It happens even to the best of them, moist and sweet homemade blueberry muffins, made with care and love, but that end up with unsightly green blobs of what should have been pretty purplish blueberries. The taste is the same, but the color of the blueberries wasn’t expected. That, my friends, is anthocyanin‘s fault. But actually, to be more precise, the pH of the muffin batter also has a role in this story.
What is anthocyanin?
I guess I should actually say “anthocyanins,” plural because actually anthocyanins are a family of similar compounds. They are the antioxidants in plants, like leaves and berries, and they are responsible for much of the color you see on the tables at the farmer’s markets, from red cabbage and purple corn to many different types of berries, cherries, and grapes. The anthocyanins are not to be confused with the carotenoids (like beta-carotene): carrots get their orange color (and even purple color) from beta-carotene, while blueberries get their violet-blue tones from cyanidin 3-glucoside (an anthocyanin).
Why do anthocyanins change color?
Anthocyanins are actually really good pH indicators: they change color depending on if they are in an acidic, neutral, or basic (alkaline) environment. The color changes observed vary from one anthocyanin to another, but for cyanidin 3-glucoside, the anthocyanin found in blueberries, the color varies from red to violet to blue or even green (from low, acidic pH to higher, alkaline pH). A change in pH entails a small change in the structure of anthocyanins, like cyanidin 3-glucoside, thereby affecting how anthocyanins absorb/reflect light rays: they change colors.
What do anthocyanins have to do with the color of the blueberries in my muffins?
The answer is easy: does your recipe have a lot of baking soda, with the hopes of giving those muffins lots of oomph and volume? If there aren’t enough acidic ingredients in your recipe to balance out that alkaline baking soda, then your muffin batter will be basic (alkaline)… your blueberry muffins will probably have splotches of green berries, instead of violet.
If your favourite blueberry muffin recipe yields the best muffins you’ve ever tasted, but the blueberries end up an unfortunate green, know that it’s not the end of the world, but if that green color bothers you, make a note. In the next batch, consider adding in a little extra vinegar (or buttermilk, or whatever acid that is called for in the recipe) to balance out the extra baking soda, or you could even use a touch less baking soda in the next recipe.
Here’s a recipe for yummy honey blueberry muffins on Kitchen Heals Soul.