Fade to Green

We're growing Royal Burgundy beans in the garden and harvested our first bunch yesterday. The purple color of the beans makes them a lot easier to find on the vines especially when voracious DC mosquitos are having a Vegas style buffet at my expense. Unfortunately, within seconds of dropping the beans into hot water the purple color fades to green.


Off to Google to find out why.

The answer from the Christian Science Monitor...

A natural group of chemicals, called anthocyanins, are what put the purple in purple green beans, as well as in grapes, plums and, less familiar, purple broccoli.

Two things happen during cooking to make Royal Burgundy beans turn from purple to green. A direct effect of the heat is to cause decomposition of anthocyanin. Less anthocyanin means less purple. The indirect effect of heat is to burst apart cells, diluting the acidity of the cell sap.

The green color, which was present but masked by the anthocyanin, becomes prominent once the anthocyanin concentration drops, and what anthocyanin is still left becomes bathed in liquid insufficiently acidic to keep it purple. A similar thing happens when you cook red cabbage. It turns colorless after awhile. You can also expect purple broccoli, purple asparagus, purple tomatillos, even purple peppers to lose their purple color after cooking.