Yogurt. Yogurt is a gelled milk pro

Yogurt. Yogurt is a gelled milk product by the isoelectric
precipitation of milk proteins caused by lowering
the pH of the milk to∼4.6. For yogurt manufacture
the yogurt milk can be formulated in a number
of ways. Once the desired formulation is achieved,
the milk is homogenized and heat-treated to destroy
undesirable microorganisms and modify the physicochemical
properties of milk proteins. Typically, highheat
treatment, such as 85◦C for 30 minutes or 95◦C
for 5 minutes are used. Many of the properties of yogurt
are controlled by the heating step. A relatively
high-heat treatment is required as a key requirement
in that the whey proteins of the milk are denatured.
These proteins are then precipitated with the caseins
when the pH is lowered by the action of the added
cultures. For optimal yogurt performance (highest
viscosity, resistance to whey drainage) at least 90%
of the whey proteins should be denatured. Although
a high-heat treatment is applied, it is essential that
there is no precipitation or excessive thickening of
the yogurt milk during heating as this will give rise
to a product with poor characteristics. In general, increasing
the whey protein content of the yogurt milk
creates yogurt with a firmer texture and a greater resistance
to whey drainage than yogurt made from
milk with a normal ratio of casein to whey proteins.