Wednesday, March 25, 2009

The chemistry of an epic meringue

Next in the series of food and its chemistry is: meringue!

This sweet, white, perfectly angelic confection has an almost mystical quality – how does it get so shiny, so crunchy on the outside, and yet remain a little chewy inside? Or, conversely, how does it stay perfectly soft in a meringue pie, yet still maintain its height and structure? Read on for the answer.

Meringue is made from some very simple ingredients – egg whites, sugar, and sometimes cream of tartar or cornstarch, as a binding agent, mixed together to make a foam.

A what?
A foam.
That’s all meringue is. Air, essentially.

A standard recipe is one egg white for every quarter cup of superfine, caster, or baker’s sugar. The egg whites are first beaten into soft peaks, the sugar is added tablespoon by tablespoon, while beating all the time to stiff peaks, which are very shiny and glossy, and remain stiff when lifting the beater.

That’s a general recipe – now on to the science!

The answer to a meringue’s feather-light baked structure and its voluminous height topping a lemon pie lies in the egg whites. These parts of the eggs are teeming with protein, and as such, they provide structure for the meringues. The amino acid bonds in the protein are denatured as the egg whites are beaten, which traps air into the fixture. Beating therefore serves the double purpose of breaking up amino acid bonds, and incorporating the all-important air into the meringue foam.

Next comes the sugar – this is the reason everything actually comes together and is stable. The proteins in egg whites cannot stretch and break down completely, which is what would happen after beating and baking them. The sugar, added bit by bit, bonds to the proteins and lends them more strength and elasticity.

The foam should be 5 or 6 times the volume of the unbeaten egg whites. Either spoon the foam into individual meringues on a baking sheet, bake a whole crust of meringue for a pavlova or a cake base, or use the foam on top of a pie. Meringues usually are baked long and low, that is, for an hour at least, and at a low to moderate temperature. With the heat, the air expands, the water naturally in the egg whites evaporates and no longer poses a problem to the structure, and the proteins coagulate to harden and form a crispy, shiny, light meringue. Perfect!

Some DON’TS:
DON’T allow any speck of yolk into the egg white mixture when separating them. This introduces fat to the mixture, which will kill the structure
DON’T use a plastic mixing bowl, or any bowl that is not meticulously clean. Again, fats tend to stick and therefore would contaminate the egg whites.
DON’T stop once the sugar has been added and the eggs are being vigorously beaten. The mixture will break otherwise
DON’T start making meringues on a rainy or humid day, or store the finished product in the fridge, or allow any water to come into contact with the meringue. Water softens and destroys meringues.

NB: no actual recipe is provided. This is a general look at what substances go into meringues, and how each reacts chemically. When actually baking, use a real recipe (like one with measurements and oven temperatures.

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