When coffee milk does not want to froth, these might be the
reasons:
1. Proteins in milk
The protein in milk, especially the whey-proteins, is largely
responsible for the foaming capacity in milk. These proteins
form a film on the surface of the air bubbles in the foam.
Heating milk above 60°C causes the proteins to be denatured and
it is more efficient in coating and stabilizing the air bubbles.
UHT milk froths better than pasteurized milk, more proteins are
denatured. Changes in season and what cows eat can negatively
affect proteins in milk, and thus negatively effect foaming.
2. Homogenization
Homogenization improves the process of steam frothing
3. Milk fat
In general the lower the milk fat, the more foam will be formed.
Skim milk will give the greatest volume of foam. This equation
changes slowly when milk fat is raised above 5%. Above this
value higher fat will give more foam. Breakdown of fat or
lipolysis will negatively affect foaming of milk. Lipolysis
generally occurs before the pasteurization of milk and is caused
by the enzyme lipase. Lipolyses producers free fatty acids. Free
fatty acids are surface-active agents, which depress the foaming
capacity in milk. Lipolysis can occur spontaneously in milk and
is aggravated by agitation. This will occur when the cow's level
of nutrition is low and when she is late in lactation. This
occurs in herds and regions due to feed available. This can
happen during a period of adverse weather and when cows are
seasonally calved. Lipolysis due to agitation commonly occurs at
farm when air leaks into teat cluster and air and warm milk are
vigorously mixed in milking equipment. Also occurs in factory
when air is incorporated when raw milk is pumped. Lipolysis will
also occur if raw milk is mixed with pasteurized / homogenized
milk
4. Milk temperature
Low temperature makes milk more receptive to taking in of air
5. Mastitis
Mastitis is a infection of the udder and somatic sell counts are
a indicator of the severity of the infection. Foam capacity of
milk decreases as somatic sell counts increase
6. Milk solids
Milk solids have a small effect on the foaming capacity of milk.
Adding solids e.g. skim milk powder can increase foaming
capacity to a small degree. Adding water has little effect on
foaming of milk.
7. Freshness
Refrigerated storage of pasteurized milk up to three days does
not affect foaming ability.
About the author:
Leon the Milkman is the owner of www.LeontheMilkman.com and
offers a free Dairy Dictionary at www.dairy-info.org.
