Food Biochemistry and Food Processing

608 Part VI: Fermented Foods

Crystallization of the fat is important to maximize
the yield of the butter and minimize loss of fat into
the buttermilk during the churning process. During
the churning process, air is incorporated into the
cream using dashboards or rotary agitators, con-
tributing to the aggregation of fat globules to form
butter granules. The resulting butter grains may be
washed with water to remove nonfat solids, fol-
lowed by working or kneading the butter grains.
During the working step, a water-in-oil emulsion is
formed as the small water droplets are dispersed into
the fat matrix.
The churning process is probably most critical to
the textural quality of the butter. As air is incorporat-
ed into the cream, the fat globules surround the air
bubbles and coalesce with other fat-coated air bub-
bles to form clumps. These clumps continue to coa-
lesce during the churning process, and the volume of
air bubbles decreases. The proportion of solid fat,
which is influenced by temperature, is critical to the
aggregation of fat clumps to form butter. If the rate
of churning is too fast, the fat globules are less stable
and less likely to coalesce, resulting in a greater loss
of fat into the buttermilk.

BUTTERMILK

Natural buttermilk is a by-product of butter manu-
facture (Fig. 26.3) and is categorized as sweet (non-
fermented) or acidic (fermented). Sweet and acid
buttermilk are obtained from the manufacture of
butter from nonfermented, sweet cream and sour or
cultured cream, respectively. The fat content of nat-
ural buttermilk is approximately 0.4% and consists
primarily of the membrane components of the fat
globules. Because of the high content of unsaturated
fatty acids associated with the membrane lipids, nat-
ural buttermilk has a characteristic flavor and is also
more susceptible to the development of oxidized
off-flavors.
Cultured buttermilk and cultured skim milk are
more frequently produced as alternatives to the tra-
ditional buttermilk (Fig. 26.3). The solids-not-fat and
fat content of cultured buttermilk range from 7.4–
11.4% and 0.25–1.9%, respectively. The homoge-
nized and pasteurized milk with the desired fat con-
tent is inoculated with a 1% starter culture of Lc.
lactisssp. lactisand Lc. lactisbiovar. diacetylactis
and Ln. mesenteroidesssp. cremoris. These bacteria
metabolize citrate to diacetyl to contribute to the

development of “buttery” flavor. Acid is produced

by these bacteria at a relatively slow rate.

SOURCREAM

Sour cream is produced from pasteurized, homoge-

nized cream (20–30% fat) and has a pleasant acidic

taste and buttery aroma (Fig. 26.4). Low-fat sour

cream has a fat content ranging from 10 to 12%.

Following standardization of the milk and cream to

Figure 26.3.Processing scheme for cultured

buttermilk.