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SOUFFLÉS have a reputation for being perilous, but they aren’t nearly as challenging as many people will have you believe. In fact, as long as you have a mixture full of air bubbles, the laws of physics dictate that it must rise when it is heated.

The relevant principle is described by Charles’s law, named after the French scientist Jacques Charles, who was also a pioneer of balloon flight. It states that the volume of a gas is proportional to its temperature.

That means the bubbles in a soufflé mixture expand when they are heated, but this only accounts for about a quarter of the rise. Heating also causes water in the mixture to evaporate, which adds to the amount of gas in the bubbles.

These two processes should reliably ensure that a soufflé rises, and the hotter the oven, the quicker and bigger the rise. The flip side – and the bane of many a dinner-party chef – is that a soufflé will inevitably start to sink as soon as it comes out of the oven. The only way around this is to serve it straight away. A fallen soufflé will rise again if returned to the oven, although not to its original height.

The structure that holds the gases comes from egg whites that have been whisked until stiff, producing a stable foam. This is the result of globular proteins in the egg unfolding when beaten, then bonding together to create a rigid framework that stabilises the bubbles. Aquafaba, the liquid drained from a tin of chickpeas, can be used as a vegan substitute as it contains some of the same proteins found in eggs. Sugar and acid help to increase the stability of the foam.

Hervé This, author of Molecular Gastronomy, recommends placing a soufflé at the bottom of the oven, so it is heated directly from below. If evaporation starts at the bottom of the ramekin, the bubbles lift the whole soufflé upwards. He also suggests putting the soufflé under a grill (broiler to North Americans) to seal the surface before baking it. This prevents bubbles at the top from bursting, thereby keeping more of the gas inside. In my experience, however, you can still get an impressive rise without doing this, so you might want to skip it to save time.

To make four banana soufflés, mash two ripe bananas with two egg yolks and a pinch of salt. In a separate bowl, whisk four egg whites with a tablespoon of lemon juice. When soft peaks form, gradually add 60 grams of sugar while continuing to whisk until the foam is stiff. Add a quarter of the foam to the banana mixture and stir vigorously to lighten it. Then slowly and gently fold in the rest of the foam with a spatula.

Spoon the mixture into four buttered ramekins and bake at 200°C for about 15 minutes, or until well risen and brown on top. Serve immediately with sugared nuts, caramel sauce or ice cream. Or why not add all three?

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