Food Lipids: Chemistry, Nutrition, and Biotechnology

Figure 24 Plasticization of margarine. (A) Firm, with yield value of 1000 g/mL and (B)
soft, with yield value of 200 g/mL. (Redrawn from Ref. 67.)
A. Crystallizing
1. Plasticizing
Plasticizing is the most commonly used process for chilling and plasticizing margarines
and shortenings. Votator is one manufacturer’s name for a swept-surface heat
exchanger used to plasticize fat and thus the term votation. Molten fat is pumped
into the first swept-surface heat exchanger known as an A unit, where the fat is
supercooled to 15–25�C in 10–20 seconds, depending on the product. Ammonia or
Freon products are used as the heat exchange media in the exchanger jackets by
means of a direct expansion refrigerant system. Oftentimes 5–25 vol % of nitrogen,
or in some cases air, is injected along with the melted fat and whipped or dispersed
in the crystallized fat. The entrained gas makes shortenings white and may provide
some physical leavening in bakery products.
The supercooled fat is then passed through one or more worker tubes, known
as B units. Here the fat crystals are sheared while the heat of crystallization is
dissipated. The temperature of the fat can rise 5–10�C as a result of the heat of
crystallization. The fat at this point may be sent to a filling unit, or it may be
subjected to a second but special heat exchanger known as a C unit. The final product
will have a temperature of 13–24�C.
Firm table margarine is made with quiescent A units (lacking an internal agitator)
replacing worker B units, whereas working B units are used to produce softer
margarines.
2. Stehling
Stehling is a process that is often used to produce fluid shortenings, which are suspensions
of fine crystals of solid fat in liquid oil. These products are pourable and
pumpable, characteristics that are important to liquid frying shortenings, bread and
cake shortenings, and nondairy products. Stehling is nothing more than stirring the
oil/fat blend (and emulsifiers) after votating for a prolonged period at a precise
temperature, to induce the formation of very small crystals that will remain dispersed
in the liquid oil and not separate during reasonable transporting and storage periods.
B. Postprocessing Tempering
After plasticizing and packaging, shortenings are often moved to tempering rooms
for 2–4 days, where the temperature is controlled at 25–35�C, depending on the
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.