Meringue

Gisslen tops cream pies with a common or Swiss meringue of one pound of sugar to each pound of egg whites, whipped stiff, spread generously and attached to the crust all the way around so it cannot slide on the finished pie. Sunset explains the foam: cream of tartar, added before the whites reach a coarse foam, strengthens the bubbles, and sugar beaten in gradually breaks them into smaller, firmer ones. Sugar added too soon makes the whites too stretchy; added too fast, it does not dissolve. Overbeaten whites lose their gloss, and their bubbles pop and drain in the oven.

Two defects are named for where the liquid appears. Weeping is a layer of liquid between meringue and filling. The Exploratorium attributes it to water leaking from the whites, which are 87 percent water, when the underside of the meringue never cooks. Beading is a scattering of syrupy droplets on the surface. Ricardo blames beading on overbaking, in which surface proteins coagulate too far and expel water, and blames the layer underneath on underbaking. Iowa State’s food preparation manual lists undissolved sugar and overbeating as further causes of beading.

The temperature of the filling is the main point of dispute. The Exploratorium, Sunset and Ricardo all spread the meringue on hot filling. The Exploratorium reasons that heat from the filling cooks the underside while the top browns. Sunset adds that steam from a hot filling passes through the meringue instead of condensing at the join, and that meringue swirled onto a cool filling weeps and slides off when cut. Iowa State’s manual agrees that cold filling causes weeping, but lists baking on hot filling as a cause of beading, while still recommending it for food safety. Sunset itself attributes beads to steam from the hot filling collecting near the surface and recommends a little cornstarch in the meringue to hold it.

Oven temperatures vary with the source. Gisslen bakes at 400°F and warns that higher heat shrinks and toughens the surface. Ricardo bakes meringues of four or more whites at 325°F for 20 to 25 minutes. The USDA’s 2001 egg-safety guidance states that meringue-topped pies should be safe if baked at 350°F for about 15 minutes, and LSU AgCenter repeats that standard, which rests on the 160°F temperature that kills salmonella in egg dishes. Sunset notes that a meringue baked longer at a lower temperature holds up better than one baked briefly at a high one.

A meringue pie does not keep. The Exploratorium recommends eating lemon meringue pie the day it is made, because moisture accumulates as it sits. University of Wisconsin Extension directs that lemon meringue and chiffon pies be refrigerated until served, and Iowa State Extension counts meringue pies among the egg-rich pies the USDA says should not stand at room temperature more than two hours.