ugh the firm cheeses
are by no means exempt from the trouble. The "Verlaufen" or "running" of
limburger cheese is a fermentation allied to this. It is where the
inside of the cheese breaks down into a soft semi-fluid mass. In severe
cases, the rind may even be ruptured, in which case the whole interior
of the cheese flows out as a thick slimy mass, having sometimes a putrid
odor. The conditions favoring this putrid decomposition are usually
associated with an excess of moisture, and an abnormally low ripening
temperature.

~Rusty spot.~ This name is applied to the development of small
yellowish-red or orange spots that are formed sometimes throughout the
whole mass of cheddar cheese. A close inspection shows the colored
points to be located along the edges of the curd particles. According to
Harding,[216] this trouble is most common in spring and fall. The cause
of the difficulty has been traced by Connell[217] to the development of
a chromogenic bacterium, _Bacillus rudensis_. The organism can be most
readily isolated on a potato surface rather than with the usual
isolating media, agar or gelatin.

~Other pigment changes.~ Occasionally, with the hard type of cheese, but
more frequently with the softer foreign varieties, various abnormal
conditions arise that are marked by the production of different pigments
in or on the cheese. More frequently these are merely superficial and
affect only the outer layers of the cheese. Generally they are
attributable to the development of certain chromogenic organisms
(bacteria, molds and yeasts), although occasionally due to other causes,
as in the case of a blue discoloration sometimes noted in foreign cheese
made in copper kettles.[218]

De Vries[219] has described a blue condition that is found in Edam
cheese. It appears first as a small blue spot on the inside, increasing
rapidly in size until the whole mass is affected. This defect he was
able to show was produced by a pigment-forming organism, _B.
cyaneo-fuscus_. By the use of slimy whey (lange wei) this abnormal
change was controlled.

~Moldy cheese.~ With many varieties of cheese, especially some of the
foreign types, the presence of mold on the exterior is not regarded as
detrimental; in fact a limited development is much desired. In hard
rennet cheese as cheddar or Swiss, the market demands a product free
from mold, although it should be said that this condition is imposed by
the desire to secure a good-looking cheese