How To Save Egg Yolks When Your Recipe Only Calls For Whites
If you're a fan of baking, then you've probably encountered recipes that call simply for egg whites and not yolks. Dishes like meringue cookies, sponge cake, or even some soufflés will call for you to separate the yolks from the whites, and in most cases, you simply throw out the yolks.
While there are always creative ways to prevent food waste by using discarded egg yolks right away, like making spaghetti carbonara, flourless chocolate cake, or an egg custard, you might find yourself in a position where you don't have a plan for the yolks right away and need to save them for later.
Nonetheless, popping leftover food items in the freezer is generally a safe bet for preservation, but when freezing egg yolks, you'll run into a problem. Egg yolks themselves contain water crystals, and when frozen will cause the proteins in the yolk to form a cluster that won't be easily broken once they thaw out again. This means if you cook or bake with those thawed yolks, you're going to run into a textural issue. However, thanks to science, there is a very simple, sweet solution. By whisking simple syrup with the egg yolks before freezing you prevent them from clumping as they freeze. This way when they thaw out you'll have a better texture. No sugar in the house? No problem, the same can be done with a pinch of salt.
A simple solution
While commercial restaurants and bakeries will have preservatives called cryoprotectants on hand that keep the yolks from tightening up too much when frozen, a home baker is less likely to have such an ingredient in the pantry. So what can you do to preserve the yolks properly?
It turns out that most cryoprotectants contain sugar, which disrupts the proteins when they freeze and keeps them from clumping, so sugar can give the assist when it's time to freeze the yolks. Where you'll run into trouble is using granulated sugar. Depending on the size of the granules, sugar won't always break down the way you want it to when it's whisked into cold yolks before freezing, so the best solution is to mix a bit of simple syrup with the egg yolks before you freeze them.
To treat your egg yolks before freezing, make a simple syrup of two parts sugar to one part warm water. Allow the sugar to dissolve and the syrup to cool before you mix it with the yolks. Measure ¾ teaspoon of cooled simple syrup per four egg yolks. Whisk the mixture together and save in a freezer-safe container for up to two weeks. These slightly sweetened egg yolks are perfect for baking recipes.
How to use thawed yolks
One of the best ways to freeze egg yolks is in a silicone ice cube tray. Once you whisk the egg yolks with your simple syrup or pinch of salt, divide them up so that about one yolk fits in each divot of the tray. This way you'll know how many cubes you need to defrost for your recipe. If you don't need to know a specific number of yolks for future recipes, then you can simply store your mixture in a freezer-safe ziplock bag.
Egg yolks that are preserved with a sugar-based simple syrup are perfect for baking recipes that call for a lot of egg yolks like a creme brulee or egg custard tarts. You can also use sweetened yolks for French toast. If you want to save egg yolks for savory dressings, pastas, or your favorite aioli recipe, then use the salt trick before freezing them and you should have a similar result.
Remember that the safest way to prevent foodborne illness is to thaw your frozen items in the refrigerator, as per USDA. So, when you plan to use these frozen yolks, allow them ample time to defrost in the refrigerator. Employ these simple techniques, and you'll never have to toss an egg yolk again.