sources will tend to bind to the hydrophobic parts of the protein as it is denatured, reducing the
number of available hydrophobic groups that can surround and support the air bubbles.
However, once a stable mousse has been formed, the fat source may be added (and often is
when preparing cakes or souffles). Egg whites are whisked in the absence of egg yolks or else
the hydrophobic parts of the lecithin molecules will tend to link to the hydrophobic groups of
the denatured egg proteins, preventing these groups from forming the network stabilising the
7. Sugar is often added to egg whites to make meringues. Sugar tends to destabilise the
formation of the denatured protein network, so should be added after the egg whites have
been whisked. As well as generally “diluting” the numbers of proteins, the sugar molecules
themselves surround the protein molecules, preventing them from binding with each other so
easily. This especially pronounced with icing sugar, where sugar particles are even smaller, so
are able to surround the protein molecules even more tightly. Sugar also increases the
viscosity of the liquid part of foams, limiting the “creaming” of air bubbles.
Use of eggs in cooking: how to cook egg white foams (e.g. meringues and souffles)
Meringues are prepared by whisking egg whites, adding sugar, and cooking the resulting mixture.
Souffles are slightly more complicated to prepare - whisked egg whites are added to a flavoursome
thick base, and the resulting mixture is cooked. When a souffle or a meringue is placed in the oven, it
III/I - 7 (of 9)
Why does it swell?
When a mixture containing whisked egg whites is placed in a hot oven, the mixture will rise. Heating
causes the water in the mixture to evaporate (one gram of water makes about one litre of vapour) and
also it causes gases incorporated in the egg whites to expand.
Because the protein network surrounding the gas bubbles is still fairly delicate, the meringue will swell
and the souffle will rise.
Calculations have shown that gas expansion alone is not sufficient to account for the significant