What is the purpose of aging egg whites in Macaron preparation?

Aging egg whites is a crucial step in macaron preparation, and the main purpose is to improve stability and volume. When egg whites are aged, typically by allowing them to sit uncovered in the refrigerator for a day or so, several beneficial changes occur. The aging process helps to reduce the moisture content in the egg whites, which leads to a more stable foam when they are whipped. This stability is essential for achieving the characteristic texture and structure of macarons.

By whipping aged egg whites, one can achieve a greater volume, resulting in a meringue that holds its shape better when piped onto baking sheets. The improved stability of the meringue also contributes to the overall integrity of the macaron shells during baking, helping them develop their signature "feet" and preventing deflation. These factors are all critical to the success of the final product, making the aging of egg whites a pivotal step in creating perfect macarons.