For those interested in the science behind beating egg whites
Egg white is about 90% water and 10% protein
Beating egg whites triggers the denaturation of protein: long-chain amino acids unfurl from a somewhat spherical shape. This exposes various amino acids that are either hydrophilic (absorbs water on a molecular level) or hydrophobic (repels water on a molecular level).
When whipped correctly, the hydrophilic amino acids will form what are called ionic bonds, created by electrically charged molecules that bind to water molecules.
Ionic bonds are the best bonds as they create a voluminous, silky, and moist meringue.
Water molecules easily bond to each other and form a film. But as more and more air is beaten into the egg whites it stretches the water film, forcing the molecules farther apart from each other.
If too much air is whipped into the egg whites, it forces the water molecules out of the network of amino acids (proteins), water, and air bubbles.
Disulfide bonds are bonds between the amino acids that have sulfurs. When too many water molecules are squeezed out of the network and these really tight disulfide bonds form between the sulfur amino acids form the result is dry egg whites with gritty tiny white specks.
So two types of bonds can occur in whipped egg whites:
ionic bonds (perfectly beaten egg whites)
- disulfide bonds (over-beaten egg whites)
The ionic bonds are desirable for meringue, but they are NOT stable.
To stabilize the ionic bond you must do three things:
1. add an acid
2. add sugar at the correct time and slowly
3. gradually beat egg whites from low speed to high speed
Acid: recipes instruct bakers to add an acid, but never explain why. An acid, like cream of tartar, is potassium hydrogen tartrate. It’s the hydrogen that is important. A hydrogen atom contains a single positively charged proton and a negatively charged electron. Because it has a negatively charged electron, it can keep protein from binding with other proteins. So disulfide bonds are less likely to occur.
Sugar: Adding sugar to whipped eggs too soon will interfere with the protein denaturalization process (sugar molecules can get in the way as the hydrophilic amino acids bind with water molecules). The sugar and water molecules also bind, adding more stability to the egg whites by keeping the water molecules from being forced out. If the sugar is dumped in or added too fast it will not disperse the sugar evenly throughout the egg whites to build a stable network of water and sugar molecule bonds.