Here’s a perfect example of new science knowledge that brought about a better and improved soufflé based on a viscous preparation. It used to be thought that soufflés rose as the air bubbles in the egg whites grew bigger as they became warmer. However, Hervé measured the temperature and pressure inside a soufflé and calculated that the bubbles can swell by 20 per cent at the most, whereas soufflés double in volume.
In fact, the soufflé rises as water from the milk and yolks evaporates, and rises to the top of the soufflé, pushing the layers of mixture upwards. This means that heating the container from the bottom produces the best results. He has also found that the stiffer the egg whites, the more the soufflé rises. The firmer egg whites have a greater volume to begin with, but the firmness of the foam also prevents the bubbles from passing quickly through the soufflé and escaping; slowly rising bubbles are better at pushing up the layers of mixture.