Science Interviews


Mon, 27th Jun 2016

Fry me up a perfect fish

Alex Rushmer, Hole in the Wall, Dr Sue Bailey, London Metropolitan University

Listen Now    Download as mp3 from the show Science meets MasterChef!

How does temperature affect flavour, why does brown food taste better and blowtorchhow 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 Iíve 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. Thatís crucial to it.  Before we do anything with it we salt it, thatís 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 Iíve had in restaurants in the past. Not yours, because Iíve not dined in your restaurant but the fish is dry and you think, Uh I donít like that.  Why are you drying it?

Alex - So weíre drying it to caramelize the outside, weíre not drying the inside of the fish. Itís a very delicate cure that we put on the outside. A symptom of overcooking fish is a fish that feels dry in your mouth, thatís what weíre 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 - Weíve got one right here

Chris - The same thing youíd see in your garage actually, OK. Well donít burn my microphone or my worktop.

Alex - Iíll try not to.

Chris - Here we goÖ Alex is literally blowtorching the surface of the fish. So weíve got the fish sitting in an oven tray and each piece is 10-15 seconds on each piece Iíd say?

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

Chris - Itís just turning, isn'tí it? Little tiny black spots here and there on it like dark spots and itís just sort of crisping up. And youíre done?

Alex - Thatís it.

Chris - Now what?

Alex - Itís as easy as that. Weíve got a pan on the heat here. A very, very high heat usually for fish cookery. Weíve got a little film of oil in there and the fish goes straight into the panÖ

Chris - And youíre actually holding the fish down, youíre actually pressing that down into the oil?

Alex - Iím holding it down very, very gently. What you donít want to do with meat or fish cookery is apply a lot of pressure to it. Itís 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 itís in the pan or they mess around with it. Itís something that you actually want to do is leave it alone, let it cook, let it do itís thing.

Chris - Right Iím going to leave you alone and let you do your thing, do what you do best. Iím 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, whatís going on chemically is that the protein of the fish is beginning to denature. And whatís happened is that you really donít 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 itís just enough to brown it and give the Maillard browning, the browning reaction which you saw. And now what heís 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, youíd get not very juicy, not such nice fish as heís going to produce.

Chris - Youíve 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 youíve 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. Itís whatís known as its tertiary layers, and it begins to unfold, and then it begins to firm upÖ

Chris - The protein changes shape?

Sue - The protein changes shape.

Chris - Thatís why we get sort of colour change and the texture change?

Sue - Thatís 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 thatís what give you a lovely caramely, smokey, flavour, and also the visual effect that youÖ

Chris - Ah, so thatís the good taste?

Sue - Thatís the good taste, yes.

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

Sue - Absolutely so. Thatís exactly right.

Chris - How are you getting on Alex?

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

Chris - Heís going to put butter in - is that a good idea Sue?

Sue - Oh yes for flavour, yes absolutely. What itís going to do is give you a bit more caramelization on the fish and when you serve it itís 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, heís now just making sure that itís finished nicely and tastes perfect.

Chris - Thatís quite a big knob of butter.

Alex - This is the other thing that you donít see in home kitchens and awful lot is the amount of butter that we use in a restaurant kitchen.

Chris - And Iím liking this. Youíve got that lovely technique of flicking the melted butter over the top of the fish as it goes.. Is that so you donít have to fiddle with it and turn it over like you were saying?

Alex - Thatís exactly it. So Iíve 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 thereís 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 itís also browning off the top of the fish as well.

Alex - Itís browning of the top of the fish and the butter is foaming as well. Thatís how we know that the temperature is right. What we donít 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 youíve got 30 seconds to plate that up Alex. Weíll just ask Sue - why was the butter all foamy like that?

Sue - Thatís partially because of the salts and a little bit of the water.

Chris - Itís sort of boiling away and driving steam inside the butter?

Sue - Itís slightly boiling away driving some steam away making sure that itís 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 itís only 40 degrees in the middle, how do we know thatís safe to eat?

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

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 centigradeÖ

Chris - Or above?

Sue - Or above to make sure that itís safe to eat. And so Iíve just seen him prodding it now - I donít know whatís happeningÖ

Chris - Whatís 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. Iím just going to wiggle overÖ

Chris - I canít wait. Can I help myself to one of these forks Alex?

Alex - Of course.

Chris - Iím always so jealous of the fancy guys on tele when the do this. So Iím going to have a little bit - here we goÖ Oh, thatís melt in your mouth.

Georgia - Oh here we go.

Chris - I guess thatís what you get paid for Alex. Is that what youíre 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 - Thatís it. With cod youíve got a fish with fairly large flakes which you do want to fall apart. You donít want them to be stuck together. I think thatís part of the process of the denaturation of the proteins.

Sue - Yes absolutely. Whatís 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.



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