meringue [muh-rang] noun
A mixture of beaten egg whites and sugar.
You will find soft meringue covering pies, such as in lemon meringue pie; adrift on a pool of custard sauce such as in the classic dessert, Ile Flottante; as a basis for Italian or Swiss meringue buttercream; or as a main component of angel food cake. Hard meringue takes the form of cookies; dessert shells such as Pavlova to hold ice cream and/or fruit; or discs, sometimes with ground nuts added, in which case they technically become dacquoise and Japonaise.
There are three main types: French, Swiss, and Italian. The French meringue is uncooked, the Swiss is heated in the top of a double boiler, and Italian is made with simple syrup that has been brought to a high temperature (such as 248° F for Italian Meringue Buttercream).
An acid such as cream of tartar, or sometimes a little lemon juice, will often be added once the eggs have been beaten to the frothy stage. The acid helps stabilize the proteins in the egg whites and creates more stable foam. The classic French unlined copper bowl accomplishes the same task: the proteins react with the copper, which provides some stabilization.
All meringues depend on egg whites beaten to an increased volume, and this can only be accomplished if you have scrupulously clean tools and not even a speck of egg yolk in your whites, so take care when separating your eggs. Our test kitchen has not had good results from purchased egg whites. Even when the label says that the product is 100% egg whites, they do not whip up well.
When making a hard meringue (cookies, Pavolva, discs) the recipe will call for low oven heat, typically between 200° F and 275° F, and a long baking time. The aim is to dry the meringue, which results in the desirable crisp texture. Some older recipes recommend drying out the meringues overnight in a turned off oven, but this was due to the presence of a pilot light, something most ovens lack at this point.
Once baked and cooled, hard meringues must be stored completely dry and airtight. It really is best to prepare them as close to the time of dessert presentation because truthfully, they do not store well. Some commercial kitchens use silica gel packets inside airtight containers to keep meringues dry. These are the non-edible packets you sometimes find in food containers or even packed with footwear and other non-food products.