=528. General Analysis.=—The cereals are prepared for analysis by
grinding until the fragments pass a sieve having circular perforations
half a millimeter in diameter. The moisture, ash, ether extract,
proteids and carbohydrates are determined by some one of the
processes already described in detail. In this country the methods
of the Association of Official Agricultural Chemists are generally
followed.[535] For convenience these methods are summarized below.
_Moisture._—Dry from two to three grams of the fine-ground sample for
five hours, at the temperature of boiling water, in a current of dry
hydrogen. If the substance be held in a glass vessel, the latter should
not be in contact with the boiling water.
_Ash._—Char from two to three grams of the sample and burn to whiteness
at the lowest possible red heat. If a white ash can not be obtained in
this manner, exhaust the charred mass with water, collect the insoluble
residue on a filter, burn it, add this ash to the residue from the
evaporation of the aqueous extract and heat the whole to low redness
until the ash is white.
_Ether Extract._—Pure ether is prepared by washing the commercial
article four or five times with water to free it of the chief part
of the alcohol it contains. The residual water is mostly removed by
treating the liquid with caustic soda or potash. Any residual alcohol
or water is finally removed by the action of metallic sodium. The
ether thus prepared is stoppered, after the evolution of hydrogen has
ceased, and is kept over metallic sodium. Immediately before use it
should be distilled out of contact with moist air.
The residue from the determination of moisture, as described above, is
extracted in an appropriate apparatus (=39=) with the pure ether for
sixteen hours. The extract is dried to constant weight. The weight may
be checked by drying and weighing the extraction tube and its contents
before and after the operation.
_Crude Proteids._—Proceed as in the method of determining nitrogen in
the absence of nitrates and multiply the weight of nitrogen obtained
by 6.25. This factor is a general one, but should not be rigidly
applied. In each instance, according to the nature of the cereal, the
appropriate factor, pointed out in paragraph =407= should be used, and
the factor 6.25 be applied only in those cases where a special factor
is not given. The factors for the common cereals are wheat 5.70, rye
5.62, oats 6.06, maize 6.22, barley 5.82 and flaxseed 5.62.
For separating the proteid matters consult paragraphs =392-410=. In the
case of wheat the methods of Teller may be consulted.[536]
_Amid Nitrogen._—The albuminoid nitrogen is determined as directed in
paragraph =203= of volume II. The difference between this number and
that representing the total nitrogen gives the nitrogen as amids.
_Fiber and Carbohydrates._—The methods of analysis are described in
detail in Part Third.
=529. Bread.=—In general, the same processes are followed in bread
analysis as are used with cereals and flours. In addition to
the regular analytical processes, breads are to be examined for
adulterants, bleaching and coloring matters, and for the purpose of
determining the changes which have taken place in their nutrient
constituents in the processes of fermentation and cooking.
_Temperature of Baking._—The interior of a loaf during the process
of baking does not attain the high temperature commonly supposed.
This temperature is rarely found to be more than one degree above the
boiling point of water.[537] In biscuits and other thin cakes, which
become practically dry and which by reason of their thinness are the
more readily penetrated by heat, the temperature may go as high as 110°.
_Soluble Extract._—The quantity of matters both in flour and bread,
soluble in cold water, is determined by extraction in the usual way
and drying the extract. Soluble albuminoids, sugars and mineral salts
are extracted by this process. When possible, the operation should be
conducted both on the bread and the flour from which it is made.
_Color._—In baker’s parlance is found an apparent contradiction of
terms, since it speaks of bread with “no color” when the loaf is dark
brown, while a white loaf is said to have a high color. An ideal
color for the interior of a loaf is a light cream tint, which is
more desirable than a pure white.[538] The texture, odor and flavor of
the loaf are also to be considered, but these are properties of more
importance to the technical expert than to the analyst.
_Quantity of Water._—It is not possible to set a rule of limitation in
respect of the quantity of water a bread should hold. For full loaves,
perhaps forty per cent is not too high a maximum, while some authors
put it as low as thirty-four per cent. Some flours are capable of
holding more water than others, and the loaf should have just enough
water to impart to the slice of bread the requisite degree of softness
and the proper texture. Most breads will have a content of water
ranging from thirty to forty per cent. In biscuits and other thin cakes
the moisture is much less in quantity.
_Acidity._—The acidity of both bread and flour is determined by shaking
ten grams of the sample with 200 cubic centimeters of distilled water
for fifteen minutes, pouring the mass on a filter and titrating an
aliquot part of the filtrate with tenth-normal alkali. The acidity is
reckoned as lactic acid in the case of breads raised by fermentation.
_Nature of Nitrogenous Compounds._—The methods of investigation are
described in paragraphs =392-410=.
=530. Determination of Alum in Bread.=—The presence of alum in bread
may be detected by means of logwood. Five grams of fresh logwood chips
are digested with 100 cubic centimeters of amyl alcohol. One cubic
centimeter of this decoction and the same quantity of a saturated
solution of ammonium carbonate are mixed with ten grams of flour and
an equal quantity of water. With pure flour, a slight pink tint is
produced. In the presence of alum the color changes to a lavender or
blue, which is persistent on heating.
The test may be varied by diluting five cubic centimeters of the
reagents mentioned with ninety cubic centimeters of water and pouring
the mixture over ten grams of the crumbled bread. After standing for
five minutes, any residual liquid is poured off and the residue, washed
once with a little water, is dried in a steam bath, when the blue color
is developed if alum be present.[539]
=531. Chemical Changes Produced by Baking.=—Changes of a chemical
nature, produced in bread by baking, are found chiefly in modifications
of the starch and proteids. The starch is partly converted into dextrin
and the albumins are coagulated. The changes in digestion coefficient
are determined by the methods which follow. The fermentations which
precede the baking are due to the usual decompositions of the
carbohydrates under the influence of yeast germs.