<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (October 2014) (Learn how and when to remove this template message) </Td> </Tr> <P> Milk skin or lactoderm refers to a sticky film of protein that forms on top of milk and milk - containing liquids (such as hot chocolate and some soups). Milk film can be produced both through conventional boiling and by microwaving the liquid . It is caused by the denaturation of proteins such as beta - lactoglobulin (whey protein). </P> <P> When milk is boiled, soluble milk proteins are denatured and then coagulate with milk's fat and form a sticky film across the top of the liquid, which then dries by evaporation . The layer does not need to be discarded and can be consumed, as protein's nutritional value is unaffected by the denaturation process . Milk film is often considered to be desirable and is used in several recipes for various foods . </P> <P> In France, a type of rice pudding called teurgoule employs an extreme version of lactoderm where the milk - containing dish is left to cook for many hours . </P>

Why does a layer form on hot milk
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