452 Chapter 17
channels and in grocery stores is 4 ° C to 7 ° C
(39 ° F to 45 ° F), a loss of one log cycle in
culture viability is expected between manu-
facture and consumption. Therefore, at the
time of consumption, yogurt should deliver
at least 10 million CFU of live yogurt
organisms/g of the product.Sour Cream
Sour or cultured cream is manufactured by
ripening pasteurized cream of 18% fat with
mesophilic lactic acid culture ( Lactococcus
lactis subsp. lactis/cremoris/diacetylactis )
and aroma - producing Leuconostoc cremoris.
The culture used is identical to that used in
cultured buttermilk, but in consistency sour
cream is an acid gel with a butter - like aro-
matic fl avor. Sour cream is used as a topping
on vegetables, baked potatoes, salads, fruit,
fi sh, and meats, and in soups and as a fi lling
in cakes. It is an integral component of
Mexican cuisine. Sour cream can be dehy-
drated by spray drying and used as an ingre-
dient wherever its fl avor is needed.
The composition of sour cream is 18.5%
milk fat, 7.1% MSNF, 0.4% stabilizer, and
26% total solids. It is considered desirable to
supplement cream (which contains 6.8%
MSNF) with nonfat solids to increase the vis-
cosity of the fi nished product. The formula-
tion consists of 50.9% skim milk, 48.6%
cream (40% fat), and 0.5% stabilizer. It is
customary to add a small quantity of rennet.
More fl avor can be generated after culturing
if 0.15% to 0.2% sodium citrate is incorpo-
rated in the sour cream mix.
Sour cream is manufactured by blending
the stabilizer in a portion of approximately
10% skim milk through a powder funnel
(Figure 17.7 ). The cream is then added along
with the remainder of skim milk to fl ush
the line. The mix is heat treated at 87.8 ° C
(190 ° F) for 3 to 5 minutes, homogenized
at 71.1 ° C (160 ° F) and 17.2 MPa (2,500 psi)
(single stage), cooled to 22.2 ° C (72 ° F), and
pumped to a cone vat. In general, sour creamshelf life. A recent trend is to include fructo -
oligosaccharide prebiotics, such as inulin,
and to fortify with a signifi cant daily require-
ment of most vitamins and minerals.
Kefi r is another fermented drink obtained
by use of Kefi r culture. It has a distinctive
fl avor, and most kefi r products in the United
States are sweetened with sugar and fl avored
with fruit juices.
Quality Control
For refrigerated yogurt and yogurt beverages,
most spoilage organisms are yeasts and
molds which are highly tolerant to low pH
and can grow under refrigeration tempera-
tures. If yeast contamination is not controlled,
fungal growth manifests within two weeks of
manufacture. To ensure maximum shelf life,
several manufacturers use potassium sorbate
to control the growth of yeasts and molds in
the product.
Quality control checks (spot checking)
should be performed on fruit preparations
and fl avorings to ascertain sterility and to
eliminate yeast and mold entry via fruit prep-
aration. Refrigerated storage of the fruit fl a-
vorings is recommended.
Quality control programs for yogurt
include control of product viscosity, pH,
fl avor, body and texture, color, fermentation
process, and composition. Product standards
of fats, solids, viscosity, pH (or titratable
acidity), and organoleptic characteristics
should be checked regularly. Wheying off or
appearance of a watery layer on the surface
of yogurt is undesirable and can be controlled
by judicious selection of effective stabilizers
and proper processing conditions.
Yogurt products enjoy an image of a
health - promoting food. The type of cultures
and their viability as well as active status are
important attributes from the consumer
standpoint. Generally, at the time of manu-
facture, yogurt should contain not less than
100 million CFU/g. Assuming that the storage
temperature of yogurt through distribution