnace
which is held at about 600° and through which air may circulate. Continue
the heating until all carbon is burned. Cool in a desiccator and weigh.
Calculate the per cent of ash.

After weighing the ash, add water, dilute to 250 cc in a volumetric flask
and mix. Either 50 or 100 cc of this solution is taken for the chlorine
determination as directed on page 223. Calculate as sodium chloride. The
residue insoluble in water may be dissolved in a small amount of dilute
hydrochloric acid, diluted to 250 cc and calcium and phosphorus determined
in aliquot parts of this solution, if desired.

ij:
li