Butter--32 to 34F (0 to 1C).
Leafy vegetables--35F (2C).
Root vegetables--50F (10C).
b. Relative Humidity. This is the amount of moisture in the air in relation to the
total amount of water vapor that the air can hold at a given temperature. It is expressed
in percent. Relative humidity that is higher than optimum humidity results in molding
and rotting, which lower than optimum humidity results in wilting and dehydration.
Humidity requirements for various items of subsistence are:
Eggs--88 to 90 percent.
Leafy vegetables--95 percent.
Root vegetables--85 percent.
Fruits--85 to 90 percent.
c. Air Movement. Air movement is especially necessary over fresh fruit and
fresh vegetables to dissipate the heat of respiration and the pungent odors. Air
movement affects humidity, so it must be controlled. Doubling the velocity of air moving
across a product will increase the loss of moisture in the food by one-third.
3-19. PRESERVATION BY FREEZING
Freezer storage of meats is practiced largely to equalize the supply of meat
available at all seasons of the year. Freezing preserves meat by lowering its
temperature below the growth range of most microorganisms, and freezing at 15F
(-9.4C) or lower will deny moisture so that no microorganisms can grow. Bacterial
growth will not normally occur below 23F (-5C). Virtually all-microbial growth (some
spores excepted) ceases at 0F (-18C). Mold growth will not occur below 15F
(-9.4C), because below 15F the moisture content is lowered to 6 percent and molds
will not grow in 6 percent moisture. See figure 3-1. The figure demonstrates
temperature, moisture, and ice relationship. Generally speaking, freezing has no
immediate effect on the bacterial count, but there will be a gradual reduction with the
passage of time. Lean beef will contain about 70 percent moisture. As the temperature
of meat is lowered below its freezing point (beef 29.5F (-1.4C)), moisture is
transformed into ice. A point will be reached at which no microorganisms will grow
because there will be an insufficient quantity of free or available moisture. There are
two methods of commercial freezing: sharp freezing and quick air freezing. Products to
be frozen should be wrapped to prevent dehydration.