tend to join together to from a continuous network, and the milk will solidify, or “curdle”.
Furthermore, the denatured casein micelles are no longer able to prevent the denatured lactoglobulin
from coagulating, so heating milk in acid conditions will cause significant curdling. For example, if
lemon juice or vinegar are added to milk, small white particles will appear in the milk. These are due to
the casein proteins coagulating. If this mixture is then heated, the lactoglobulin proteins will also
coagulate, and the white particles become bigger and more visible as they stick together.
Making yoghurt and cheese
When bacteria contaminate milk, the bacteria degrade the lactose sugar present in the milk to produce
an acid called lactic acid. The increase in acidity will cause the casein proteins to coagulate.
Depending on the type of bacteria, this will either be desirable or undesirable. When bad bacteria
contaminate milk, the milk spoils.
When other “good” bacteria are added milk to milk to coagulate the proteins, yoghurt and cheese are
produced. The lactic acid produced by the special bacteria denatures and coagulates the milk
III/VIII - 4 (of 5)
proteins, and the coagulated casein network can trap within it the water and the fatty material, giving
cheese its solid form. Soft cheeses have a fairly high water content (50-75%), whereas hard cheeses
have a lower water content. When cheeses are heated, the network of coagulated proteins becomes
stronger and tighter, and eventually the liquid “trapped” within is forced out, and the cheese will
Cheese, like cream, contains a high fat content (so a large amount of fatty acids), so theoretically it
should be able to stabilize a mousse in the same way that cream does. Cheese actually has a higher
fat content than butter, so to achieve a mousse like with cream a little extra liquid will need to be
added to the cheese mixture. If some wine is placed in a pan with a little cheese (for example
roquefort, reblochon, or goats cheese), the mixture can be slowly heated to obtain a smooth, thick and