Light and airy beaten egg whites are the secret to a fluffy frittata and a delicious meringue-topped dessert.

What Happens?
Beating egg whites increases their volume and affects their consistency; the longer they're beaten, the stiffer they become.

Separating the Eggs
Even a drop of fat will decrease volume, so be careful not to let any yolk fall into the bowl. Eggs are easiest to separate when they are cold, but bring the separated egg whites to room temperature before beating them.

The Right Bowl
Stainless-steel and copper bowls yield the best results. Avoid plastic, which can retain traces of fat even when washed.

Storing
Refrigerate unbeaten whites, tightly covered for up to four days, or freeze (in ice-cube trays, then transfer to a freezer bag), up to six months (thaw overnight in the refrigerator).

Peaks and Techniques
Soft Peak
At this stage, whites appear thickened but slightly droopy when whisk is right side up. This is the time to gradually add sugar for meringues.

Stiff Peak
At this next stage, whites form a peak that holds its shape when whisk is right side up. Whites also stay put when the bowl is turned upside down.

Overbeaten
Beaten past stiff peaks, whites begin to look curdled and can't be used. To correct, beat in additional whites one at a time until peaks form again.

Folding
To combine whites with heavier components, gently fold them in with a rubber spatula: Scoop down in center and up at edge in a circular motion.

Egg-White Basics
These simple steps can be followed for most recipes that use beaten egg whites:

1. With a paper towel, rub a mixing bowl and a whisk with a small amount of lemon juice or vinegar to remove any traces of fat.

2. Separate one egg at a time by letting the white run through fingers into a small bowl. (Reserve yolk for another use.)

3. Transfer each white from small bowl to mixing bowl before separating the next (so if yolk leaks during separation, you won't taint all the whites).

4. Beat whites with a pinch of salt until desired stage is reached.