CHEESE

Cheese consists essentially of the caseine and albumen of milk,
together with water, fat, lactic acid, and mineral salts. It is
prepared by the coagulation of milk by means of rennet, and is usually
obtained from cow’s milk (either fresh, skimmed, or sour), although
the milk of the goat, ewe, and other animals is occasionally used.
Its colour is very often due to the addition of annato. The following
table exhibits the composition of the best-known varieties of cheese,
according to the analysis of various chemists:–

—————-+———-+———-+———–+———+———
| | | Caseine | |
| | | or | | Free
Variety. | Water. | Fat. |Nitrogenous| Milk | Acid, as
| | | Matter. | Sugar. | Lactic.
—————-+———-+———-+———–+———+———
|per cent. |per cent. | per cent. |per cent.|per cent.
American (pale) | 31·55 | 35·93 | 28·83 | .. | 0·27
American (red) | 28·63 | 38·24 | 29·64 | .. | ..
Cheddar | 35·60 | 31·57 | 28·16 | .. | 0·45
Stilton | 23·57 | 39·13 | 32·55 | .. | 1·24
Gloucester | 35·75 | 28·35 | 31·10 | .. | 0·31
Dutch | 41·30 | 22·78 | 28·25 | .. | 0·57
Roquefort | 32·26 | 34·38 | 27·16 | .. | 1·32
Brie | 51·87 | 24·83 | 19·00 | .. | ..
Cheshire | 37·11 | 30·68 | 26·93 | .. | 0·86
Gruyère | 33·66 | 30·69 | 30·67 | .. | 0·27
Gorgonzola | 31·85 | 34·34 | 27·88 | .. | 1·35
Neufchatel | 37·87 | 41·30 | 17·43 | |
| | | | \ /
Camembert | 51·30 | .. | 19·00 | 3·50
| | | | / \
Parmesan | 27·56 | 15·95 | 44·08 | 6·69
—————-+———-+———-+———–+——————-

—————-+———+———————
| | Composition of Fat.
| +———-+———-
Variety. | Ash. | Soluble | Insoluble
| | Acids. | Acids.
—————-+———+———-+———-
|per cent.|per cent. | per cent.
American (pale) | 3·42 | 4·81 | 88·49
American (red) | 3·49 | 4·26 | 89·06
Cheddar | 4·22 | 4·55 | 88·75
Stilton | 3·51 | 4·42 | 88·76
Gloucester | 4·49 | 6·68 | 86·89
Dutch | 7·10 | 5·84 | 87·58
Roquefort | 4·88 | 4·91 | 88·70
Roquefort | 5·00 | .. | ..
Brie | 4·42 | 5·55 | 87·76
Cheshire | 4·71 | 4·41 | 88·97
Gruyère | 4·58 | 4·40 | 89·18
Gorgonzola | 3·40 | .. | ..
Neufchatel | | |
Camembert | 4·70 | .. | ..
| | |
Parmesan | 5·72 | .. | ..
—————-+———+———-+———-

Dr. Muter has published the following analyses of cheese:–[47]

—————–+—————————————————-
|Insoluble Acids.
| +———————————————-
| |Soluble Acids.
| | +—————————————–
| | |Milligrammes K(OH) to saponify 1 gr.
| | | +———————————–
| | | |Water.
| | | | +—————————–
| | | | |Fat.
| | | | | +———————–
Variety. | | | | | |Lactic Acid.
| | | | | | +—————–
| | | | | | |Insoluble Ash.
| | | | | | | +———–
| | | | | | | |Soluble
| | | | | | | | Ash.+—–
| | | | | | | | |Salt.
—————–+—–+—-+—–+—–+—–+—–+—–+—–+—–
Double Gloucester|87·00|6·28|229·3|37·20|22·80|1·80 |2·56 |2·00 |1·64
Stilton |86·20|7·02|231·7|28·60|30·70|1·08 |1·80 |2·22 |0·75
English cream |90·01|3·26|220·0|63·64|15·14|0·90 |0·72 |0·20 |0·12
Dutch |87·20|6·09|228·7|42·72|16·30|1·35 |2·26 |9·10 |4·02
Gruyère |87·32|5·98|228·0|33·20|27·26|1·35 |3·12 |1·58 |1·05
Rochefort |87·00|6·27|229·3|21·56|35·96|0·72 |1·70 |8·54 |3·42
Camembert |87·15|6·09|229·0|48·78|21·35|0·36 |0·16 |8·64 |3·46
Bondon |7·834|5·95|228·0|55·20|20·80|0·90 |0·52 |6·46 |3·16
American Cheddar |89·08|3·30|220·2|29·70|30·70|0·90 |2·16 |1·54 |1·20
Cheddar |87·66|5·00|227·5|33·40|26·60|1·53 |2·30 |2·00 |1·52
—————–+—–+—-+—–+—–+—–+—–+—–+—–+—–

According to this chemist, one gramme of genuine cheese should require
not less than 220 milligrammes K(OH) for saponification, as executed in
Koettstorfer’s process (see p. 71).

The following results were obtained by Griffiths[48] from the analysis
of American cheese, and by Gerber[49] from the analysis of artificial
American cheese:–

————–+———+————+————–
| American|Lard Cheese.|Oleomargarine
| Cheese.| | Cheese.
————–+———+————+————–
|per cent.| per cent. | per cent.
| | |
Water | 26·55 | 38·26 | 37·99
Fat | 35·58 | 21·07 | 23·70
Caseine, etc. | 33·85 | 35·55 | 34·65
Ash | 3·90 | 5·12 | 3·66
————–+———+————+————–

The constituents of cheese are very similar to those of milk; the
relations between the soluble and insoluble fatty acids is much the
same as in butter. In cheese, however, the milk-sugar is largely
decomposed into lactic acid, alcohol, and carbonic acid, during the
process of ripening or curing employed in its manufacture.

Another essential change effected by the curing of cheese is the
partial decomposition of the caseine into ammonia, which combines
with the unaltered caseine, forming soluble ammonium caseates. Other
products of the ripening process, also due to the decomposition of the
caseine, are tyrosine and leucine (C_{6}H_{13}NO_{2}). The butter-fats
are likewise transformed into the corresponding fatty acids, which give
rise to the formation of either the ammonia salts, acid albuminates, or
amines, such as butylamine or amylamine.

The characteristic odour of many varieties of cheese is chiefly owing
to the genesis of these latter compounds.

As with butter, the most important adulteration of cheese consists
in the addition of foreign fats. Doubtless, the most frequent
sophistication is the admixture of lard. Lard cheese (which is usually
sold as “Neufchatel”) is made by first preparing an emulsion of lard
and skimmed milk (in the proportion of one part of the former to two
parts of the latter). This is subsequently incorporated with skimmed
milk and butter-milk, the coagulation of the fat being then effected
in the usual manner. In regard to the production of this species of
cheese, it is stated that in the 23 factories in the State of New
York, the product of six months’ working (ending November, 1881), was
about 800,000 pounds, of which the greater proportion was exported.
The recent (1885) adoption of a New York State brand for “pure cream
cheese” has had a very good effect, and accomplished much in the
restriction of the manufacture and sale of the spurious article.
Another variety of imitation cheese, know as “anti-huff cheese,”
is prepared from skimmed milk without the addition of foreign fat,
but with the aid of various chemical preparations, such as caustic
or carbonated soda, saltpetre, and borax. The rind of cheese is
occasionally contaminated with poisonous metallic salts, including
those of lead, mercury, antimony, arsenic, copper and zinc, which are
added either for colouring purposes or to prevent the attacks of flies
and other insects. This form of adulteration is doubtless of rare
occurrence. The methods used in cheese analysis are much the same as
those employed in the examination of butter. The fat is determined
by exhaustion with ether (or preferably, petroleum naphtha), and
evaporation, the remaining solids not fat being likewise dried and
weighed. The difference between the combined weight of the fat and the
solids not fat, and the amount of the sample taken, represents the
proportion of water present. Lactic acid, while insoluble in petroleum
naphtha, is also dissolved by ether, and can be estimated by digesting
another portion of the sample with water, and titrating the filtered
liquid with decinormal soda solution. Its weight is then to be deducted
from the amount of fat previously obtained, in case ether was employed
in this determination. The relative proportions of the soluble and
insoluble fatty acids contained in cheese possess the same significance
in indicating the presence of oleomargarine and other foreign fats as
with butter; and they are determined by the same methods.

The examination of the colouring matter of cheese can be made by first
neutralising the free lactic acid, separating the fat by agitation
with water, filtering and drying; the fat is then tested with carbon
disulphide and potassium hydroxide (see p. 77).

FOOTNOTES:

[47] ‘Analyst,’ Jan. 1885, p. 3.

[48] Chem. News, pp. 47, 85.

[49] Dingl., vol. i. pp. 247, 474.

FLOUR AND BREAD.

Wheat (_Triticum vulgare_) forms the principal bread-stuff of civilized
nations, and is by far the most important of all cereal grasses. It
has one or more slender, erect and smooth stalks, which, owing to the
large proportion of siliceous matter present, possesses the strength
necessary for the support of the ears. The grain is imbricated in four
rows. The following are the averages of the results obtained by the
analyses of 260 samples of American wheat, made by the United States
Department of Agriculture, in 1883:–

Per cent.
Water 10·27
Ash 1·84
Oil 2·16
Carbohydrates 71·98
Fibrin 1·80
Albuminoids 11·95
Nitrogen 1·91

Analyses of the ash of wheat by the same Department, furnished the
following results:–

—————-+———+——————-
| | Foreign.
| Dakota. +———+———
| | Winter. | Spring.
—————-+———+———+———
|Per cent.|Per cent.|Per cent.
Insoluble | 1·44 | 2·11 | 1·64
Phosphoric acid | 47·31 | 46·98 | 48·63
Potassa | 30·63 | 31·16 | 29·99
Magnesia | 16·09 | 11·97 | 12·09
Lime | 3·36 | 3·34 | 2·93
Soda | 1·17 | 2·25 | 1·93
Sulphuric acid | trace | 0·37 | 0·48
Chlorine | „ | 0·22 | 0·51
Ferric oxide | „ | 1·31 | 0·28
Undetermined | .. | 0·29 | 1·52
| —— | —— | ——
| 100·00 | 100·00 | 100·00
| | |
Total ash | 1·88 | 1·97 | 2·14
—————-+———+———+———

FLOUR.

The name flour is usually given to the product obtained by grinding
wheat and removing the bran, or woody portion of the grain, by sifting
or bolting. Its constituents are starch, dextrine, cellulose, and sugar
(carbohydrates), the nitrogenous compounds albumen, gliadin, mucin,
fibrin, and cerealin, and fat, mineral substances and water. Upon
kneading flour with water, and removing the starch and soluble matters
by repeated washing, an adhesive body termed _gluten_ remains behind.
This is chiefly composed of gliadin, mucin, and fibrin.

According to Wanklyn,[50] the general composition of flour is:–

Per cent.
Water 16·5
Fat 1·5
Gluten 12·0
Modified starch 3·5
Vegetable albumen 1·0
Starch granules 64·8
Ash 0·7

The average of numerous analyses of American flour examined by the
Department of Agriculture gave:–

Per cent.
Water 11·67
Fat 1·25
Sugar 1·91
Dextrine 1·79
Starch 71·72
Soluble albuminoids 2·80
Insoluble „ 7·90
Total „ 10·70
Ash 0·54

The composition of the ash of flour from Minnesota wheat (1883), is as
follows:–

Per cent.
Insoluble 0·98
Phosphoric acid 49·63
Potassa 31·54
Magnesia 9·05
Lime 5·87
Soda 2·93

ANALYSIS OF FLOUR.

The following are the determinations generally required in the
proximate analysis of flour:–

_Water._–Two or three grammes of the sample are weighed in a tared
platinum dish, and heated in an air bath, until constant weight is
obtained. The proportion of water should not exceed 17 per cent.

_Starch._–A small amount of the flour is placed in a flask, connected
with an ascending Liebig’s condenser, and boiled for several hours with
water slightly acidulated with sulphuric acid. Any remaining excess
of acid is then neutralised with sodium hydroxide; the solution is
considerably diluted, and the glucose formed, estimated by means of
Fehling’s solution (see p. 111). 100 parts of glucose represent 90
parts of starch.

_Fat._–The inconsiderable proportion of fat in flour is best
determined by exhausting the dried sample with ether and evaporating
the solution.

_Gluten_ (albuminoids).–As previously stated, gluten is separated by
kneading the flour and repeated washing with water. After the removal
of the amylaceous and soluble ingredients, the residue is carefully
dried and weighed. A far more accurate method is to make a combustion
of a small portion of the flour with cupric oxide, and determine the
quantity of nitrogen obtained, the percentage of which, multiplied by
6·33, gives the percentage of gluten.[51] The proportion of gluten in
flour ranges from about 8 to 18 per cent. From 10 to 12 per cent, is
deemed necessary in order to make good bread, and, in England, any
deficiency in this constituent is remedied by the addition of bean or
other flour, but in the United States this practice is seldom required.

_Substances soluble in cold water._–About five grammes of the flour
are digested with 250 c.c. of cold water, and the solution filtered,
and evaporated to dryness. Good flour is stated to yield 4·7 per cent.
of extract when treated in this manner, the soluble matters consisting
of sugar, gum, dextrine, vegetable albumen, and potassium phosphate.
The latter salt, which constitutes about 0·4 per cent. of the extract,
should form the only mineral matter present.

_The Ash._–The ash of flour is determined in the usual manner, by
ignition in a platinum dish. It varies in amount from 0·3 to 0·8 per
cent., and should never exceed a proportion of 1·5 per cent.

When of good quality, wheaten flour is perfectly white, or has only a
faint tinge of yellow. It should be free from bran, and must not show
red, grey, or black specks, nor possess a disagreeable odour. It should
also exhibit a neutral reaction and a decided cohesiveness, acquiring
a peculiar soft and cushion-like condition when slightly compressed.
Formerly, wheaten flour was mixed with various foreign meals, such as
rye, corn, barley, peas, beans, rice, linseed, buckwheat, and potato
starch; but at present this form of adulteration is probably but
rarely resorted to, at least in the United States. The presence of
mildew, darnel, ergot, and other parasites of the grain, constitutes
an occasional contamination of flour. The most frequent admixture
consists, however, in the addition of alum, which, although more
extensively used in bread, is also employed in order to disguise the
presence of damaged flour in mixtures, or to improve the appearance of
an inferior grade; its addition to a damaged article serves to arrest
the decomposition of the gluten, thereby preventing the flour from
acquiring a dark colour, and disagreeable taste and odour.

It has recently been stated that in flour which has been kept for a
long time in sacks, a transformation of the gluten sometimes occurs,
resulting in the production of a poisonous alkaloid. This body may be
separated by evaporating the ethereal extract of the flour to dryness,
and treating the residue with water. The presence of the alkaloid in
the filtered aqueous solution is recognised by means of potassium
ferrocyanide. The presence of an excessive proportion of moisture is
doubtless instrumental in the formation of toxic alkaloids or fungi in
old flour and bread.

Pure wheaten flour is coloured yellow when treated with ammonium
hydroxide, whereas corn meal assumes a pale brown colour, and the meals
prepared from peas, beans, etc., become dark brown in colour when
tested in this way. Nitric acid imparts an orange-yellow colour to
wheaten flour, but fails to change the colour of potato-starch, with
which it forms a stiff and tenacious paste.

Potato-starch is readily detected by examining a thin layer of the
sample on a slide under the microscope, and adding a dilute solution
of potassium hydroxide, which, while not affecting the wheaten starch,
causes the potato-starch granules to swell up very considerably.
Leguminous starches, such as peas, etc., contain approximately 2·5 per
cent. of mineral matter; in pure flour, the average proportion of ash
is only about 0·7 per cent., and this difference is sometimes useful in
the detection of an admixture of the former.

The external envelope of the granules of potato-starch offers far less
resistance when triturated in a mortar than that of wheat, and upon
this fact a simple test for their detection is founded. It is executed
by rubbing up a mixture consisting of equal parts of the sample and
sand with water, diluting and filtering the paste formed, and then
adding to it a solution of 1 part of iodine in 20 parts of water. In
the absence of potato-starch, an evanescent pink colour is produced;
in case it is present, the colour obtained is dark purple, which in
time also disappears.

Among the methods which have been suggested for the detection of
such accidental impurities as darnel, ergot, and mildew, are the
following:–If pure flour is digested for some time with dilute
alcohol, the latter either remains quite clear or it acquires a very
light straw-colour; with flour contaminated with darnel, the alcohol
shows a decided greenish tint, and possesses an acrid and disagreeable
taste. In case the alcohol used is acidulated with about 5 per cent.
of hydrochloric acid, the extract obtained exhibits a purple-red
colour with flour containing mildew, and a blood-red colour with flour
containing ergot. When flour contaminated with ergot or other moulds,
is treated with a dilute solution of aniline violet, the dye is almost
wholly absorbed by the damaged granules, which are thus rendered more
noticeable in the microscopic examination.

The following test is often used for the detection of alum in flour:–A
small quantity of the suspected sample is made into a paste with a
little water and mixed with a few drops of an alcoholic tincture of
logwood; a little ammonium carbonate solution is then added. In the
presence of alum, a lavender-blue coloured lake is formed, which
often becomes more apparent upon allowing the mixture to remain at
rest for a few hours. The production of a brown or pink coloration is
an indication of the absence of alum. A modification of this test,
proposed by Blyth, consists in immersing for several hours in the cold
aqueous extract of the flour a strip of gelatine, with which the alum
combines; the gelatine is subsequently submitted to the action of the
logwood tincture and ammonium carbonate as above.

For the quantitative estimation of alum in flour, the following
processes are usually employed:–A considerable quantity of the sample
is incinerated in a platinum dish, the ash is boiled with dilute
hydrochloric acid and the solution filtered. The filtrate is next
boiled and added to a concentrated solution of pure sodium hydroxide,
the mixture being again boiled and afterwards filtered hot. A little
sodium diphosphate is now added to the filtrate which is then slightly
acidulated with hydrochloric acid, and finally made barely alkaline by
addition of ammonium hydroxide. The resulting precipitate, which, in
the presence of alum, consists of aluminium phosphate, is brought upon
a filter, well washed, and then weighed.

Another method, which is a modification of that of Dupré, is as
follows:–The ash obtained by the calcination of the flour (or bread),
is fused, together with four times its weight of pure mixed sodium and
potassium carbonates, the fused mass treated with hydrochloric acid,
the solution evaporated to dryness and the separated silica collected
and weighed. A few drops of sodium phosphate solution are added to
the filtrate from the silica, then ammonium hydroxide in excess, by
which the calcium, magnesium, ferric and aluminium phosphates are
precipitated. The two latter are next separated by boiling the liquid
with an excess of acetic acid (in which they are insoluble), and
brought upon a filter, washed, dried, and weighed. The iron sometimes
accompanying the precipitate of aluminium phosphate, can be determined
by reduction with zinc and titration with potassium permanganate.
If the presence of alum is indicated by the logwood test, and it is
quantitatively determined by either of the preceding methods, it has
been suggested that an allowance be made for the small proportion of
aluminium silicate occasionally found in unadulterated flour or bread,
and a deduction from the total alum present of one part of alum for
every part of silica obtained is considered proper. The weight of
aluminium phosphate found, multiplied by 3·873, or by 3·702, gives
respectively the corresponding amounts of potash-alum or ammonia-alum
contained in the sample examined.

BREAD.

Bread is usually prepared by mixing flour with water, kneading it into
a uniform dough, submitting it to a process of “raising,” either by
means of a ferment or by the direct incorporation of carbonic acid gas,
and finally baking the resulting mass.

Unleavened bread, however, is made by simply kneading flour with water,
with the addition of a little salt, and baking. The oatcake of the
Scotch, the passover bread of the Israelites, and the corncakes of the
Southern States are the best known varieties of unleavened bread.

The porosity peculiar to raised bread is caused by the generation of
a gas, either previous to, or during the process of baking. In former
times (and to some extent at present, notably in Paris), fermented
bread was made by the use of _leaven_, which is dough in a state of
incipient decomposition; but in this country, the common agent employed
in raising bread is yeast, which consists of minute vegetable cells
(_Torula cerevisiæ_) forming either the froth or deposit of fermenting
worts.

By the action of these ferments, the gluten of the flour first
undergoes a modification and enters into a peculiar combination with
the starch-granules, which become more or less ruptured; the soluble
albumen is rendered insoluble, and the starch is transformed, first
into sugar, then into carbonic acid and alcohol. These changes are
perfectly analogous to those which occur in the fermentation of the
wort in the preparation of fermented liquors.

Other and minor decompositions likewise occur, such as the partial
conversion of the starch into dextrine, the sugar into lactic acid,
and the alcohol into acetic acid, but the most essential change is the
production of alcohol and carbonic acid. The alcohol formed is mainly
volatilised, although an average proportion of 0·3 per cent. of this
compound has been found in samples of fresh bread. The escape of the
carbonic acid is retarded by the gluten, and to its expansion is due
the porous or spongy appearance of well-made bread.

Of late years, artificial substitutes for the fermentation process in
the production of porous bread have been extensively employed. By the
use of these agents, the liberation of carbonic acid in the dough is
accomplished and a slight gain of weight is effected, as none of the
original ingredients of the flour are lost by fermentation.

“Aërated bread” is made by kneading the flour under pressure with water
highly charged with carbonic acid gas, which, upon the removal of the
pressure, expands, and gives porosity to the bread. The use of “baking
powders” effects the same result in a more convenient manner, and is
largely practised in families. These compounds generally consist of
sodium bicarbonate (sometimes partially replaced by the corresponding
ammonia salt), and tartaric acid, or potassium bitartrate, together
with rice or other flour. A more commendable preparation is a mixture
of sodium bicarbonate with potassium or calcium acid phosphates, the
use of which is claimed to restore to the bread the phosphates lost by
the removal of the bran from the flour. Baking powders are often mixed
in the dry state with flour, and the produce, which is known under the
name of “self-raising flour,” only requires to be kneaded with water
and baked to form porous bread. However great the convenience attending
the use of these compounds, they are often open to the objection that
their decomposition gives rise to the formation of aperient salts,
_e.g._ sodium tartrate, and that they are very frequently contaminated
with alum.

As a result of the chemical changes which take place in the
fermentation of the flour and the subsequent application of heat, the
composition of bread differs materially from that of the grain from
which it is prepared. As already mentioned, the soluble albuminoids
are rendered insoluble, and the starch is partially transformed into
sugar (maltose). The unconverted starch is modified in its physical
condition, the ruptured granules being far more readily acted upon
by the digestive fluids than before. The proportion of soluble
carbohydrates is naturally augmented in bread. The amount of ash is
also somewhat increased, chiefly owing to the addition of salt, but
it should not exceed a proportion of 2 per cent. The quantity of
water in bread varies considerably. Wanklyn fixes 34 per cent. as the
standard; greater proportions have, however, been frequently found.
In ten samples of apparently normal bread, examined by E. S. Wood,
Analyst to the Massachusetts State Board of Health, the amounts of
moisture contained varied from 34 to 44 per cent. The quantity of
water decreases very rapidly upon exposure to the air. Thus, Clifford
Richardson[52] found that bread which showed 36 per cent. of moisture
when freshly baked, contained but 5·86 per cent. after drying for two
weeks. Stale bread would seem to contain water in a peculiar molecular
condition, and, as is well known, upon heating (“toasting”), it
reassumes the porous state.

According to analyses collected by König,[53] the mean composition of
bread is as follows:–

————-+——————————————————–
|Water.
| +————————————————–
| |Nitrogenous substances.
| | +—–+——+——————————-
| | |Fat. |Sugar.| Extractive free from Nitrogen.
| | | | ++ +———–+————–
| | | | | |Cellulose. | Dry
| | | | | | +—–| Substances.
| | | | | | |Ash. |————–
| | | | | | | |Carbohydrates.
| | | | | | | |—–+
| | | | | | | | N. |
————-+—–+—–+—–+—–+—–+—–+—–+—–+——–
| per | per | per | per | per | per | per | per | per
|cent.|cent.|cent.|cent.|cent.|cent.|cent.|cent.| cent.
Fine wheat | | | | | | | | |
bread |31·51| 7·06| 0·46| 4·02|52·56|0·32 | 1·09| 1·75| 87·79
Coarse | | | | | | | | |
wheat bread|40·45| 6·15| 0·44| 2·08|49·04|0·62 | 1·22| 1·65| 85·84
Rye bread |42·27| 6·11| 0·43| 2·31|46·94|0·49 | 1·46| 1·69| 85·31
Pumpernickel |43·42| 7·59| 1·51| 3·25|41·87|0·94 | 1·42| 2·15| 79·74
————-+—–+—–+—–+—–+—–+—–+—–+—–+——–

Clifford Richardson gives the following results of the analysis of
ordinary family loaf-bread:–

Per cent.
Water 37·30
Soluble albuminoids 1·19
Insoluble „ 6·85
Fat 0·60
Sugar 2·16
Dextrine 2·85
Starch 47·03
Fibre 0·85
Ash 1·17
——
100·00

Nitrogen 1·29
Total albuminoids 8·04

The analysis of bread is conducted essentially in the same manner
as that of flour. Under ordinary circumstances, the determinations
required are limited to an estimation of the moisture contained in
the crumb, the amount of the ash, and special tests for the presence
of alum and copper salts. Owing to the broken condition of the starch
granules in bread, their identification by the microscope is usually
rendered exceedingly difficult. The logwood test for alum in bread
is applied by Bell as follows:–About 10 grammes of the crumb are
immersed in a little water containing 5 c.c. each of the freshly
prepared logwood tincture and solution of ammonium carbonate for about
five minutes, after which the liquid is decanted, and the bread dried
at a gentle heat. In the presence of alum the bread will acquire
the characteristic lavender tint mentioned under Flour. It should
be added, that salts of magnesia also produce a lavender lake with
alum; but this fact does not affect the usefulness of the process as
a preliminary test to the quantitative determination of the mineral
impurities present in the sample under examination. The quantitative
examination of alum in bread is made by one of the methods described on
p. 93. Bread, free from alum, will sometimes yield 0·013 per cent. of
aluminium phosphate, and this amount should therefore be deducted from
the weight of the precipitate obtained.

The average of the results obtained by Dr. Edward G. Love, New York
State Board of Health, from the examination of the crumb of ten samples
of the cheaper varieties of wheaten bread were as follows:–

Per cent.
Water 42·80
Total ash 1·0066
Silica and sand 0·0056
Aluminium (and ferric) phosphates 0·0053

That the addition of alum to bread is prevalent seems to admit of
little doubt. The British Public Analysts, in 1879, tested 1287 samples
of bread, of which 95 (or 7·3 per cent.) contained alum. Of 18 samples
examined, in 1880, in the city of Washington, 8 were adulterated with
the salt. The question of the sanitary effects produced by the use of
alumed bread is one which has given rise to very extended discussion.
According to some authorities, the conversion of alum into an insoluble
salt by the fermentation process, which takes place in bread-making,
is regarded as a proof that it remains inert, and is consequently
harmless in its effects. Others contend that its action as a preventive
of excessive fermentation is at the expense of valuable nutritious
constituents of the flour, and that its combination with the phosphates
present in the grain results in the formation of an insoluble salt
which tends to retard digestion. Experiments have been made by J. West
Knights, on the comparative action of artificial gastric juice upon
pure and alumed bread, which apparently support this latter view.

Another objection to the use of alum is that it is frequently employed
for the purpose of disguising the bad quality of damaged and inferior
grades of flour. The presence of copper salts in bread is of rare
occurrence. Their detection is accomplished by treating a portion
of the crumb with a dilute solution of potassium ferrocyanide
acidulated with acetic acid, which, in presence of copper, will impart
a reddish-brown colour to the bread. If contained in any appreciable
proportion, it can be extracted from the ash obtained by the
incineration of the bread, and deposited upon the interior of a weighed
platinum capsule by the electrolytic method.

_Starch_ (C_{6}H_{10}O_{5}).–Starch, which enters so largely into the
composition of cereals, is a carbo-hydrate, _i. e._ hydrogen and oxygen
are contained in the proportions necessary to form water. In this
respect, it is identical with woody fibre, cellulose, and dextrine.

The well-known dark-blue colour produced upon the addition of a
solution of iodine to starch-paste forms the usual qualitative test
for its presence. This coloration is discharged by alkalies and by a
solution of sulphurous acid. The quantitative estimation of starch in
mixtures is best effected by heating the dry substance in a closed
tube for 24 hours, together with a dilute hot alcoholic solution of
potassium hydroxide. The hot liquid is next filtered, the residue
washed with alcohol, and the filtrate heated with 2 per cent. solution
of hydrochloric acid until it ceases to show the blue coloration when
tested with iodine. It is then rendered alkaline, and the proportion of
starch originally present, calculated from the amount of sugar formed,
as determined by Fehling’s solution. Although identical in chemical
composition, the various forms of starch met with in the vegetable
kingdom vary in size and exhibit characteristic differences in the
appearance of the granules. The following are measurements of several
varieties of starch granules:–

Millimetre.
Wheat ·0500
Rye ·0310
Rice ·0220
Corn ·0300
Bean ·0631
Potato ·1850

The larger granules of potato starch, when suspended in water, subside
more rapidly than those of wheat starch; they are also far more readily
ruptured.

The identification of the various starches is accomplished by means
of the microscope. Starch possesses an organised structure which,
fortunately, differs in different plants. Besides varying in size,
the granules develope in a different manner and form from centres of
growth, and therefore exhibit characteristic conditions and positions.
These distinctions, together with their effect upon polarised light,
are of great utility in the determination of the source of any
particular starch. For this purpose, it is necessary to become familiar
with the distinctive microscopical appearance of each individual
starch. A collection of those most usually met with should be made,
and, after careful study, preserved in a dried state for comparative
purposes. Polarised light is a very useful adjunct in the examination
of starch granules. In the microscopical investigation, a minute
portion of the sample is placed upon the glass slide and well moistened
with a solution of 1 part glycerine in 2 parts of water; it is then
protected by a thin glass cover, which is put on with gentle pressure.
The appearance of various starches, under polarised light, is seen in
Plate IX., where the cross lies at the hilum or nucleus of the granule
and the form and relative size is visible in outline. This plate, and
Plates VII. and XII. are copied, with permission, from Bulletin No. 11
of the Chemical Division of the U.S. Department of Agriculture. The
original negatives (made by Clifford Richardson) were used, but the
auto-types are presented in a somewhat modified form.