adually it breaks down and becomes plastic, the elastic, tough curd
being changed into a softened mass. This change in texture of the cheese
is also accompanied by a marked change in flavor. The green cheese has
no distinctively cheese flavor, but in course of time, with the gradual
change of texture, the peculiar flavor incident to ripe cheese is
developed.

The characteristic texture and flavor are susceptible of considerable
modification that is induced not only by variation in methods of
manufacture, but by the conditions under which the cheese are cured. The
amount of moisture incorporated with the curd materially affects the
physical appearance of the cheese, and the rate of change in the same.
The ripening temperature, likewise the moisture content of the
surrounding air, also exerts a marked influence on the physical
properties of the cheese. To some extent the action of these forces is
purely physical, as in the gradual loss by drying, but in other respects
they are associated with chemical transformations.

~Chemical changes in ripening cheese.~ Coincident with the physical
breaking down of the curd comes a change in the chemical nature of the
casein. The hitherto insoluble casein is gradually transformed into
soluble nitrogenous substances (_caseone_ of Duclaux, or _caseogluten_
of Weigmann). This chemical phenomenon is a breaking-down process that
is analogous to the peptonization of proteids, although in addition to
the peptones and albumoses characteristic of peptic digestion,
amido-acids and ammonia are to be found. The quantity of these lower
products increases with the age of the cheese.

The chemical reaction of cheese is normally acid to phenolphthalein,
although there is generally no free acid, as shown by Congo red, the
lactic acid being converted into salts as fast as formed. In very old
cheese, undergoing putrefactive changes, especially on the outside, an
alkaline reaction may be present, due to the formation of free ammonia.

The changes that occur in a ripening cheese are for the most part
confined to the proteids. According to most investigators the fat
remains practically unchanged, although the researches of Weigmann and
Backe[185] show that fatty acids are formed from the fat. In the green
cheese considerable milk-sugar is present, but, as a result of the
fermentation that occurs, this is rapidly converted into acid products.

~Bacterial flora of cheese.~ It might naturally be expected