Re: Why does pomegranate juice dry different colors?

Much of the color in pomegranates comes from a class of molecules called anthocyanins. These types of molecules are present in many plant tissues, especially those that are red, blue, or purple – blueberries and red cabbage are examples. An important property of anthocyanins is that they shift color depending on pH (acidity); they appear red in more acidic conditions and blue in more basic conditions.

Here’s my guess as to what happened: The juice that dried on the counter just dried without its pH changing, so it stayed red. Much modern paper is “acid-free paper” and it has ingredients that neutralize acid. So, probably, the juice on the paper had its pH increased (which is the same thing as making it more basic) because of its interaction with the paper, and the anthocyanins partly changed to blue, leaving you with a purple color.

If you still have the paper, you might be able to confirm this hypothesis. Put a tiny drop of white vinegar (which is acidic) on one part of the dried spot; put a tiny drop of regular water on another part. The water is your “control” in this experiment. If it works the way I’m guessing, the part wetted with vinegar will turn back to red.

Good luck!

Rafael

**The author is answering this question on his own behalf, and this answer should not be interpreted as a statement originating from his employer.**