By Kim Maxwell
Meet the man who holds the Guinness World Book of Recordsfor making ice cream, from fresh ingredients, in 19 seconds. He is Peter Barham, a visiting professor of Molecular Gastronomy at the University of Copenhagen and author ofThe Science of Cooking.
Peter's practical cookbook draws on physics to explain how recipes work. To find the scientific reasoning behind cooking and baking techniques, Peter has worked closely with chef Heston Blumenthal of The Fat Duck, a well known restaurant located in the village of Bray, Berkshire, about an hour’s train ride from London. Peter also lives west of London, in Bristol, where he works as a professorial teaching fellow in physics at Bristol University.
Another of Peter’s passions is visiting Cape Town’s Robben Island penguin colonies as a University of Cape Town Zoology research fellow. Flexible silicone flipper bands used in penguin research identification are one of his innovations.
As a physicist, how did you get involved in cooking?
When I finished my PhD, I suddenly had time for a hobby. A cookery book arrived in front of me with some lovely recipes for cakes. When I tried the recipe for a Genovese sponge—mixing whole eggs with sugar until a stiff foam forms—it was a disaster. I wondered what should have happened. I eventually decided to write a cookbook that worked the method backwards, based on the scientific principles of what should happen.
Give us an example of what you found out.
Well, take the idea that egg yolk prevents egg whites from whisking. It is fallacy that a speck of egg yolk will prevent egg white from stiffening. Cookbooks always say this but it’s not true. In science, if you want to make a stable foam, a fat (such as you find in egg yolk) will make it collapse to some extent. Beaten egg white is a stabiliser and if you add sugar to egg white, it’s easier to turn it into a stabiliser. But it’s a fallacy that specks of egg yolk in whites destroy any possibility of making meringues or Genovese cake.
The secret is that the longer you beat egg white, the more stable it becomes. So it can actually accommodate a bit of fat. Heat also makes egg white more stable. So to make my Genovese cake, I should have been told to beat the eggs and sugar together with an electric mixer for 15 to 20 minutes to create a stable foam that won’t move if turned upside down. Mix in the flour and—right at the last minute before popping the cake into the hot oven—add the fat (melted butter). The fat collapses the foam but the baking heat immediately locks the foam in so your cake won’t flop.
Can you rescue egg whites that have been over-beaten?
Yes, by adding just a tiny bit of fat—oil or melted butter—and continuing to beat until the egg mixture has the correct consistency. The fat will make the foam collapse, but continued whisking will resurrect it.
Most chefs say meat should be seared at high temperature to seal in the juices. Is this true?
No. We tested the theory. Two identical steaks were weighed before and after cooking. We found that for a rare steak there is 10 per cent weight loss through cooking, while a well-done steak loses 30 to 40 per cent of its pre-cooked weight. What searing does is change the flavour, but it doesn’t seal anything in. Heat actually squeezes liquid out of meat.
How should we cook the perfect steak?
Raw steak has tender muscle fibres. With heat, the fibres denature, shrink and become hard. This starts to happen at about 55°C. At higher temperatures the process is quicker. Secondly, when the collagen connecting the meat to the bone is heated above 55°C and for long enough, it turns into gelatine. Thirdly, browning the meat without sealing it creates new molecules not found in nature. Cooked meat has artificial molecules created by burning. So to make the perfect steak with natural flavour, chefs should cook meat at a very low temperature for a very long time—enough to denature the collagen but not to toughen the meat inside. For example, cooking a whole piece of rib-eye at 55°C for three to four hours will create medium-rare meat. Amateur cooks should not do this at home. Experienced chefs use a process called sous vide, where the steak is vacuum packed to prevent bacteria growth, and cooked in a temperature-controlled water bath. Afterwards the steaks are seared for seconds on either side in an incredibly hot pan to brown them. Steak cooked this way has no shrinkage or moisture loss.
What about adding salt to foods as you cook them?
Most people add salt to everything when they cook. Chefs say salt fixes the colour when cooking green vegetables. Or that salt is essential seasoning for cooked beans. Some cooks say salt raises the boiling point. In fact, only one of those is true: salt raises the boiling point of a pot of water but it doesn’t change the temperature significantly enough to count. No salt is absorbed by green beans or green vegetables. You can’t taste it in the food. It’s different with root vegetables, though, because they have a high starch content. They can absorb the salt in the water, as does pasta. It’s the starch content of a vegetable that determines whether salt in the cooking water has an effect on its flavour or not.
Some people complain of headaches after eating at Asian restaurants and think it’s linked to MSG. Is this true?
No. Monosodium glutamate (MSG) is also known as glutamic acid and occurs naturally in some foods. MSG, contrary to some widely-held views, is a natural substance made from soya and isn’t harmful. The taste of umami is a salty sensation caused by glutamic acid in food. Not many people are aware of the fact that the highest levels of naturally-occurring glutamic acid are found in Parmesan cheese, followed by tomatoes. So it is actually Italian food that has the highest umami—MSG levels—not Asian food.
Now that we’re done with some myths, tell us how you achieved your world record time in making ice cream. How is it possible in 19 seconds?
If you’re a physicist in a lab, you cool any gas with a coolant. Physicists always have liquid nitrogen on tap, and it makes a great coolant because it’s a liquid that boils at a temperature of minus 196°C. We know that water turns into ice as tiny crystals form and grow bigger in time. The more quickly I can freeze the ice crystals, the smaller and smoother they become. If I take liquid nitrogen and pour it into a liquid ice cream mixture, it cools the ice cream very fast and the crystals formed are very small. My world record ice cream involves double cream, vanilla and icing sugar in a bowl. Give it a quick stir, throw in liquid nitrogen, and give another quick stir. It’s done.
How do you think the public perceives molecular gastronomy?
I think it’s a much-abused term. It is really the study of why one dish or ingredient is delicious and another is not. ‘Gastronomy’ refers to tasty food and ‘molecular’ to basic analytical science. That’s why it makes sense to scientists but doesn’t work as a restaurant title. Most chefs don’t like the term because they’re cooking good food anyway. Besides, through trial and error they’re already using the best bits of science available to them.