• Properly folding egg whites is crucial to fluffy cakes and mousses.rasberry mousse cake image by MAXFX from Fotolia.com
  
  Folding is a gentle mixing method, typically used to combine an airy or fragile mixture such as whipped egg whites into a denser mixture like cake batter. Folding helps to maintain the volume and trapped air bubbles that have been whipped into the egg whites and ensure that your soufflé, cake or mousse is light and fluffy.
  
  

Basic Technique

• Make sure the denser batter is thoroughly mixed and in a large bowl. Stir a large spoonful of whipped egg whites into the batter, and stir gently with a whisk. Next, scoop half of the remaining egg whites onto the batter. Using a rubber spatula, cut through the center of the batter to the bottom of the bowl, and lift some of the batter up and on top of the egg whites. Rotate the bowl a quarter of a turn, and repeat. Continue until only a few slight streaks of white are visible, then scoop in the remaining egg whites. Continue the folding movement until all egg whites have been incorporated into the batter.
  
  

Tools

• Most commonly, a rubber or silicone spatula or spoon is used. However, some people choose to use a whisk or metal knife to gently incorporate the beaten egg whites. Make sure the chosen tool is light enough to be easy controlled so folding can be done gently and efficiently.
  
  

Tips and Tricks

• Don't risk deflating the air bubbles in the egg whites by being too thorough with the incorporation---slight streaks of white foam in the batter are fine. Also, never add the heavier mixture to the egg whites, which will deflate all of the trapped air bubbles and ruin the consistency of the final product.