Fry me up a perfect fish

How does temperature affect flavour, why does brown food taste better and how can a blowtorch improve your cooking? Food scientist Dr Sue Bailey and head chef Alex Rushmer have teamed up to take Chris Smith through how to fry the perfect fish.

Alex - OK. So I've got some lovely fillets of white fish here. We use cod but you could do the same thing with hake, or turbot, or halibut if your budget allows, but the process is exactly the same. The cod comes in to us, we choose the best possible fish. That's crucial to it.  Before we do anything with it we salt it, that's the first thing we do. We liberally season it with just regular table salt, we then leave it in the fridge uncovered for about three quarters of an hour to hour depending on the size of the fish. After that we rinse it, we give it 2-3 minutes in fresh cold water. Then it goes back into the fridge on blue cloth. We dry it as closely as we can, we really get both sides very, very dry. We leave it uncovered in the fridge for about 4 or 5 hours.

Chris - That may sound counterintuitive to some people why you would want to dry fish because some of the things I've had in restaurants in the past. Not yours, because I've not dined in your restaurant but the fish is dry and you think, Uh I don't like that.  Why are you drying it?

Alex - So we're drying it to caramelize the outside, we're not drying the inside of the fish. It's a very delicate cure that we put on the outside. A symptom of overcooking fish is a fish that feels dry in your mouth, that's what we're trying to avoid.

Chris - Right, so you dry the surface, then what do you do? Is that straight in the pan or is there another step?

Alex - Before we put it in a pan we blowtorch it.

Chris - Blowtorch it?

Alex - We use a blowtorch to further dry out the skin and begin the caramelization process.

Chris - Is that that?

Alex - We've got one right here

Chris - The same thing you'd see in your garage actually, OK. Well don't burn my microphone or my worktop.

Alex - I'll try not to.

Chris - Here we go... Alex is literally blowtorching the surface of the fish. So we've got the fish sitting in an oven tray and each piece is 10-15 seconds on each piece I'd say?

Alex - Yes, about that. Just enough when you see the colour starting to appear.

Chris - It's just turning, isn't' it? Little tiny black spots here and there on it like dark spots and it's just sort of crisping up. And you're done?

Alex - That's it.

Chris - Now what?

Alex - It's as easy as that. We've got a pan on the heat here. A very, very high heat usually for fish cookery. We've got a little film of oil in there and the fish goes straight into the pan...

Chris - And you're actually holding the fish down, you're actually pressing that down into the oil?

Alex - I'm holding it down very, very gently. What you don't want to do with meat or fish cookery is apply a lot of pressure to it. It's something I see a lot, especially with new chefs in the kitchen or people that cook in their own homes, is they play with the food when it's in the pan or they mess around with it. It's something that you actually want to do is leave it alone, let it cook, let it do it's thing.

Chris - Right I'm going to leave you alone and let you do your thing, do what you do best. I'm going to come over here and have a chat to Sue. Because Sue, can you tell us what Alex is up to, what is actually going on chemically in this frying pan?

Sue - Well, what's going on chemically is that the protein of the fish is beginning to denature. And what's happened is that you really don't want your fish to cook at too high a temperature, typically about 40 degrees centigrade. He cooked it with a blowtorch, that goes up to over 1,000 degrees centigrade but it's just enough to brown it and give the Maillard browning, the browning reaction which you saw. And now what he's doing is just cooking the fish very gently. Normally what happens, you have to cook up to about 110 degrees centigrade in order to get a Maillard reaction. If you did that to the fish, you'd get not very juicy, not such nice fish as he's going to produce.

Chris - You've mentioned a number of words there. Denature was one of them, denaturing the proteins. First explain what that is, and then tell us what this Maillard reaction that you've mentioned a couple of times is?

Sue - Well denaturing is what happens when you have the protein which is typically in layers, what happens is that the protein, as you heat it, denature it, the protein parts of the food begin to unfold. It's what's known as its tertiary layers, and it begins to unfold, and then it begins to firm up...

Chris - The protein changes shape?

Sue - The protein changes shape.

Chris - That's why we get sort of colour change and the texture change?

Sue - That's why you get colour change and so on.

Chris - What about the Maillard, the browning?

Sue - Right. The Maillard reaction is where you have got a reaction between the sugars and amino acids from the protein, and that's what give you a lovely caramely, smokey, flavour, and also the visual effect that you...

Chris - Ah, so that's the good taste?

Sue - That's the good taste, yes.

Chris - So that's why Alex did the blowtorch was to get lots of that Maillard reaction which needs the high temperature but now he's cooking at the slightly lower temperature to avoid destroying the quality of the meat inside? So we've got the best of both worlds, the good taste plus the good texture.

Sue - Absolutely so. That's exactly right.

Chris - How are you getting on Alex?

Alex - Yeah, I think we're looking good. There's some nice colour that's starting to appear on the side of the fish that's in contact with the pan. I think another 30 seconds or so on that side and then we'll flip it over and cook it from the other side, and we'll introduce some butter to the pan as well.

Chris - He's going to put butter in - is that a good idea Sue?

Sue - Oh yes for flavour, yes absolutely. What it's going to do is give you a bit more caramelization on the fish and when you serve it it's going to be nice and foamy, slightly golden brown, nutty flavour and, because you were cooking it before in a very neutrally flavoured oil to have the temperature right, he's now just making sure that it's finished nicely and tastes perfect.

Chris - That's quite a big knob of butter.

Alex - This is the other thing that you don't see in home kitchens and awful lot is the amount of butter that we use in a restaurant kitchen.

Chris - And I'm liking this. You've got that lovely technique of flicking the melted butter over the top of the fish as it goes.. Is that so you don't have to fiddle with it and turn it over like you were saying?

Alex - That's exactly it. So I've got the pan leaning towards me ever so slightly, probably at an angle of about 30/40 degrees. The fish is at the far side of the pan and then there's a nice pool of butter sitting just in front of me here which I can then spoon straight over the fish. You can smell it and you can smell the slightly biscuity nature of the butter.

Chris - it does smell biscuity and it's also browning off the top of the fish as well.

Alex - It's browning of the top of the fish and the butter is foaming as well. That's how we know that the temperature is right. What we don't want to do is take the butter to far and actually burn it, you end up with a slightly bitter flavour.

Chris - Right. As they say on Masterchef you've got 30 seconds to plate that up Alex. We'll just ask Sue - why was the butter all foamy like that?

Sue - That's partially because of the salts and a little bit of the water.

Chris - It's sort of boiling away and driving steam inside the butter?

Sue - It's slightly boiling away driving some steam away making sure that it's perfectly cooked.

Chris - Now talking about perfectly cooked, what can you say about the sort of food safety aspects. How do we know that that piece of fish if it's only 40 degrees in the middle, how do we know that's safe to eat?

Sue - Well, I think this is where Alex is going to use a tried and trusted thermometer which perhaps...

Chris - With his thumb?

Sue - No, no, no! I can just him wiping it off now. Because the important thing is from a food safety point of view, you need to have it at 40 degrees centigrade...

Chris - Or above?

Sue - Or above to make sure that it's safe to eat. And so I've just seen him prodding it now - I don't know what's happening...

Chris - What's the verdict?

Sue - The verdict is it is cooked.

Chris - Georgia - it looks good. Are you going to come and try this?

Georgia - I absolutely want to have some. I'm just going to wiggle over...

Chris - I can't wait. Can I help myself to one of these forks Alex?

Alex - Of course.

Chris - I'm always so jealous of the fancy guys on tele when the do this. So I'm going to have a little bit - here we go... Oh, that's melt in your mouth.

Georgia - Oh here we go.

Chris - I guess that's what you get paid for Alex. Is that what you're going for a sort of it falls apart in your mouth? It doesn't need much effort to make that fish fall to pieces on your tongue.

Alex - That's it. With cod you've got a fish with fairly large flakes which you do want to fall apart. You don't want them to be stuck together. I think that's part of the process of the denaturation of the proteins.

Sue - Yes absolutely. What's happening there is that the collagen in fish melts at a slightly lower temperature than it does typically in meat, so it typically goes at 41 degrees centigrade and the fish is cooked at 40 degrees centigrade. So, as you say, it should just flake apart beautifully but not be overcooked or dry.