inging about
physical and chemical changes incident to cooking.[13]

29. Bacteriological Changes.--The bacterial organisms of foods are
destroyed in the cooking, provided a temperature of 150 deg. F. is reached
and maintained for several minutes. The interior of foods rarely reaches
a temperature above 200 deg. F., because of the water they contain which is
not completely removed below 212 deg. One of the chief objects in cooking
food is to render it sterile. Not only do bacteria become innocuous
through cooking, but various parasites, as trichina and tapeworm, are
destroyed, although some organisms can live at a comparatively high
temperature. Cooked foods are easily re-inoculated, in some cases more
readily than fresh foods, because they are in a more disintegrated
condition.

In many instances bacteria are of material assistance in the preparation
of foods, as in bread making, butter making, curing of cheese, and
ripening of meat. All the chemical compounds of which foods are
composed are subject to fermentation, each compound being acted upon by
its special ferment body. Those which convert the proteids into soluble
form, as the peptonizing ferments, have no action upon the
carbohydrates. A cycle of bacteriological changes often takes place in a
food material, one class of ferments working until their products
accumulate to such an extent as to prevent their further activity, and
then the process is taken up by others, as they find the conditions
favorable for development. This change of bacterial flora in food
materials is akin to the changes in the vegetation occupying soils. In
each case, there is a constant struggle for possession. Bacteria take a
much more important part in the preparation of foods than is generally
considered. As a result of their workings, various chemical products, as
organic acids and aromatic compounds, are produced. The organic acids
chemically unite with the nutrients of foods, changing their composition
and physical properties. Man is, to a great extent, dependent upon
bacterial action. Plant life also is dependent upon the bacterial
changes which take place in the soil and in the plant tissues. The
stirring of seeds into activity is apparently due to enzymes or soluble
ferments which are inherent in the seed. A study of the bacteriological
changes which foods undergo in their preparation and digestion more
properly belongs to the subject of bacteriology, and in this work only
brief m