I have fresh purple and yellow beans that go green when they are cooked — would you know of any way I could prepare them to keep their colour? Jacqui
It’s a good question, and one that’s often asked. I remember buying a bag of purple capsicums years ago and being very excited at the prospect of serving grilled ones on top of steamed white fish with vivid green pesto. I thought the colours would look amazing. Unfortunately, the minute they were grilled they lost all of their purple colour. I made a salsa with a few more and managed to keep some of the colour (I also used red onions and sliced cherry tomatoes) by dicing the raw capsicums and mixing with lime juice and zest. I realised that there must be a chemical that makes them purple in the first place that reacts well with acid. It turns out that chemical is called anthocyanin and it occurs in plums, purple broccoli, red grapes and I’m guessing red onions.
Of course, acid is what we do our best to keep away from green vegetables for any length of time as it fades the green and can produce a grey coloured bean. Adding something alkaline to a pot of boiling water will keep your greens super-green — which is why a good pinch of baking soda added to the pot will keep your broccoli looking amazing. But the thought of adding vinegar to a pot of boiling greens just seems plain madness don’t you think? Instead, try tossing the purple vegetables in a mixture of 2 parts vinegar (don’t use malt — it’s already too brown) with 1 part cold water and leaving for a minute, before steaming or boiling them. I’m hazarding a guess that this might work. But it may not. If I had a bag of purple beans with me now I promise I’d try. My excuse is that I’m actually prepping for an event for the New Zealand Film Commission in L.A. tonight — it’s Waitangi Day here — and unfortunately purple beans aren’t on the menu. Plenty of New Zealand venison, elk, lamb and beef, along with clams, salmon, greenshell mussels, kawakawa, horopito, honey and manuka-smoked salt are though. More about tonight’s food in the next few weeks.
When I make a salsa that contains red onions, I usually always treat them in the following manner. Peel and cut in half vertically. Then slice them as thin as you can from base to top, rather than the half moon shape. Pull the layers apart and if they’re quite “teary eyed” type onions, rub with a few teaspoons of coarse salt between your hands and leave for 10 minutes. Friends in Istanbul do this, and they refer to it as bruising the onion. Rinse with cold water then pat dry with kitchen cloth. Mix with red wine vinegar, cider or rice wine vinegar, or lemon or lime juice, and your onions will be vivid pinky red. If the onions aren’t causing tears, then skip the salting part (but it does feel good, rather like a severe hand exfoliation).
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As for keeping yellow beans yellow, I find they stay yellow once cooked. If yours are changing then perhaps blanch them in heavily salted water and cook a little underdone. Drain and plunge into icy cold water. Mind you, if you’re wanting to eat hot yellow beans then this won’t help, of course, but it’ll be good for salads and the like.
In our Ask Peter series, executive chef Peter Gordon answers your curly culinary questions. If you're stumped over something food-related, send your question to email@example.com and keep checking in for answers. You can read more on Peter on his website, have a read of his Ask Peter articles or check out his recipes on our site.