The Reason Your Onions Are Turning Blue

Onions come in all different colors. There are red onions, perfect eaten raw on burgers or in salads, and white and yellow onions, which are excellent all-purpose choices. There are even green onions, if you want to stretch the definition a bit (just so long as you don't call them chives). But what happens when you throw a handful of red onion into a skillet for your frittata and see those onions, once a healthy shade of purplish-red, turn colloidal-silver blue? Do you scream? Faint? Call an exorcist? Don't worry so much: It's the result of a natural chemical process, and while it can be jarring to see it happen in person, blue onions are perfectly safe to eat.

Red onions contain natural pigments called anthocyanins, which give them that lovely coloring. But anthocyanins are quite sensitive to pH levels — that is, how acidic or basic something is. When they're introduced to something more basic, or alkaline, those pigments will shift in color, resulting in that startling shade of blue. Egg whites and baking soda are two alkaline substances that might trigger this reaction.

So what should you do if you see your red onions going the way of Violet Beauregard from "Charlie and the Chocolate Factory?" Well, if you want to offset or reverse the chemical reaction, you can always introduce an acid to your dish: lemon juice, vinegar, or cream of tartar (which can also provide a flavor boost to tomatoes) are just a few possibilities. But that might result in a flavor combination you may or may not be looking for. There's nothing wrong with a bright, acidic note, but there's a time and a place for everything, you know? You could also just avoid combining red onions with anything, especially alkaline, in the first place.

But honestly, it's really not a big deal. Sure, it might cause some presentational issues, but that's about the only harm blue onions might do to your dish. Not only are they safe to eat, but their flavor is totally unaffected by the process of changing colors. Hey, they always say you should have a colorful plate of vegetables, right?