Ask Peter: Egg whites
Can you explain why some recipes call for stiffly beaten egg whites and some for soft and foamy ones — I would have thought thatstiff egg whites would always be best as they would hold up better?
I’m sure there’s an actual chemical or physics-related explanation for this, but here’s how I think it works, in layman’s terms. (Apologies to any science teacher I have had if this is completely wrong.) Egg whites contain protein and liquids among other things and protein is what gives food strength — it can form solid “walls” around liquid or air-filled cells. Protein that is cooked gets even firmer, although heat applied to food can also “set” the inside of the cells and as cell walls are thin, they can sometimes collapse due to a heavy filling.
When you beat egg white, you are whipping air in, which starts to form bubbles that are trapped by the stretched egg white “cell walls”. The egg white begins to wrap itself around the bubbles and as you keep beating and forming more and more bubbles, the egg white “cell walls” begin to get thinner as they are stretched more and more.
When liquid is heated up it expands. This means that if the egg whites are really stiff when you fold them into a cake they will simply burst when baked as they are thin and have lost all their elasticity. Egg whites that have been beaten to “soft peaks” are less likely to collapse when baked. Having said that, if the whites are insufficiently beaten in the first place they won’t rise or hold their shape as the air bubbles are too large and therefore too full of liquid (which is heavier than air, and they will also collapse).
So there is an actual reason why some recipes benefit from one style over the other. Frozen parfaits can be made successfully with firmer beaten whites. This is simply because they won’t be baked and therefore won’t expand any further as they’re frozen instead.
Sometimes it can be hard to fold stiffly beaten whites into a mixture, so what I do is this. Beat the whites to medium peaks then roughly fold a quarter into your mixture. By roughly I mean you can gently whisk them in — you needn’t be too delicate. Then beat the remaining three-quarters into firm peaks and fold these in, somewhat more delicately. The initial amount you’ll have folded in will have “tempered” the mixture and will make the remainder easier to mix in.
Italian meringue is altogether different — it’s a meringue that is cooked as it is whipped, and is the basis of many frozen desserts such as fruit parfaits and also the meringue that works well on a baked alaska. To make it, boil 500g caster sugar with 150ml water and cook until it reaches 115C on a sugar thermometer— around 4-5 minutes of rapid boiling. A minute before it’s ready, beat 5 egg whites to soft peaks on full speed.
Reduce the beater speed to 75 per cent and slowly but steadily pour the boiling sugar syrup over the whites. Increase the speed to full again. Continue beating the meringue until it has cooled to just more than tepid. Then stop beating and leave to cool completely. The meringue should look very white, be glossy and very stiff at this point.
In our Ask Peter series, executive chef Peter Gordon answers your curly culinary questions. If you're stumped over something food-related, send your question to firstname.lastname@example.org and keep checking in for answers. You can read more on Peter on his website, have a read of his Ask Peter articles or check out his recipes here.