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You can do so many things with even a small amount of egg white. As they are the best ingredient for capturing air, you can expand even a single egg white into a bowlful of foam. There’s nothing much to egg whites – they are just water plus some proteins. The part that makes them so useful is the properties of the protein. After it has uncoiled a little, it forms a network that traps air bubbles really well.

Keeping egg whites

Very few people outside the catering and restaurant industry seem to know how stable egg whites are. If you separate eggs and use the yolks, you can put the whites into a clean container, cover with cling film and store in the fridge for weeks, even months. You can also freeze them without any problem. Just be sure to defrost them carefully – you can easily cook them by accident if you microwave frozen egg whites!

Working with egg whites

There are a lot of legends surrounding egg whites. You do need to keep any fat away from them if you want to whip them up. That means that glass and metal bowls are best – plastic ones aren’t a good idea. Things that help: a little bit of acid works well – a couple of drops of lemon juice, or a pinch of cream of tartar. If you don’t do these things, the egg whites will still increase in volume, but won’t reach quite the same heights of stiff peaks.

Many recipes with whisked egg whites require stiff peaks. If you whisk too far, however, the egg whites will break up into little lumps as you fold them into something else. Both the acid and copper, if you use a copper bowl, will create a stable foam that takes longer to reach this pebbly stage.

When working egg whites into a thick batter, like a cake batter, you can use a portion of the egg whites to loosen the batter first. Just take a large spoonful of the egg whites and stir into the batter without worrying about the air. The liquid in the egg whites will loosen the batter enough to make it easier to fold in the rest and preserve the

Meringues

Adding sugar to egg whites stabilises the foam. Once sugar has been added to a meringue mixture, you can beat it for a long time, and it will just get stiffer. If you’re piping the meringue, or adding other ingredients (such as ground almonds for macarons de Paris), you want the mixture to be as stiff as possible so it will hold up when the other ingredients are mixed in. Meringues can be spooned or piped onto parchment paper for baking.

Meringues are intensely sweet, so it is nice to add a bitter or toasted flavour to contrast with it. Toasted nuts and caramel create complicated, toasted flavours that can make the perception of sweetness less acute, by making it less simple.
Coffee and brown sugar meringues temper the sweetness of white sugar. Adding a thick bland filling based on true buttercream, or perhaps on barely sweetened whipped cream, will also contrast with the sweet meringue.
I like an Alice Medrich recipe that combines dark chocolate, ground in a food processor, with stiff meringue. These are piped in small peaks and baked to give a crisp meringue cookie, with bursts of chocolate flavour.

Macarons

Ms Humble has the best guide to macaron making – in a series of completely comprehensive posts, she goes through every possible hint and tip you could know about. (She also has awesome science cookies posts).
In my own experience, it can be hard to get the ideal shape and texture, but almost every macaron is worth eating, even those that don’t look too beautiful.

You need to make a really thick meringue mixture, so it will hold after folding in the almonds, and while you’re piping. However, too much air will mean a more grainy surface and you won’t get such a smooth skin forming on the surface. You need to dry them a little before they are baked to get that smooth skin. Ms Humble has lots of ideas about the much harder task of getting something that’s crisp on the ouside, soft on the inside, and neither hollow nor sticking to the sheet.

(Below are a pistachio macaron from Alain Ducasse at the Dorchester on the left, and my attempt on the right).

Coconut macaroons are much easier – you make a stiff mixture with them, cooking the mixture a little in the saucepan before spooning onto a baking sheet. Here, the sticking power of the protein is much more important than its foaming properties. David Lebovitz has a nice recipe for coconut macaroons.