Audubon County journal. (Exira, Iowa) 1884-1993, 1898-03-03
DElRE,k|l[EEEHMEgEl'||
RIPENING CHEESE.
Changes, Chemical and Otherwise, That
Occur During the Process.

Professors S. M. Babcock and II. T..
Russell publish in Hoard Dairyman a
valuable account of their experiments
in the chemistry and biology of cheese
ripening. 1t is the most obscure of the
operations involved in the making of
dairy products, and the professors pa
per throws light on it. Following are
extracts:
Cheese is highly heterogeneous sub
stance and is therefore susceptible OF
many fermentation changes that do not
occur in butter. Butter fat'is not suited
as a food medium for bacterial growth,
but in cheeses, even those rich in fat,
bacteria multiply very rapidly and con-
tinue to do SO for long period Of time.
When the curds are put to press, they
are firm, elastic and insoluble. Screen"
cheese as an article of diet is not very
tempting, but if the same curd is al
lowed to stand under proper conditions
for considerable period Of time it loses
its original qualities and becomes soft,
friable and readily soluble. Chemically
the change which occurs is a conversion
of the insoluble casein into soluble pep
tones, and with this breaking down Of
the casein there is developed the pecul-
lar flavor that marks we'll ripened
cheese.
In our American Cheddar cheese
within few days marked develop
ment Of bacteria occurs, particularly
those forms that are able to sour milk.
This class has been supposed by Freu
denreich and Lloyd to be the cause Of
the ripening Of cheese, but when pure
cultures Of various germs Of this GLASS
are inoculated into milk sterilized by
heat no change other than the usual
souring is to be noted. This has been
the insuperable objection to the theory
that this class was the cause Of the
breaking down changes.
This summer in the course Of some
experiments with milk to which ether
had been added we noticed that the
milk curdled and underwent digestive
changes without apparently increasing
in acidity. This fact could only be ex-
planned by assuming that bacteria could
live in this etherized milk or that GER
tain ferments of an unorganized nature
were present in the milk and that the
digestion-the conversion of the casein
into soluble peptones-was due to these
agents. By further experiments we
were able to exclude bacterial action
and show that there were naturally pres
emit in milk ferments comparable to
those that are found in the alimentary
tract and that these ferments, technical
~ known as engines, were the cause of
the spontaneous digestion Of milk.
This discovery in itself was contri-
button of some importan to the science
of physiological chemistry. for no one
has previously claimed chat milk con-
tains these digesting ferments, although
similar ferments are found in the body
juices and many of its tissues.
Although Of value from the stand
point of physiological chemistry, this
discovery is invested with far greater
significance when we study the rela-
tions which it bears to the ripening
changes in cheese.
TWAS found that milk invariably un-
derwent this decomposition if the bac-
terial lamentations were held in check
by the addition of chemicals that did
not destroy the action of these morgan
lied or chemical ferments. Among the
substances used were ether, ohloroform
and benzol. Furthermore, this change
was Of progressive character. It was
also Immediately suspended if the milk
WAS boiled or treated with strong
chemical disinfectant.
A comparative study ofthe products
formed in thase milks SO treated COM
pared with those that occur in normal
cheese showed that they were strikingly
similar.
Attempts were then made to isolate
the supposed engines, and by means of
the usual physiological methods it was
possible to separate from centrifuge
Slime certain extracts that were rela-
lively pure. Slime.wa taken for the
reason that these engines are likely to
attach themselves to solid matter held
in suspension, and this being true we
expected to find that the slime thrown
out Of the milk during its separation
would be relatively richer in these sub
stances than the whole milk. A chem
ical analysis of slime and skimmilk
showed that the change was much more
rapid in the slime, thus Indicating that
larger quantities of the ferments were
present.
While every analogy showed that
these changes were identical in charac-
ter with those that occur in normal
cheese, still we did not consider our
point conclusively proved until cheese
was made from milk that had been
kept under chloroform. The same
cheese was also kept in a saturated at
mosphere of this anasthetic for long
period Of time. Under these conditions
bacterial growth. was impossible, and
yet such cheese ripened practically as
fast as a normal cheese kept under IA
vorable conditions
1t was therefore possible to break
down the casein entirely without the
aid of bacteria. Thus the proper texture
of the curds is produced not by the ac-
ton of the Tactic acid organisms or any
other known form of living germ, but
by digestion of the casein caused nv the