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Ever Wondered About... Berries?

Updated Wednesday, 17th February 2016

Paul Merrett and David Shuker discuss the science and significance of berries.

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Strawberries and blueberries Creative commons image Icon Steph L under Creative Commons BY-NC-ND 4.0 license Creative-Commons The Open University


Paul Merrett: Hi, I'm Paul Merrett, and I'm the chef and the presenter of the BBC Open University TV Series Ever Wondered About Food? And if you haven't ever wondered about food, I reckon you're in the minority. We've spent weeks dissecting things, chopping things up, weighing things and measuring things, just so that we can bring all that information to your TV. And, throughout the series, the person that's really made all the science bits happen for me is David Shuker of the Open University - and I've got him right here.

David, when I was a young cook, doing my apprenticeship, my Head Chef said something very interesting to me; he said, "You'll always learn things better if you get them wrong the first time." And I sort of know what he means now because, until you hit a problem, you don't really think about the solution. So, if things are always going right, you don't ever wonder what could go wrong. But if it's gone wrong, then you have to think about the processes you've gone through and put one of those right. Do you find that in science that's the case, or is it a much more cut and dry, black and white thing?

David Shuker: Paul, it's very much the situation. Science is interesting actually because I run a research group and some of my research students sometimes come to me and they say, "This hasn't worked." And, interestingly, one of the pejorative things we sometimes say about the lab is that we're following a recipe, in the sense that we're just doing it; because a recipe is something that you go through the steps and it works and that's fine, you don't really have to understand all the little bits of nitty-gritty.

Well, what happens is, of course, that sometimes "the recipe" doesn't work. Something… you know, you don't get the outcome that you want. And then that's the time - just like you've found, like your Head Chef said to you - it's when things go wrong that you really begin to have to face up to "do you understand what's going on?" because, in order to fix an experiment or a dish that's gone wrong, then you need to have some idea what the key steps are so that, in fact, depending on what's gone wrong, you can say, "Well, what might explain that?"

I mean - a good example I often find myself when I'm trying to make something in the kitchen is that, for example, you want to make a dressing and you mix it all together according to the recipe and it doesn't form a nice, smooth dressing, it separates. And so you ask yourself, "Well, why is it separating?" And, interestingly, the science of that is fascinating because it depends, for example, whether you've got an oil in water emulsion or a water in oil emulsion; if you guess it the wrong way round you keep on piling in more oil and it just separates even more.
So that's just one example but there are many other things, and some of them a bit less obvious to sort out. But I'd be interested to know, for example, I mean, in some of the cooking that you do - some of the dishes that you prepare - you know, times when it sometimes can go wrong - I'm sure it doesn't go wrong very often - but, when it does go wrong, isn't understanding a bit about what's actually going on in that dish important?

Paul Merrett: Yes. It's hugely important. But, I've got to admit, for years I don't think I really considered it on a scientific level. I would follow recipes carefully and I would think hard about what I'd done and what I'd seen other chefs do, but I don't think I actually sort of tried to break it down quite as much as I do now. Because one of the things I've taken away from doing the programme is looking at food, looking at a recipe, at its ingredients first and trying to understand what each one of them is doing in there. And, in fact, something I have noticed about recipes is that quite often there's things that don't need to be in there. You know, the pinch of flour that goes into pastry making - well I'm still pondering that one, I can't think of a reason it's in there.

So, I think now I've started to juggle and deal with recipes in a different way. We made muffins on the Berry programme, and one of the things I'd like to know is, why does a recipe call for self-raising flour in one instance and plain flour with raising agents in another instance - what's the difference? Surely, self-raising flour is just a pre-made mix of the other, isn't it?

David Shuker: Well, of course, it depends really what raising is about. What raising is all about is finding some way of getting a gas - the news of that gas is CO2, carbon dioxide - into the mix so that, as it's cooking, you get that lightness of texture, which is the gas either forming bubbles in the mixture or just being in the mixture and making the whole thing rise.

Paul Merrett: I should say, we were making muffins - so quite a cakey mix.

David Shuker: Absolutely yes, yes.

Paul Merrett: That's what we're talking about.

David Shuker: And, of course, what you put in there, in that recipe, you're using baking powder?

Paul Merrett: Yes.

David Shuker: Now, you could use bicarbonate of soda. Now, bicarbonate of soda is something that, if you heat it, it'll break down and give off carbon dioxide. But, the trouble is, it's slightly alkaline.

Paul Merrett: So that would mean, rather than you incorporating the air, it's incorporating a gas to lift the thing for you?

David Shuker: Exactly. And, in fact, well, it turns out that baking powder is really a solid form of carbon dioxide. It's a convenient form; rather than pumping CO2 from a cylinder in there, what you do is, you add this powder and as you heat it during the cooking it gives off carbon dioxide right inside the mixture.

Paul Merrett: So where do we go then to get baking powder? I mean, you know …

David Shuker: What is baking powder?

Paul Merrett: Yes, where is it from? What actually is it?

David Shuker: Well, okay. Bicarbonate of soda is something you can buy in shops and is used in cooking. You can't use it in this recipe because it makes the mixture too alkaline and that would affect the colour of the berries.

Paul Merrett: Yes, and I think, to the cook's mouth, it gives a fizz on the tongue.

David Shuker: …a fizz on the tongue, exactly.

Paul Merrett: I can detect things which have used bicarbonate.

David Shuker: That's right, because what happens is that, if you mix bicarb with a bit of acidity, then that rapidly decomposes the bicarb and gives you that fizz of CO2, just like the CO2 you get in lemonade for example. What you do in order to make baking powder is, you mix the bicarbonate of soda with a solid acid, and that's cream of tartar, which is a bit of… citric acid is the more technical name for it.

And what happens is that, in the dry state, they're very happy to sit there and it doesn't decompose. But if you put baking powder into a mixture which contains a bit of water, then it begins to give off the CO2. But that's a chemical reaction, and most chemical reactions go much faster when you heat them up so, as you heat the muffin, that decomposition begins to accelerate and that means that, as the muffin is cooking, the CO2 builds up in there and it pushes the whole mixture up.

Paul Merrett: And why doesn't it collapse back down?

David Shuker: Well, because…

Paul Merrett: I'm assuming it must be a structure that is cooked into place once the thing's lifted.

David Shuker: Yes. Well, of course, as with all recipes, there are lots of different things going on while you're cooking it, and what's happening is that the flour and all of the other constituents in there, they're undergoing changes which means as they expand, when you take it out of the oven, it cools down and it kind of solidifies, almost like forming a scaffold. But by then the carbon dioxide has done its job. And so it doesn't need to be supported by the gas, it's been puffed up and then it sets, as it were, and then it's okay, and as it cools down it keeps the shape.

Paul Merrett: Right, well that's - yes, so there you are, a simple recipe but someone, somewhere along the line - and that's what always amazes me about recipes, someone, somewhere along the line must have thought to put that in there in the first place.

David Shuker: That's right. And what they've done is, because all recipes, all cookbooks, are full of the accumulated wisdom of the years, so people have tried things. And, of course, people have tried things that didn't work and, of course, what's interesting is, you don't see the stuff that doesn't work. So you say "Well, why don't we, for example, add yeast to a muffin mix?" Well, first of all it gives a different… it's another way of raising but it gives a different kind of flavour.

Paul Merrett: …or egg whites or something like that.

David Shuker: …or egg whites - or you whip in egg whites. So there's all the ways you could do it. It just so happens that, for the flavour that you want and the consistency you want, you want that chemical rise, which is what baking powder is. But, yes, I'm sure people have tried it and what they've found in the past is that it doesn't give you the right thing so they've just put it to one side; it doesn't work.

Paul Merrett: Ditch it and move on, yes.

David Shuker: Yes. But then, sometimes, you know - I mean here's a good example: what happens if you forget to put the baking powder in there? I mean, you mentioned all these recipes where you put a pinch of this and a pinch of that and what's happening, of course, is that sometimes you can imagine an apprentice chef, or even an inexperienced cook in the kitchen, you think "Oh, it didn't work," you think "Oh, wait a minute, I forgot to put in something."

Paul Merrett: I've been there.

David Shuker: And, of course, that's why - again, it's "Why do you put things in?" and "Does it matter if you don't add things?" Because often you hear people in the kitchen say "Well, you know, perhaps it doesn't matter if I don't leave something this long to do this" or, you know, "if I miss out that ingredient." Well, of course, it probably does matter an awful lot.

Paul Merrett: But trial and error is a great thing, and I think that quite often you can play around with recipes …

David Shuker: …and get something new, there's always something new to discover.

Paul Merrett: And you can improve it - or sometimes you can, you know.

David Shuker: And of course that's a great… that's the other connection between cooking and sort of science. That is that the reason why science advances is through people doing experiments, and the reason why people create great new dishes, of course, is they do an experiment and they think "what if…" "What if I use this ingredient and that," or "What if I use these ingredients but cook them in a different way?" Then that's the creativity of it.

Paul Merrett: No, that's true. Berries was a really good, fun programme, partly because I think everybody enjoys berries. I mean, there is a huge variety of berries and there's a berry for everybody. I can remember, well, sitting in pick-your-own fields when I was a young lad eating huge amounts of strawberries, and they're really, really good for you. They're very high in vitamin C.

David Shuker: …very high in vitamin C. I mean, some of the berries which I enjoy, I mean I love blackcurrants, for example. I mean, my mum for years has made blackcurrant jam, and my father used to grow loads of blackcurrants - great flavour, great distinctive flavour, great deep colour, but full of vitamin C. And there are other berries like that. The great thing about berries is that they definitely contribute to the sort of healthy, balanced diet; you know, a portion of berries is going to be one of the five a day in a healthy, balanced diet.

Paul Merrett: Yes, I mean that's a pretty pleasant rule to have to live by.

David Shuker: Absolutely. I mean, it's quite different from thinking that if something's good for you it has to taste or look disgusting like cod liver oil. It's not like that. With something like berries, they can be a real pleasure. And, in season, they look good in the garden; it's a pleasure picking them, I can remember going blackberrying, for example, as a kid.

Paul Merrett: I still do, yes.

David Shuker: You end up with all those, all that wonderful colour on your fingers. But, of course, what's a great thing about them is, because you can eat them raw as you go along you think, well, sort of five berries for the bag and one for the picker kind of thing, you know.

Paul Merrett: Or the other way around. I think one of the great things about blackberries is don't… or about berries is don't keep them in the fridge - eat them warm; the flavour is much, much better. It seems to close them up when they're in the fridge, it loses the full sort of sun - you can't taste the sun in them.

David Shuker: Yes, remember that. I mean, it's all… at the time when the berries are on the plant or on the bramble, you know, it's alive and the moment you pick it, of course, it's no longer connected to the plant and then it begins to change. I mean, ultimately, if you leave it long enough it goes off, so you're absolutely right. I mean the great thing about having fruit, especially growing in the garden, is you can really pick it - harvest it - when it's fresh.

Paul Merrett: Yes. I reckon we made the ultimate berry pudding. We made a summer pudding which is a good English dessert but it's also… I mean every single berry you can think of goes into a summer pudding, it's one of those real classic puddings that's got to be really, really good for you I'm sure. The way we approach recipes with the programme is that I sit round a table with the guys at the BBC and we throw around lots of ideas, and they'll say, "look, here's the subject for the programme," and my job is to then go away and come back with the recipes, or to come back with lots of suggestions.

And when we did Berries I came back with a muffin recipe and I suggested that we piled it full of berries and baked it off, which I thought was a great idea and so did they. But word came back from you that we shouldn't have bicarbonate of soda in the recipe. Can you just explain why that was your advice?

David Shuker: Well, one of the interesting things about berries, particularly something like blueberry which has got this very highly coloured pigment in it, it turns out that the colour of that pigment depends very much on the acidity or the alkalinity of the mixture that it's in. Now, since bicarbonate of soda is actually slightly alkaline, that would actually, when you baked it, convert that beautiful deep blue colour into a sort of rather horrible green colour. You'd still get… the muffin would rise, you'd still get what you wanted out of it but you'd lose that wonderful advantage. So the way you can do it is that you can use a different raising agent, and that is baking powder, which still contains the bicarbonate to give you the carbon dioxide that you need for the raising, but it also contains some acid which actually helps to produce the CO2 but also makes sure that you keep the colour of the blueberries.

Paul Merrett: And what's the acid that it contains?

David Shuker: The acid? What you put in there is a little bit of citric acid, which is the same acid that you get out of citrus fruits.

Paul Merrett: And that's added to … all baking powder contains that?

David Shuker: Yes, it's a sort of …

Paul Merrett: And is it to balance the alkaline, is that why it's in there?
David Shuker: It's to give you something which will balance the alkalinity of the bicarb but will also, when you heat it, give you a chemical reaction which rapidly gives you carbon dioxide, which is what you need for the raising.

Paul Merrett: So, if you had bicarb in your muffin mix, is it going to make that pigment bleed out into the rest of the mix or is it just going to change the colour?

David Shuker: Well, it would probably because, as the berries tend to break up a little bit, it would bleed out. But the main thing was that, as soon as that alkalinity, as soon as that pigment got exposed to the alkalinity then it would change the colour.

Paul Merrett: So if you popped a blueberry into a bicarb solution you'd expect it to…

David Shuker: You'd see a colour change, yes.

Paul Merrett: That's amazing isn't it? You see you do all that, you go right through your cooking life without realising any of that. Well, to find out more about the science of food and to get the recipes from the series, and more of David and I chatting science, you should visit our website at I'm Paul Merrett and I've been talking to David Shuker of the Open University. The producer was Michael Brodbin. This is a BBC Worldwide Production for the Open University.





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