Milk skin

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Milk skin (regionally also called Schmand or Schmant , Flähme (old Bohemian) , Flott , Pelle or Flotte ) is a film that is created when milk is heated . Skin formation during the cooking process is a complex process: It depends on various factors such as the heating and cooling conditions. Other important influencing variables are fat content and degree of homogenization .

When the water evaporates, a milk skin forms on the surface of heated milk, which consists of around 70% fats and around 20-25% proteins. Of the proteins involved, the main proportion is probably denatured lactoglobulin , but the somewhat less heat-sensitive albumin is also likely to be present in the skin in a smaller proportion. According to more recent findings, however, casein probably plays a subordinate role. So far, however, there are no extensive studies.

If milk is heated to over 75  degrees Celsius , the molecular clusters of the proteins albumin and globulin unravel ( denaturing ) and then stick together ( aggregation ). This is how a thin, net-like structure is formed: the milk skin. Since the skin is lighter than water, it always floats on the surface. A full-fat, non-homogenized raw milk forms a full-bodied and thicker skin when cooked than homogenized milk. When the rising water vapor builds up under the milk skin and raises it, the typical reaction of the milk boiling over occurs.

Milk skin is perceived by some people as unsavory or even nauseating. It can be avoided by careful, not too strong heating and simultaneous whipping or frothing of the milk, e.g. B. with a whisk, which prevents the underlying layer formation. In addition, stirring the milk prevents this process, as air gets into the milk, which is trapped by the coagulating proteins. In this way, milk foam forms instead of the milk skin.

In molecular gastronomy milk skin is also used as an ingredient. Ferran Adrià uses it to prepare crepes or ravioli, for example .

See also

Individual evidence

  1. a b Which whey proteins are denatured when the milk skins? Agroscope, Federal Office for Agriculture, Switzerland ( Memento from July 23, 2012 in the web archive ).
  2. Friese / Hettgen: Chemistry in the household: Casein - a glue made from milk. Institute for Didactics of Chemistry, Uni Münster, SS 2005, p. 6, accessed on August 10, 2009 (PDF; 605 kB).
  3. Script experiments on animals - Experiment 68: Detection of albumin and globulin. Subject didactics, Weihenstephan Science Center, TU Munich, p. 9 ( Memento from August 25, 2005 in the Internet Archive ).
  4. Broadcast header : Why is milk boiling over? WDR, September 14, 2008 ( Memento from February 12, 2013 in the web archive ).
  5. Why does milk have a skin? Meine Milch portal , Dairy Industry Association ( Memento from August 6, 2010 in the Internet Archive ).
  6. Anna Burghardt: Understanding of crap: waste in the top kitchen. Die Presse , October 20, 2010, accessed November 30, 2010.
  7. Wolfgang Lechner: A fish as a wine cork. Zeit Online , July 24, 2007, accessed November 30, 2010.