To beat in cooking is to mix something up with great zeal and abandon.
Beating both mixes all the ingredients together evenly, and introduces air, to help a food item either develop body (such as whipped cream and meringue) or to help it rise when baked (such as cakes.)
A variety of implements can be used to Beat food: manual implements such as a fork, spoon, manual egg-beater or whisk (though when it’s done with a whisk, it’s often referred to as “whisking.”) The spoons can be metal, wood or plastic. You can also Beat with electrical devices such as a stand or hand electric mixer, food processor or blender.
One minute of beating with an eclectic mixer equals one hundred “goes” at it by hand.
Egg proteins are made up of hydrophilic and hydrophobic amino acids. “Hydrophilic” means “likes water”; “hydrophobic” means “doesn’t like water.”
As air bubbles get introduced into egg white by beating the white, egg proteins rearrange themselves so that their amino acids that don’t like water will go toward the air bubbles. After they re-arrange themselves, the proteins bond together again in their new arrangement, which creates a structure that will hold the air in. This both creates body (as in the case with meringue), and creates pockets of captured air which will expand when heated, which causes cakes to rise.