denatured milk proteins will be concentrated here, and will be sufficiently concentrated that they may
coagulate and form a skin. Skin formation can be prevented by reducing water evaporation – most
conveniently achieved by adding a lid. Although the skin is perceived as unappetizing, removing the
skin removes the majority of the milks proteins, greatly reducing the nutritional value of the milk.
Similarly, water at the bottom of the pan, which is in direct contact with the heat from the stove, will
evaporate very quickly, concentrating denatured proteins here which may burn with the high heat.
Dehydration here can be prevented by adding a bit of water to the bottom surface of the pan before
adding the milk, to increase the concentration of water here.
Cold milk cannot be whipped like cream to form a stable foam. This is because cream is much more
concentrated in fat than milk so the air bubbles can be coated more thoroughly with the fat droplets.
Secondly, cream contains lower water content than milk, so has a much greater viscosity/thickness,
further stabilising the mousse.
The stabilising effect provided by the phosholipid membrane of fat globules is not enough to keep the
water and fat phases from separating over time. The fat droplets are large enough that they will
eventually find each other and combine or “coalesce”, overcoming the stabilising effect from the
phospholipids and these large droplets will rise to the surface of the liquid, due to their lower density,
causing a separation in the phases.
This process is helped by a small family of soluble proteins who attach themselves to the large fat
droplets and help their association. This causes a fat rich layer to be formed near the surface of the
milk. This can be beneficial and is how cream is produced.
Cream therefore has a very similar structure to milk - they only differ in its elevated fat content (milk
only contains about 7% fat, whereas cream contains between 18% and 47% fat, depending on the