What the air is doing
Whipped egg white, whipped cream and creamed butter and sugar all hold air in a network of tiny bubbles. In a soufflé, a mousse or a sponge, those bubbles are the leavening — they expand in the oven and hold the structure until it sets.
Stirring shears those bubbles and they collapse. The mixture visibly loses volume, goes looser and wetter, and bakes flat.
Folding moves the mixtures through each other with as few strokes as possible and without shearing. It is slower to combine and it keeps the air, which is the trade you want.
The motion
A large flexible spatula, a wide bowl, and as few strokes as possible.
- First, slacken the heavy mixture. Stir a spoonful of the light mixture into it properly — sacrificing that spoonful makes the rest fold in far more easily and costs almost nothing.
- Add the remaining light mixture on top. Do not tip it into the middle.
- Cut down through the centre with the edge of the spatula to the bottom of the bowl.
- Sweep along the base, up the far side, and fold the mixture from the bottom over the top.
- Turn the bowl a quarter turn and repeat.
- Stop the moment you no longer see streaks. A few faint streaks are better than a deflated bowl.
The rules that matter
- Light into heavy
- Always. Adding the heavy mixture to the light one crushes it immediately.
- Slacken first
- A spoonful of the light mixture stirred into the heavy one makes the rest fold in with far fewer strokes.
- In stages
- Two or three additions rather than all at once, particularly for a stiff base.
- A wide bowl
- A narrow one forces small strokes and more of them.
- A spatula, not a spoon
- The flexible edge cuts through cleanly and scrapes the base.
- Stop early
- Slightly under-mixed beats deflated. Streaks disappear in the oven; air does not come back.
Where it applies
- Egg whites into a soufflé base, a mousse or a sponge batter.
- Whipped cream into a mousse, a fool or a cheesecake filling.
- Flour into a whisked sponge, sifted over the surface and folded rather than beaten.
- Fruit, chocolate chips or nuts into a batter at the very end.
- Meringue into a pavlova base, or into a cake batter for a light finish.
- Not for bread dough, which wants exactly the opposite treatment.
- Not for a creamed cake batter, where beating is how the air got in.
Common questions
Why not just stir it?
Stirring shears the air bubbles and the mixture collapses. Folding keeps them.
Light into heavy or heavy into light?
Light into heavy, always, and slacken the heavy mixture with a spoonful first.
How do I know when to stop?
When the streaks have almost gone. A few faint ones are better than an over-folded, deflated bowl.
What if I over-fold it?
The mixture goes loose and wet and will bake flat. It cannot be re-aerated.
Spatula or spoon?
A wide flexible spatula. It cuts cleanly and scrapes the base of the bowl.
Try this next
- Whisking how the air got in
- Aeration the science of the foam
- Chocolate mousse where it matters most
- Over-whipped cream the upstream fault