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The manufacture of
condensed milk, dried milk, cheese, and butter constitutes a series of
very important dairy industries. A full discussion and description of
these industries would be entirely outside the scope of this book. In
the following pages only that material is taken up which will be of most
interest and value to those desiring to preserve moderate amounts of
butter or who desire to make a small amount of cheese or who wish to
pasteurize milk in a small way. No attempt or claim is made to give a
description of commercial installations or practices.
108. Sterilization and
Pasteurization of Milk.
(a) Sterilization.
Enormous quantities of canned milk are used. Commercial factories
concentrate milk before canning and sterilization. This must be done in
a vacuum evaporator and cannot be carried out on a small scale. Milk may
be sterilized in sealed cans under steam pressure at ten pounds'
pressure for forty minutes or for one hour at 212 F. on each of three
successive days. Milk is exceedingly difficult to sterilize because of
the spore-bearing bacteria present. There is, however, very little need
of sterilizing milk in the household because it is usually not necessary
to keep it more than two or three days. Pasteurization is, however,
useful.
(b) Pasteurization of
Milk in the Household. Milk heated to 140º to 160° F. will keep much
longer than unheated milk. Heating to this temperature kills many of the
bacteria and so weakens those not killed that their growth is very much
slowed up.
Pasteurization may be
accomplished in bottles or in open pots. If carried out in bottles the
bottles should be scalded before filling. The filled bottles should be
sealed with sterilized corks. They may be heated in a pot of water with
bottles completely immersed until the water reaches 150º F. Maintain at
this temperature for twenty minutes. Remove and cool. A thermometer must
be inserted in the water to test the temperature.
The milk may also be
pasteurized by heating in a pot to 145° F. at which temperature it is
maintained for twenty-five minutes. A double boiler is best. Pour into
scalded jars or bottles. For practical purposes milk may be pasteurized
by heating in a pot to the simmering point or by "scalding "; that is,
heating to boiling. This is often necessary for the keeping of milk in
hot weather.
Pasteurized milk will
keep considerably longer than the unpasteurized, and will not contain
living typhoid or tuberculosis bacteria. Where there is any suspicion
that milk may be infected with disease organisms it should be
pasteurized; or if a thermometer is not available it should be heated to
boiling ("scalded ") before use.
109. Storage of Butter.
Butter may be kept very satisfactorily in cold storage, but this is
rarely available on the farm. The most practical method for farm use is
preservation by salting. Butter should be kept cool, excluded from the
air and away from the light. The spoiling of butter is brought about by
the formation of fatty acids from the butter fat and the decomposition
of the proteins and sugar in the buttermilk left in the butter. These
changes are largely bacterial in nature, although partly a simple
chemical change. Exclusion of air lessens the tendency for decomposition
by bacteria.
Preservation by salt may
be accomplished by adding from one-half to one pound of salt to each ten
pounds of butter. The salt is worked in thoroughly. The butter is packed
tightly in crocks and covered with salt.
Butter may also be
preserved by adding one-fourth to one half a pound of salt to each ten
pounds of butter and then storing the salt in a saturated brine (three
and one- half pounds of salt per gallon of water). This is the usual
household method. Such butter should be "freshened" by working in cold
water before use.
Butter contains casein
and buttermilk which tend to decompose. These can be removed by heating
the butter in boiling water a short time. The casein is coagulated and
falls to the bottom of the pot. The melted fat may be skimmed or poured
off without mixing any water with it. It is then poured in dry jars,
allowed to cool, and is sealed with paraffin. The butter is stored until
it is to be used and keeps well in this form. It must be salted before
it is used.
110. Cheese.
(a) "Cottage" Cheese. The
only cheese that may be made satisfactorily without special experience
and training is "cottage" cheese or "schmier kase." Formerly this
product was made only in the home. In recent years, however, it has been
made in large quantities for sale in delicatessens, restaurants, and
cafeterias.
Skim milk is ordinarily
used. It must be clean and of good quality. The first step is the
formation of the curd. This is ordinarily accomplished by permitting the
milk to sour naturally or by addition of a starter of lactic acid
bacteria. It may also be accomplished by the addition of rennet, as in
the making of hard cheese, but this produces rather a tough curd.
Seventy degrees Fahrenheit is considered the best temperature for
souring of the milk.
The curdled milk must
next be heated to coagulate the curd. This should not be carried out at
too high a temperature, or the curd will be tough and dry. The milk
should be heated slowly to about 100º F., i. e., blood temperature or a
little higher and kept at this temperature until the curd seems firm and
the whey clear. About half an hour's heating at this temperature will be
sufficient.
The Curd is then drained
through a cheesecloth for several hours. It is then broken up with a
wooden potato masher or with the hand. About one ounce (one
tablespoonful) of salt is added to each five pounds of curd. Other
flavorings, such as finely chopped pimento, or black pepper, or various
spices may also be added. "Pimento" cottage cheese is especially popular
in California. If a rich flavor is desired, cream or melted butter is
added and worked into the cheese.
Cottage cheese must be
used within three or four days. after it is made and is best when fresh.
It does not ripen and improve with age in the way that other cheese
does.
(b) Cheddar Cheese. This
is the most common type of American cheese. It is made from whole milk.
It cannot be made very successfully without considerable experience.
The first step is the
souring of the milk to .2% acid. This is done by the addition of a
starter of lactic bacteria and must be carefully watched by a chemical
determination of the acid.
Rennet is then added.
This is a substance obtained from the lining of calves' stomachs. It may
be purchased also under the name of junket tablets. Rennet coagulates or
curdles the casein. The curd is cut into cubes and left until the acid
reaches 1%. It is then salted, pressed, and left to ripen.
The ripening process is a
very complex one brought about by bacterial and enzyme action. Lactic
acid is formed from the milk sugar left in the curd; the casein or curd
is softened and partially decomposed and the butter fat undergoes
partial decomposition. Most of these changes are brought about by
bacteria occurring in the milk.
(c) Other Types of
Cheese. There are numerous other types of cheese. Space will not permit
their discussion here. Bulletin 146 of the Bureau of Animal Industry of
the United States Department of Agriculture gives good descriptions of
the various types. This bulletin may be obtained free of charge by
writing to the United States Department of Agriculture, Washington, D.
C. It is not recommended that the making of cheese (except cottage
cheese) be undertaken on the farm unless in a small experimental way and
with the personal advice and supervision of some one experienced in
cheese making. Recipes for cottage cheese and gouda cheese will be found
in Part III. |
