In brief
Aquafaba is the liquid drained from chickpeas, which can be whipped into a foam.
Useful to know
Aquafaba is the liquid drained from chickpeas, which can be whipped into a foam. King Arthur considers uses as an egg-white substitute while explaining that not every substitution succeeds. [1]
For a first attempt, choose a recipe developed for aquafaba. It does not automatically perform every role of a whole egg: egg white, yolk, fat and structure are different functions. If saving the liquid, follow explicit storage directions. Creating a foam alone does not prove that the finished bake will have the desired structure.
Sources
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