White Vinegar Is The Ingredient You Need For The Fluffiest Meringue Topping
Lemon meringue pie may not be the simplest of recipes, but it dates back to the Victorian era, when elaborate dishes were in vogue. While you could opt to bake a simple five-ingredient lemon meringue pie using store-bought lemon curd (or a meringue-free yet equally lemony Atlantic Beach pie), Mashed recipe developer Tara Rylie prefers to stick with a more classic version. Her lemon meringue pie recipe will appeal to fans of food symmetry, as the number of yolks needed for the lemon filling is balanced out exactly by the number of whites used in the topping.
One ingredient you may not be expecting to see in a pie recipe is vinegar — no, not any of your fancy ones made from barrel-aged balsamic or fermented figs, but plain old distilled white vinegar, such as you might use to unclog a drain or de-scale a coffee maker. The reason for its inclusion, Rylie explains, is that it makes "the texture of your meringue ... mind-blowing" (in a good way, of course). She describes it as "extra fluffy [and] marshmallow-y," which is exactly what you want in a meringue.
Other acidic alternatives if you prefer not to use vinegar
Using an acidic ingredient in general to make meringue is actually standard practice, not anything super secret or unusual. The reason acid is necessary is that it helps to stabilize the egg whites once they're whipped. Otherwise, your meringue might collapse into a puddle on top of your pie. In addition to this structural improvement, an acidic addition helps egg whites whip more quickly, which was no doubt a great boon back in the pre-stand mixer days. Even though Tara Rylie assures us that "you won't even taste the vinegar" in her meringue, there are several other alternatives available if you're unenthused by the idea.
One acidic option called for in many meringue recipes is cream of tartar, should you happen to have any of the stuff on hand (and most likely you will if you're a frequent meringue baker). If you don't, though, lemon juice makes a great substitute for cream of tartar or white vinegar in baking. You won't have any reason to fear a flavor clash, either, as the pie is meant to taste of lemon. For either ingredient swap, all you need to do is exchange the vinegar for an equal amount of cream of tartar or lemon juice with no other alterations required.