Why do chilli peppers change colour when they go ripe?

02 August 2009

Question

Why do chilli peppers change colour when they go ripe?

Answer

We're growing some chilli peppers on our window sill. Actually, my chilli plant got some fungal disease and died though or nearly died. I've managed to resuscitate it but I had to spray something on it. It's says, "Do not use on things you intend to eat," so while I saved the plant, it's now useless because I can't actually eat it. Anyway, we're growing some chilli peppers on our window sill. For ages they've been green but suddenly they're going beautiful red and yellow colours. I understand the process why most plants are green but why do the peppers turn red and yellow? What's the point in that?Helen - Actually, I'm growing my own chilli peppers too, failing too as well. So if you've got any tips on how to do it better, I'd love to hear from you. But, well if you think about it, it's kind of a two-sided question, really. First of all, why does any kind of fruit or anything that might be eaten change into a bright red colour and usually that's if it's ripe and ready to go, it's advertising itself to be eaten by a disperser. An animal of some sort is going to come along, have a nibble, eat it, take the seeds in its stomach and release them somewhere else in the faeces to help disperse this plant. That's okay if you're a nice tasty thing like a tomato. They start out green and they don't want to be eaten before they're nice and ready, before the seeds have actually developed enough. So they will later on turn to be red and there you go. That's why they turn red, but why do chillies turn red? Do they actually want to be eaten given that they're so spicy? Do animals actually like to eat chillies? Well, there's lots of theories about why chillies evolve to have such spiciness and capsaicin is the chemical that actually makes your tongue burn when you have a mouthful of chilli, and I love it as well. And a guy called Josh Tewksbury, a scientist in the University of Washington who spent a lot of his time looking into this question of how spicy chillies evolved, why they evolved. What's the purpose of them? He's been out in the Bolivian and Peruvian jungles where we think - well, sorry, the rainforest, the dry mountainous areas, actually not rainforest, where we think these chillies first evolved and he's found some really interesting things out. So, we think that it could actually be that mammals are no good at eating chillies because they actually crunch them up. They're seed predators. That's not much use to the chilli plants; their seeds get destroyed that way. But maybe birds are the ones that the chillies are trying to attract because birds usually just swallow down the seeds whole and they don't actually get affected by the chilli and they've watched to see. There are natural variations in the amount of capsaicin you get in plants within one population of chillies. They went out and looked and they saw that mammals don't like to eat the ones where there's lots of capsaicin in the plants. But birds don't mind, they would just go for any of them.Chris - I think, they actually lack the receptor that the capsaicin locks on to on the nerve fibres.Helen - Right, there you go.Chris - So they can't detect it.Helen - That as well.Chris - Because one suggestion we did have for people who keep chickens and are fed up with rats eating the chicken food is that you put loads of curry powder in with the chicken food and the chickens don't notice the curry powder because they're insensitive to the effect of capsaicin.Helen - There you go.Chris - But the rats do and the other benefit of that is that you get a sort of premarinated chicken, so when you come to eat it, it's already nice and currified.Helen - Super! Super! It's also could be that it could deters fungal attack and that in fact having more capsaicin in the chilli plants, in their seeds helps to avoid fungus coming along and destroying the seeds. Maybe it's attracting birds that's why chillies are red but we've been doing it for an awfully long time, at least 6000 B.C. we think that chillies were being cultivated.Chris - With good reason, they're fantastically tasty.And we had a comment from Judith in Northhampton who said that capsaicin powder can be used to stop things eating your chicken food. She uses the same trick to stop the squirrels in nicking her bird feed.

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