A few weeks ago Evan Kleiman of KCRW's Good Food tweeted me a question from one of her listeners: why did the cooking water for a batch of garden green beans turn pink? Not knowing for sure, I guessed that the color came from early stages of the browning discoloration that develops when many fruits and vegetables are cut or damaged. Mushrooms are especially prone to this, and I've noticed that they turn pink before getting more frankly brown.
Shortly after replying to Evan I happened to pull out a half-dozen fava bean plants from my garden, and I harvested pounds of green pods, old and young. I enjoyed the tender ones whole, tossed in a hot pan with a little oil and salt. They're deliciously different from ordinary green beans, with a flavor that's both meaty and flowery, even perfumed. The older pods I pulled open to collect the beans in their tough seedcoats. I blanched a batch of these beans in boiling water to soften the skins and speed the tedious peeling. And I noticed that the blanching water became pink, especially under incandescent light (below).
This reminded me of how quinces and pears can turn pink and even red when they're slowly poached. They do so because they contain compounds called proanthocyanidins, molecules that don't participate in the usual fruit browning, but that fragment during cooking into anthocyanins, the pigments that color most red fruits and vegetables.
So I checked, and it turns out that the skins of most legume seeds, favas included, are rich in the same proanthocyanidins.
New theory! Colorless proanthocyanidins in bean seedcoats release fragments into the cooking water, and these are what turn the water pink.
I thought I could test the theory by cooking some skins by themselves and adding either citric acid or alkaline baking soda to the cooking water. Anthocyanin pigments are sensitive to pH. Acid usually shades them toward the red, alkali toward the blue. So if the fava seed coats are indeed releasing anthocyanins into the cooking water, I should be able to change the water's color.
Well, the color test didn't turn out the way I expected. The acid cooking water was the same pale pink as the neutral water, and it was the alkaline water that turned a deep, winey red (right). I still haven't figured that out.
But I noticed something else that was easy to figure out, and much more useful than any color change. Whenever I cooked fava beans in alkaline water, more than half of them popped their skins in the pot, no hand-peeling needed! And the rest were easy to peel with a gentle squeeze at one end.
Here's a batch of alkaline-blanched favas fresh out of the pot, before any hand-peeling.
The skin-busting effect of alkaline cooking water makes good sense. Acidity maintains the structure of plant cell walls, and alkalinity breaks it down. That's why beans take forever to soften if you try to cook them in a tomato sauce. So soda in the blanching water weakens the fava seed coats enough that many of them rupture on their own in a couple of minutes at the boil, and the remainder easily break between finger and thumb.
Using soda seems such an obvious idea in retrospect that I'm surprised it's not already standard practice. Many recipes for dried favas do call for baking soda to soften their skins and speed the cooking. There must be other cooks out there who've been blanching fresh favas with soda. I'm now one of them.
So: to ease fava peeling, add about a tablespoon of baking soda to a quart of vigorously boiling water, and throw in the beans. Fish them out as they pop their skins so they don't pick up the soda soapiness, and drop them in a bowl of cold water to rinse. After two or three minutes, scoop the remainder into another bowl of water to cool them down. Peel them by gently squeezing on the thick end of the bean, if necessary nicking the thin end with your fingernails.
And check out the color of the cooking water before it disappears down the drain. It's a sign of the chemical defenses concentrated in the seed coats, and their likely nutritional value for us. That's the next challenge: making fava skins delicious enough to keep and eat with pleasure.