THE PREPARATION AND PRESERVATION OF FOOD.
OBJECTS OF COOKING.—Food may be taken in its crude condition, as
directly derived from the animal or vegetable world, or after it has
undergone a preparatory process of cooking. Man is the only animal
who cooks his food. Many foods, in the uncooked condition are almost
entirely incapable of digestion by him—such as the proteid and
farinaceous materials contained in the seeds of cereal and leguminous
plants. But cooking, as a preparatory help to the digestion of food,
is not equally required by all foods. Thus, fruit is commonly taken
uncooked, and does not undergo any important alteration on cooking.
Salads are taken uncooked, but not for their nutritive properties so
much as for a relish to other foods, and for their quasi-medicinal
properties. Milk, again, may be taken cooked or uncooked. The oyster
is the only animal which is eaten habitually, and by preference, in
the uncooked condition; and there is a physiological reason for this
universal custom. The large fawn-coloured liver, which constitutes
the delicacy of the oyster, is little else than glycogen, associated
with its appropriate ferment diastase, so that the oyster is almost
self-digestive. When cooked, the ferment is destroyed, and digestion of
the oyster becomes more difficult.
Cooking is intended—1. _To make the food softer_, and in part to
mechanically disintegrate it, thus rendering it more easily masticated
and digested. In fact, cooking, in the best sense, is an artificial
help to digestion; and digestion may well be said to commence in the
kitchen.
2. _To produce certain chemical changes._ Thus, starch is partially
converted into dextrine; gelatin is formed from connective tissue, etc.
3. _To destroy any noxious parasites_ present in the food, or obviate
any ill effects from _putrefactive changes_. Diseased meat chiefly
produces bad effects when imperfectly cooked.
4. _To make the food more pleasant_ to the eye and agreeable to the
palate. The improved savour in cooked meat, for instance, has a very
appetising effect, and consequently makes digestion easier.
THE COOKING OF FLESH.—1. =Roasting= is, perhaps, the most perfect way
of cooking meat. It exalts its flavour more than any other method. In
roasting, place the meat at first sufficiently near a brisk fire, so
that the albumin on its surface may be readily coagulated, and the
juices retained in the interior of the joint. After about fifteen
minutes, the joint ought to be removed somewhat further from the fire,
and allowed to cook slowly. Frequent basting is desirable to obtain a
good result. Brown meats, such as beef, mutton, and goose, require a
quarter of an hour per pound weight; veal and pork require about ten
minutes additional, to ensure the absence of redness. White-fleshed
birds require a somewhat shorter time. The time required in roasting
will be a little more if the joint is large, or the fire not very
clear. To ascertain if the meat is sufficiently cooked, press the
fleshy part; if it remains depressed, it is done; if not done, it
retains its elasticity. At the first incision, gravy should flow out of
a reddish colour.
_The changes undergone_ during roasting are, that the connective
tissues uniting the muscular fibres is converted by the gradual heat
into gelatin, which is soluble and easily digested; the muscular
fibres, consequently, become more separable, and the myosin of which
they consist is rendered more digestible. The fat is partly melted
out of its fat cells, and partly combines with the alkali from the
blood-serum. Empyreumatic oils (_i.e._ fat partially burnt), developed
by charring of the surface of the joint, are carried off when it is
roasted in front of the fire; and so, to a large extent, is acrolein.
Acrolein (C₃H₄O) is always produced by the destructive distillation of
neutral fats containing glycerine, and is the cause of the intolerably
pungent odour accompanying the process. Osmazome, a peculiar extractive
matter, on which the flavour and odour of meat depend, is developed
better by roasting than by any other method of cooking.
It is useful to remember, in buying beef or mutton, that 20 per cent.
must be allowed for bone and 20 to 30 per cent. for the loss during
cooking.
The following figures are by Johnston:
IN ROASTING. IN BAKING. IN BOILING.
4 lb. of mutton lose in weight 1 lb. 6 oz. 1 lb. 4 oz. 14 oz.
„ beef „ „ 1 lb. 5 oz. 1 lb. 3 oz. 1 lb.
Thus roasting is the least economical method of cooking. The chief
loss, however, is of water; the dripping and gravy are recoverable.
2. =Baking= of meat in a closed oven does not produce so agreeable a
result as roasting in front of an open fire. The oven ought always to
be very hot before the meat is put in, in order to rapidly coagulate
its surface. Baked meat may have an unpleasant flavour, owing to its
saturation with empyreumatic oils, which escape in open roasting. The
unpleasant flavour can be prevented by covering the meat with a layer
of some non-conducting material, as a pie-dish or a crust, no empyreuma
being then formed. Baked white of egg, as in the dish of fried ham and
eggs, is one of the most indigestible forms of albumin obtainable.
3. =Boiling= of meat requires the same time as roasting. If the flavour
and juices are to be retained, the joint ought first to be plunged into
soft boiling water, and then, after three minutes, allowed to stand
aside in water at 170° Fahr. The preliminary boiling forms a coating
of coagulated albumin over the joint. Where there is no thermometer
to guide the cooking—after the preliminary boiling for three to five
minutes, add three pints of cold water to each gallon of boiling water,
and retain at the same temperature for the rest of the process, _i.e._,
at about 170° Fahr. If the meat is boiled in an inner vessel surrounded
by water (water-bath), the temperature of the inner vessel does not
rise above 160°-170° F. Ordinary “simmering” means that the meat is
kept all the time at a temperature of 212° F. and is thus spoilt. The
boiling of an egg is an example of the same point. If an egg is kept in
water at a temperature of 170° F. for 10 to 15 minutes, its contents
form a tender jelly, while an egg kept in water at 212° F. for the same
length of time is hard and tough. An egg is more digestible when cooked
in water at 170° F. for 10 minutes than when boiled in water for 2½
minutes.
The use of soft water for cooking purposes is always advisable;
otherwise a longer period must be allowed. A preliminary boiling for
a few minutes renders hard water softer, and the addition of a little
carbonate of soda has a like effect.
When meat is inserted in water at a temperature below its boiling
point, the juices are gradually extracted, while the meat is left a
mass of indigestible fibres. A good soup is produced, but the meat is
almost valueless. In order that the soups and broths may be nutritious,
the less heat is employed in their preparation the better. If a soup is
strained to make it clear, much of the most valuable part is removed.
=Stewing= is a process intermediate between boiling and baking. It
possesses the great advantage over dry baking that no empyreumatic
gases are produced, and there is no charring. The temperature of the
stew-pan ought never to be above 180° Fahr.; at this heat the roughest
and coarsest kinds of meat are made tender. The only objection to
stewing is that the meat becomes saturated with fat and gravy, and is
too rich for weak stomachs. It is advisable to stew lean meats only.
=Hashing= is a process of stewing applied to meat which has been
previously cooked. The consequence of this double cooking, is that the
meat becomes tough and leathery. A modified hash in which the meat is
simply well warmed throughout is preferable.
=Frying=, unless carefully done, renders meat difficult of digestion,
each fibre becoming coated with fat. The art is to “fry lightly,” that
is, to burn quickly and evenly, so that no charring is produced. Two
methods of frying are described. In the first, the substance to be
fried, as an omelette or pancake, is placed with a little fat or oil
in a frying-pan. This is really a modified process of roasting, the
fat merely serving to prevent the object from adhering to the shallow
pan. In the second, the substance to be fried is immersed in fat; for
this purpose a frying kettle is required. Olive oil or good cotton
seed oil is best for use in the frying-kettle. Lard is a bad material
for frying; both it and butter are apt to burn unless heated slowly.
Dripping is a good substance for frying. The fat used must be heated
to from 350° to 390° F., and then the substance to be fried, _e.g._
a sole, plunged into it and left for two or three minutes. In this
process the substance of the sole is really being steamed by the steam
generated in the substance of the sole.
6. =Broiling and Grilling= are really processes of roasting applied to
small portions of meat. In grilling, it is important that the gridiron
should be hot before putting anything on it. An external coagulation of
albumin is produced, as in good roasting and boiling.
THE COOKING OF MIXED DISHES.—A few instances may be given of common
errors in preparing compound dishes. An egg in a custard, or just
coagulated in a poached egg, is a light and easily-digested food; baked
half an hour in a pudding, it is much less digestible; fried with ham,
it is almost as indigestible as leather. Spices, if mixed with a dish
before it is boiled, lose nearly all their flavouring power, while they
remain irritating. They ought to be added near the end of the cooking
process. A soup containing vegetables, as well as meat juices, should
be prepared in two parts. The vegetables require prolonged boiling;
gravy is spoilt by this. Similarly, the jam in a tartlet, if inserted
before baking, loses its proper fruity flavour; and oysters baked in a
beef-steak pie are indigestible.
THE COOKING OF VEGETABLE FOODS.—=Bread= is either vesiculated or
unvesiculated; the latter being what is called unleavened bread.
Vesiculation of bread has usually been produced by _fermentation_
of some of the sugar of the flour. The starch first becomes sugar
(dextrose) and then the growth of the yeast plant in the dough
splits this up into alcohol and carbonic acid gas. The carbonic acid
percolates the substance of the dough, rendering it porous. When it has
“risen” sufficiently, the dough is placed in the oven. The heat of the
latter kills the yeast plant, thus preventing any further fermentation,
but at the same time expands the carbonic acid gas in the bread,
rendering the latter still more porous, and drives off in a gaseous
condition the greater part of the alcohol produced by the previous
fermentation.
It is objected to this plan of making bread, that a little of the
sugar is wasted in producing alcohol and carbonic acid. To remedy
this, _another plan_ is sometimes adopted, as first proposed by _Dr.
Dauglish_. In it the dough is charged with carbonic acid dissolved in
water under considerable pressure. The gas escapes in the substance of
the dough, and on baking expands as in the ordinary method of making
bread. Bread made in this manner, is called “aerated bread.” Nevill’s
bread has a solution of carbonate of ammonia incorporated in the dough,
which is dissipated by heat, thus causing vesiculation of the bread.
On the continent, a mixture of hydrochloric acid and carbonate of soda
is commonly used, carbonic acid and common salt being formed in the
dough. Thus NaHCO₃ + HCl = NaCl + H₂O + CO₂. The hydrochloric acid
employed should be perfectly pure and free from arsenic. Baking powders
are also largely used for making cakes. “Self-raising” flour is flour
with which baking-powder has already been mixed. Most baking-powders
consist of a mixture of carbonate of soda and tartaric acid or
bitartrate of potash, diluted with starch. When wetted, carbonic acid
gas is evolved. A few contain alum, which is now an illegal material
for this purpose.
Ten pounds of flour ought to make thirteen to fourteen of bread.
The use of stale bread is much more economical than of newly-made
bread; besides this, it is more digestible. Newly-made bread is more
palatable than stale, but it is more cohesive, and does not crumble
into separate particles like stale bread. The consequence is, that it
is less digestible, being less easily penetrated by the saliva and
other digestive juices. The effect of _toasting_ is to render bread
more friable, and consequently more digestible. It ought, however, to
be thin and eaten soon after it is made; when thick and kept too long,
it becomes tough and leathery.
=Pastry= is less easily digested than ordinary bread. The lard or
dripping added renders it more flaky and less easily pulverised; and,
in addition, the fat coats over the starch cells; and thus the action
of the digestive juices on the pastry is impeded.
=Potatoes= ought to be boiled in their jackets, or steamed, to avoid
loss of nitrogenous material and salts. Moist heat causes the starch
granules to swell, and ultimately softens and bursts the cellulose
envelopes in which these are contained. Dry heat, as when potatoes
are baked, converts starch into a soluble form, and ultimately into
dextrine (= C₆H₁₀O₅), an intermediate stage towards the formation of
dextrose (_i.e._ glucose = C₆H₁₂O₆).
=Peas and Beans= ought to be boiled slowly and for a long time to
render them more digestible. If old, they ought to be soaked in cold
water for twenty-four hours, then crushed, and stewed. Hard water
must be avoided in the cooking of peas and beans as well as of other
vegetables, as the lime-salts form insoluble compounds with legumin.
=Green vegetables= require thorough and prolonged cooking. This renders
their tissues softer and more easily attacked in digestion. The members
of the cabbage tribe and carrots can hardly be boiled too long. Soft
water ought always to be used; this is one reason why steaming is
preferable. Before boiling, all vegetables should be well washed in
cold water. A little vinegar will remove any insects present.
COOKING APPARATUS.—The apparatus required in cooking may be divided
into kitchen utensils and cooking ranges.
To ensure good cooking, perfect cleanliness of all apparatus is
indispensable. The use of the frying-pan, gridiron, spit, and oven has
been sufficiently indicated under the description of the different
methods of cooking. The form of stove to be used for cooking meat is
gradually being settled against the old open stove. Although this
secures a somewhat more savoury joint than when meat is baked, it is
extravagant in working. The closed kitchener in which coal is employed
is less economical than a gas stove at the present price of gas, if the
latter is carefully used.
Various appliances for economising fuel have been devised, and at the
same time of allowing of the prolonged action of a moderate degree of
heat. These are usually constructed on the principle of an ordinary
bath, consisting of a double pan, with a layer of water between the
two compartments. Warren’s cooking-pot belongs to this type. The
Aladdin oven consists of an iron box with an opening above to let
off superfluous steam. This box is surrounded by another composed of
non-conducting material, while a lamp below furnishes the heat. Dr.
Atkinson has calculated that in an ordinary oven 2 lbs. of fuel must
be expended for every pound of food cooked, while in his Aladdin oven
2½ lbs. of fuel will cook 60 lbs. of food. Time is an important
element in cooking. Food is most thoroughly cooked and most digestible
when subjected to a temperature below that of boiling water for a
prolonged period.
THE PRESERVATION OF FOOD.—All organic foods tend rapidly to decompose
and putrefy. Putrefaction only occurs when a warm and moist substance
is exposed to the air. The problem of preserving any food, therefore,
may be solved (1) by keeping it at a very low temperature, (2) by
desiccating it, or (3) by boiling or steaming it so as to destroy any
microbes in the food which would otherwise start putrefaction, and then
fastening it in an air-tight case.
Milk is commonly preserved as condensed milk, and in this condition
is very valuable. A pure condensed milk is now supplied, prepared
without the addition of sugar or any antiseptic, but in which, as in
other condensed milks, all disease-producing or decomposition-producing
microbes have been destroyed during the process of concentration. Milk
may also be desiccated; in this condition it is difficult of digestion.
In addition to the household methods of preserving fruits, large
quantities of fruits—both moist and dry—are now imported, protected
by syrup or sugar, in sealed canisters; and they retain the original
flavour almost unchanged.
The preservation of meat is effected by—
1. =Drying.=—This must be done rapidly. It is a process which is best
applicable to fish, but has been applied also to beef. Dried Hamburg
beef is used for making sausages. Pemmican, largely used by Arctic
voyagers, consists of a mixture of meat and fat, dried and powdered
along with some spices; it is generally eaten with some kind of meal.
2. =Cold.=—Frozen meat now forms a very large part of the food of
the English people. If the meat has been frozen before rigor mortis
(rigidity after death) has commenced, it keeps well; if frozen later,
it rapidly decomposes after being thawed. Freezing arrests putrefaction
and tends to conceal its odour. Hence the bad condition of frozen fish
may not be detected until it is cooked. In cooking frozen meat, time
should be allowed for thawing to occur, before the meat is placed in
the oven. Much of the ill-founded prejudice against frozen meat arises
from inattention to this point. Frozen meat is equal in nutritive value
to and does not lose more in cooking than fresh meat.
3. =Salting= may be done with brine or saltpetre (nitrate of
potassium); the latter does not decolourize the meat like the former.
Salted meats have lost much of their nutritive material, in the
form of albumin and salts, and the remaining meat is harder and more
difficult of digestion than fresh meat.
4. =Immersion in antiseptic liquids= or gases, as sulphite of soda,
is objectionable, on account of the addition of extraneous, and not
altogether innocuous, salts. Boric acid powder is largely used for
sprinkling on meat, particularly rabbits, etc., and for preserving hams
and other meats. Its use is to be deprecated. All such meats should be
thoroughly washed with water, before being cooked.
Solutions of _boric acid and borax_ are frequently added to milk. Their
use is objectionable (_a_) because they tend to conceal incipient
decomposition, but do not prevent its possible evil effects, and (_b_)
because they enable the farmer to palm off dirty milk on the public.
Were the addition of preservatives to milk forbidden, the farmer could
perfectly well keep his milk sweet until it reached the town-consumer
by adopting strict measures of cleanliness, and by cooling his milk
before it leaves the farm. At the least it should be made obligatory on
the milk retailer to declare the presence of preservatives in milk sold
by him.
The presence of borax or boric acid can be detected by evaporating
the milk to dryness, incinerating and then moistening the ash with a
drop of strong sulphuric acid. If a little alcohol be now added, on
applying a light, a green flame indicates boric acid. Milk or cream
containing boric acid turns blue litmus paper red.
_Formalin_ is also sometimes used as a preservative for milk in very
weak solution.
Its presence can be determined by diluting the milk with water in a
test-tube, and running strong sulphuric acid down the side of the
tube, taking care to prevent mixing. At the junction of the acid and
diluted milk a violet ring is seen if formalin is present.
_Salicylic acid_ was formerly used as a milk preservative, but is now
seldom used except in beers. All these preservatives are objectionable
in milk, although their injurious action may be difficult to prove.
5. =Coating with fat or gelatine= has only succeeded in conjunction
with the exclusion of air. This process is especially applicable to
fishes, as tinned sardines. In a modified form, it is useful in coating
potted meats, etc.
6. =Heating and Air-tight Cases.=—Tinned meats prepared according
to this method are imported in large quantities. In the process of
preparation, the cases are packed with meat and filled up with gravy,
and then closed with a cover which is hermetically sealed, except at
one point. The case is then heated to 250° Fahr., in order to drive
out all air, and destroy any putrefactive germs present. The open
point is sealed while the gravy is still boiling, thus making the case
completely air-tight. Albumin is coagulated at about 170° Fahr.; the
higher temperature, which it is found necessary to employ, overcooks
the meat and renders it less digestible (see also p. 40).