Mayonnaise
Mayonnaise, hollandaise, vinaigrettes and all
their variations are emulsions. An emulsion is
when water and fat come together to make a
creamy thick liquid, generally a sauce. Water
and oil, as the expression goes, don't mix.
However, when liquid fats are slowly
incorporated into watery liquid, the fat
molecules disperse in the liquid and result in a
thick and creamy suspension. This process, fat
slowly whisked into a thin liquid, is repeated
constantly in cooking: oil into vinegar for
vinaigrettes, oil into egg yolks with lemon
juice for mayonnaises and hollandaises, and
chilled butter into wine for beurre blanc.
Start with the liquid (usually an acid like
lemon juice, vinegar or wine) and the seasonings
(herbs, mustards, salt, pepper, etc.) in a bowl.
Blend the liquid and the flavorings with a
whisk. Make sure that the bowl is stabilized
with a dishtowel underneath it so you can use
one hand to whisk and the other to pour while
making the emulsion. Then, in a thin stream,
while whisking, start drizzling in the fat
(usually melted butter or oil). The mixture will
at first be cloudy, then it will thicken. If it
is not thickening, stop pouring in oil. Whisk in
one corner of the mixture, coaxing part of the
oil and acid into an emulsion. Then widen the
amount being whisked to incorporate the rest of
the oil.
When an emulsion breaks down, the fat and
liquid separate, and looks curdled. The standard
kitchen phrase for this is that "the sauce is
broken." Two key techniques that almost always
ensure a successful emulsion are, first, a
stable temperature, making the emulsion at
neither too hot nor cold a temperature, and
second, always add the fat slowly into the
watery liquid. Certain foods help to make
tighter, thicker emulsions of fat and water, for
example mustard, cream and egg yolks in
vinaigrettes.
