type of cream, which depends on the length of time the milk was left to stand). If left for a while, milk
will completely separate out into its two phases. To prevent this occurring during milk storage, milk that
is not to be drunk immediately is usually treated first.
The effect of heating cream
Cream is often added to a sauce to thicken it. Since cream contains a significant amount of fat
droplets, cream can be added to a liquid sauce and the fat from the cream will be redispersed in the
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new larger water phase, reducing the ability of the water molecules to flow, thickening the original
sauce. The fat droplets will be stably incorporated in the water phase due to their surrounding
Milk however is less effective as a thickener due to its much lower fat content (only 4%). However,
since cream itself is an emulsion of fat droplets in water, cream itself contains quite a significant
amount of water, so the resulting sauce thickened with cream will be less thick than if pure fat was
added. Therefore, cream that is intended to thicken a sauce is often first heated to evaporate some of
the water in its water phase, and allow it to thicken the sauce more effectively.
When air is introduced into cream by whipping, a light and airy mousse is obtained, similarly to when
egg whites or hot milk are whisked. However, unlike most mousses, in whipped cream it is not
denatured proteins that function to surround the air bubbles and keep them stably incorporated in the
cream, it is the fat that stabilises a cream mousse. As the cream is whisked, air bubbles are
temporarily incorporated into the cream.
Further whisking will force the fat droplets around, which will cause some of their phospholipids to be
rubbed of the droplet surface. This exposes unprotected fat, which, since it hates to interact with
water, will tend to place themselves in contact with the air bubbles, and gradually these exposed fat
globules form walls around the air bubbles, keeping them in place.