Why is it best to use fresh eggs at room temperature when making a sponge cake?

When making a sponge cake or sponge roll, eggs are whisked with sugar to increase their volume and incorporate air, creating the characteristic fine crumb and light texture of these wonderful cakes. Fresh, room temperature eggs are best in sponge making, but why?

Fresh egg whites are slightly more acidic than older egg whites. As an egg ages, carbon dioxide escapes through the shell, causing the white to become more alkaline and thinner as its protein structure changes.

When you whisk eggs, you are denaturing their proteins, causing them to unfold and form a network around tiny air bubbles, creating a foam. Fresh egg whites tend to produce a more stable foam than older whites, but they can take a little longer to whip to the desired volume. Using room-temperature eggs helps compensate for this, as they generally incorporate air more readily and reach the desired volume more quickly than chilled eggs.

So, with fresh eggs at room temperature, you get the best of both worlds: a stable foam that can be whipped efficiently. When making recipes that rely on whisked eggs or egg whites, including sponges cakes and rolls, soufflés and meringues, choose the freshest eggs you can and bring them to room temperature before you begin.