Meringue is thought to go back to 1720, the invention of a Swiss pastry chef named Gasparini. You don’t need to be a pastry chef to whip up this airy confection. However, it helps to understand some of the chemistry behind the fluffy, melt-in-your-mouth texture of this seemingly simple confection.
Breaking It Down
The proteins in egg whites—especially the stronger proteins of fresh eggs—are the building blocks of meringue. First, however, these proteins must be partially broken down through a process called denaturation (dee-nay-chuh-RAY-shun). You’ll recall that proteins are wadded balls of amino acid chains. Denaturation breaks the chemical bonds that hold the chains in their tangles, allowing them to uncoil into long strands. Other chemical bonds remain, however, so the chains are still linked. Think of raveling the yarn of a knitted sweater sleeve without undoing the whole sleeve.
Denaturation may occur physically or chemically. For a meringue, egg white proteins are denatured physically by beating. Acidity plays a role in denaturing proteins chemically, in that fresh eggs are more acidic—another reason why they work better than older ones.
Building It Up
Uncoiled amino acid chains will join together, or coagulate. This too benefits a meringue. Think again of that raveled sweater sleeve. Making a meringue is like knitting a new sleeve in a more complicated pattern by working in another type of yarn. The extra “yarn” in this case is sugar. It’s “knitted” into the coagulating proteins during the beating process. Beating the whites also adds air, which becomes entrapped as tiny bubbles in a fine protein film, forming a foam.
Protein molecules can stretch only so far, however. Eventually they become weak and lose their water and “pop” like overfilled balloons. If this happens, the meringue may collapse in the bowl or later in the oven.
Sugar remedies this problem. When added after the egg whites start to foam during the beating process, sugar dissolves into the proteins. It bonds with them and lends them water, which increases their strength and elasticity. More bubbles form and the meringue swells—up to eight times the volume of the unbeaten whites.
Other factors promote meringue growth and stability. Acid slows coagulation, so more air can be added and drying is delayed. Many recipes call for vinegar, lemon juice, or cream of tartar to increase the foam’s acidity. As an alternative, some cooks use copper bowls to beat meringue. Copper molecules bind with one protein, conalbumin, for added support. This union also delays coagulation by raising the temperature needed for that reaction to occur. To avoid “doubling up” on the effect, acids and copper bowls should not be used together.
Taking the Heat
Even a meringue that’s perfect in the bowl—smooth, glossy, and slightly springy—is not yet a success. That requires the careful application of heat—in other words, baking.
A meringue pie topping is best baked at around 325ºF. At that moderate temperature, the air bubbles expand, the water evaporates, and the proteins coagulate at an even rate throughout the meringue. The result is a puffy, delicate, sugar-protein mesh. If the temperature is too high, the proteins set too quickly. The top browns before the water inside has time to evaporate. This water dissolves the sugar to form syrupy beads on the surface. Baking the meringue too long can have the same effect by driving out too much water.
The effects of underbaking may be seen when meringue is spread over a cool pie filling. Contact with the cool filling slows the rate of cooking. Again, the top is well done, but the proteins near the bottom have not set. This weakened structure collapses and leaks water, or “weeps.” The result is a meringue that slides on the filling when you cut the pie. In contrast, meringue that’s spread on a hot filling starts to cook at once to help prevent this problem. As a precaution, some cooks first sprinkle the filling with fine, dry cake crumbs to absorb any water that might form.
Topping a hot pie filling can avert another common complication—shrinkage of the meringue as the proteins coagulate. Likewise, spreading the meringue to the crust all around promotes even baking that discourages shrinkage. While making the meringue, you can also beat in a cooked paste of cornstarch and water after beating in the sugar. The starch reinforces the proteins, while limiting coagulation.
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