Soufflés owe their delicate, puffy texture to the air trapped in whipped egg whites. As the air heats in the oven, it expands, causing the soufflé to rise. The key to achieving the best rise lies in proper folding, a technique for mixing the egg whites with the rest of the soufflé ingredients with a minimum loss of air. Folding starts with stirring about one-third of the whipped whites into the base ingredients. This step sacrifices some of the air, but it lightens the base, making it easier to fold in the rest of the whites. If you’re working with a large amount of whites, you may need to fold in the remaining whites in two or more batches.