strengthen the network and may cause it to start to squeeze out water.
There is a very fine line between the temperature of thickening and the temperature of lumps forming,
and this transformation may occur very suddenly with only a very slight temperature. Egg- thickened
sauces should thus be heated over a very gentle heat, ideally in a bain marie, where heat is
transferred slowly by the hot liquid, rather than quickly by direct conduction.
Coagulation due to over-heating can be prevented in advance in the following ways:
1) Adding more liquid. In the presence of a large quantity of liquid, the egg proteins are to an extent
“diluted out”, and it is less likely that they will lump together before they have had the chance to
unwind. However, the thickening capacity of egg yolks will also be limited if the original mixture
contains a high amount of liquid.
2) Adding an interfering molecule, like a carbohydrate (such as a small amount of flour). The presence
of these long cumbersome starch molecules make it much harder for the egg yolk proteins to meet
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and lump together before they have unwound, and higher temperatures can be reached before
coagulation occurs and lumps are formed.
3) Stirring constantly. The mixture should be stirred regularly during cooking to both
a) allow a more even distribution of heat, reducing the chances of lumping, which may occur in areas
of the sauce if they are heated more strongly...
of the sauce if they are heated more strongly than the rest of the sauce (such as the part of the sauce
in contact with the pan).
b) stirring constantly further reduces the chances that the egg yolk proteins will find each other and
lump together before they have unwound.
If an egg thickened sauce does start to curdle during heating, the lumps can to some extent be broken
up by agitating the sauce in an electric mixer. Although the lumps of coagulated proteins are still
present (and can be seen clearly under a microscope), they are made small enough that they can not
be seen with the naked eye, and do not produce a noticeable “grainy” taste on eating.