b. Mix Preparation. Ingredients are assembled and mixed in a vat. A vat
pasteurizer is often used for this purpose. Liquid ingredients are added to the vat first
followed by the addition of the dry ingredients. When frozen ingredients are used, they
must be thawed prior to their being added to the mix. Bulk flavorings are not added at
this time; they are added at the time of freezing.
c. Pasteurization of Mix. The same equipment and methods used to
pasteurize other fresh dairy products (milk) are used here, but higher pasteurization
temperatures are required because of the density of the mix. In the vat method, a
temperature of 155F (68C) is maintained for 30 minutes. In the HTST method, the
temperature is 175F (79C) for 25 seconds.
d. Homogenization. This step is necessary to disperse the fat and solids to
produce a smoother mix, to make whipping easier, and to prevent churning of the fat in
the freezer. This is most efficiently done after pasteurization while the mix is hot.
e. Cooling. After homogenization, the mix is cooled in a vat or continuously by
means of a surface cooler or plate cooler to 32 to 40F (0 to 4C). Low temperature
retards bacterial growth.
f. Aging. At one time, it was a common practice to age the pasteurized,
homogenized mixture for 4 to 24 hours prior to freezing. This procedure aided in
freezing and gave the ice cream a better body and texture. However, the modern
methods of using stabilizers and emulsifiers together with the addition of solids-not-fat
have made long aging periods unnecessary.
g. Freezing. Freezing is the process of converting the liquid mix into a
semisolid, frozen, crystalline form. The process includes the incorporation of air into the
product: called overrun. Bulk flavors, fruit, and nuts are added during the freezing
process. The internal temperature of the ice cream is reduced to 21 to 25F (-6 to
h. Packaging. The ice cream may be packaged in bulk directly from the freezer
or it may be packaged in various styles of containers by means of special packaging
machines. The net weight of one gallon of ice cream must be at least 4.5 pounds.
i. Hardening and Storing. Hardening is a continuation of freezing. It may be
accomplished in a hardening tunnel or in a room with temperatures of -20F (-29C) or
lower. Ice cream may be stored for relatively long periods at -10 to-20F (-23 to
1-34. TYPES OF ICE CREAM
There are 10 types of frozen desserts according to Federal Specification
EE-I-116. Most types are subdivided by grade or by class. Although the types are
listed below, the discussion is directed primarily toward regular vanilla ice cream.