hen
treated with disinfectants,--experiments which were supposed at that
time to be the foundation of the bacterial theory of casein
digestion--are now explicable on an entirely different basis. In these
cases the casein was not peptonized, because these strong disinfectants
destroyed the activity of the enzyms as well as the bacteria.

Another important factor in the breaking down of the casein is the
_pepsin_ in the rennet extract. The digestive influence of this agent
was first demonstrated for cheddar cheese by Babcock, Russell and
Vivian,[206] and simultaneously, although independently, by Jensen[207]
in Emmenthaler cheese. In this digestive action, only albumoses and
higher peptones are produced. The activity of pepsin does not become
manifest until there is about 0.3 per cent. acid which is approximately
the amount developed in the cheddar process. These two factors
undoubtedly account for by far the larger proportion of the changes in
the casein; and yet, the formation of ammonia in well ripened cheese is
not accounted for by these factors. This by-product is the main end
product of proteid digestion by the liquefying bacteria but their
apparent infrequency in cheese makes it difficult to understand how they
can function prominently in the change, unless the small quantity of
digestive enzyms excreted by them in their growth in milk is capable of
continuing its action until a cumulative effect is obtained. Although
much light has been thrown on this question by the researches of the
last few years, the matter is far from being satisfactorily settled at
the present time and the subject needs much more critical work. If
liquefying bacteria abound in the milk, doubtless they exert some
action, but the role of bacteria is doubtless much greater in the
production of flavor than in the decomposition of the curd.

~Conditions determining quality.~ In determining the quality of cheese,
several factors are to be taken into consideration. First and foremost
is the flavor, which determines more than anything else the value of the
product. This should be mild and pleasant, although with age the
intensity of the same generally increases but at no time should it have
any bitter, sour, or otherwise undesirable taste or aroma. Texture
registers more accurately the physical nature of the ripening. The
cheese should not be curdy and harsh, but should yield quite readily to
pressure under the thumb, becoming on manipulation waxy