Folding in Baking: How to Fold Without Losing the Air
Folding is a gentle mixing technique used to combine a light, airy mixture, such as whipped egg whites or whipped cream, with a heavier one, such as a cake batter, custard base or melted chocolate, while keeping as much trapped air as possible. It's essential for soufflés, chiffon and angel food cakes, mousses and macarons.
Why the air matters
Whipped egg whites and cream are foams: millions of tiny air bubbles held in place by a thin film. In egg whites, the film is made of denatured proteins that have unfolded and linked together at the bubble surfaces. In whipped cream, it's partly clumped fat droplets.
Those bubbles are the leavening. In the oven, trapped air expands as it heats (gas expands about 27% between room temperature and 100 °C / 212 °F), and water in the batter turns to steam and pushes into the existing bubbles. A soufflé or sponge rises only as much as its bubbles allow. Burst them during mixing and no amount of baking powder fixes it.
Bubbles break when they're sheared (stirred or beaten hard), squashed under heavy batter, or touched by fat such as egg yolk or butter, which disrupts the protein film.
How to fold
- Lighten the base. Stir about a quarter to a third of the foam into the heavy mixture. You'll lose some air in this portion, and that's fine. It makes the base looser and closer in density to the foam.
- Add the rest of the foam in one or two additions.
- Cut down through the centre with the edge of a large spatula.
- Sweep across the bottom of the bowl toward you.
- Lift and turn the spatula up the side and over the top, bringing the bottom mixture up over the foam.
- Rotate the bowl a quarter turn and repeat.
- Stop early. When only a few faint streaks remain, you're done. They'll disappear as you pour.
For dry ingredients like flour or cocoa folded into a foam (génoise, angel food cake), sift them over the surface in two or three batches so they don't land in heavy clumps.
Temperature counts
When folding whipped cream into melted chocolate for a mousse, the chocolate should be warm, not hot, around 40 °C / 105 °F. Too hot and it melts the cream's fat structure; too cold and the chocolate sets into hard flecks the moment it meets the cold cream. Lightening with a small amount first evens out the temperature, too.
Other meanings of "fold"
- Stretch and fold: pulling bread dough up and over itself in the bowl to build gluten without kneading.
- Letter fold or lamination: folding butter-layered dough in thirds for croissants and puff pastry. See laminated dough.
Common mistakes
- Using a small spoon and stirring in circles.
- Dumping all the foam on a stiff base without lightening it.
- Overfolding to remove every last streak.
- Letting the batter sit. Get folded batters into the oven right away; foams slowly drain and collapse.
Questions
What is the difference between folding and stirring?
Stirring moves a spoon in circles through the mixture and shears air bubbles. Folding cuts down through the centre, sweeps along the bottom and lifts the mixture up and over itself, mixing with as little pressure on the bubbles as possible.
What tool is best for folding?
A large, wide, flexible silicone spatula. Its broad blade moves more mixture with fewer strokes. For génoise and other sponge batters, some bakers fold with a large balloon whisk, which cuts through without crushing the foam.
Why did my batter deflate when I folded it?
Usually from overmixing, adding the foam to a base that was too heavy without lightening it first, or using a foam that was underwhipped or overwhipped and already unstable. Stop folding as soon as only a few streaks remain.
Should you fold egg whites into the batter or batter into the whites?
Stir about a quarter of the whites into the heavy base first to loosen it, then gently fold the lightened base into the remaining whites, or the whites into the base. Either works once the densities are closer.