Step by step recipe:

1. 5 min.
   They should be beaten at high speed.
   
   If they are for savoury or neutral preparations (i.e. without sugar), add a teaspoon of lemon juice before starting to beat to prevent them "going grainy" which can happen with very fresh egg whites.
   
   If they are for sweet preparations (for meringues for example), incorporate 2 tablespoons of caster sugar from the total sugar you plan to add, halfway through beating, which makes it much easier to beat and to incorporate the remaining sugar.
2. 
   Beating egg whites incorporates air, which creates a foam made up of ever smaller bubbles of air and drops of white (albumen + water), see the microscope photo on right.
   
   This fact give us some rules for egg whites:

   • Fresh egg whites give better results that old ones, because they contain more water.
   • If you add water or a liquid which contains some (fruit juice, ...) to egg whites to be beaten, you will have a greater volume of foam.
   • Fat is the enemy when beating egg whites, because it obstructs or prevents the formation of foam, so it's necessary to be sure that the egg whites contain no traces of yolk (not a drop), and that the container that you're going to use is completely clean (be particularly careful with plastic bowls).