m from
coming in contact with iron or copper.

[Illustration: Fig. 33.--Moldy Butter.

The mold grows on the paper in which the butter is wrapped rather
than on the butter. The print on the left was wrapped in the same
paper as the print on the right except that the parchment cover had
been steamed for a few moments.]

=Moldy butter.= A defect that causes a great amount of loss is the
development of mold on the surface of the butter, either in tubs
or in prints. This trouble is easily prevented. Butter is not well
suited to the growth of mold, but the paper used for lining the
tubs, or wrapping the prints is an excellent medium for mold growth.
The wood of the tub also furnishes ample food for this type of life,
especially where the wood contains any sap. One other essential
condition for mold growth is a supply of oxygen. The mold spores are
widely disseminated, and are always to be found on the butter tubs
and on the paper. The number is not likely to be sufficient to cause
trouble unless the tubs and paper have been kept under such
conditions, as to allow growth to take place on them before use.
During damp, hot weather, the amount of moisture absorbed by these
materials is often sufficient to allow molds to grow on them. This
trouble can be prevented by the storage of tubs and paper in a clean
dry place, or by a disinfecting treatment which will destroy the
mold spores. The most successful method of treatment of tubs is to
apply paraffin to the inner surface, which can be easily done by the
use of some one of the various machines now on the market. The
thin layer of paraffin excludes the moisture from the wood, and also
prevents the mold from obtaining a supply of oxygen for its growth.
The tubs may be steamed, treated with hot water, or filled with a
dilute solution of formaldehyde, and allowed to stand overnight.
Soaking in brine as is usually done in the creameries is of some
effect, but will not completely kill mold spores.

[Illustration: Fig. 34.--Moldy Butter.

The butter was placed in a paraffined tub, but the paper was not
treated so as to destroy the mold spores thereon.]

Butter may mold where the tubs have been thoroughly treated, because
of the mold spores on the paper used for the lining. One of the
black molds is able to thrive on parchment paper whenever the air is
damp. In the past but little attention has been paid to the paper as
a source of trouble. It is certain that it is often at fault