Why do apples turn pink?
JS (my boyfriend) and I headed way out of the city last week, passing several barn sales and too many water towers to count on our way to the ultimate fall experience: apple picking. The grounds were lovely and the apples (and requisite donuts) beyond delicious, but I stumbled upon a puzzle deep in the east orchard that’s been bugging me.
Wandering into the rows of Ozark Gold apples, we each picked one and bit into it. JS excitedly told me that these were the best yet, while I wanted to head back to the Empire section. We compared our apples and then traded. His (larger and pink on one side) was just as good as he had said, while mine (smaller and gold all the way around) made both of us wince. This finding held up as we sampled more–gathering evidence is a very important part of the scientific process!–and it made me wonder what was going on.
First, what turns some of the apples pink? Apparently it’s a compound called anthocyanin, the same molecule responsible for the bright red of fall leaves. Sunlight and cold temperatures both increase anthocyanin production, which is why we saw the pink-blushed sides of the apples lined up toward the sun. The temperature dependence means that the same apple variety will look different grown in Wisconsin and Mexico, for example, and Chicago’s chilly fall nights probably helped our apples become so beautiful.
So anthocyanins explain the skin color variation, but why were the pink apples so much yummier? The molecule itself is essentially flavorless, but it lets us know what’s going on inside the apple. Immature fruit produces hormones called gibberellins that prevent anthocyanin formation, keeping the fruit green. When it becomes fully ripe and flavorful, gibberellin levels drop, anthocyanin production gets going (helped by the sun and the cold), and the skin’s pink tinge lets us know that it’s ready.
The color also reflects the kind of apple, of course, and an apple grown in a warmer climate could be just as good without the color change. But for us and our Ozark Golds, the sweet pink blush gave away which apples would be our favorite.
And what have we been doing with our pink-cheeked bounty? Besides eating approximately three a day, it wouldn’t be apple season without apple pie, and applesauce is in the works. This might be my favorite time of year.
Thanks to extension.org, Science is Fun from University of Madison, and Max Saure’s “External control of anthocyanin formation in apple”.