Cake theory: why science is excited by food

How do you bake a cake? Most probably not the way Peter Barham does. If you beat your eggs, for example, rather than denature the protein to expose the hydrophilic molecules, or if you let the cake bake in the oven, rather than allow the egg protein to cross-link chemically, then you are a very different kind of baker to Barham.

This professor of physics at Bristol University has a zeal for understanding the science behind cookery processes. It’s an enthusiasm that began almost four decades ago, with a kitchen failure. In 1975 his wife gave him a cookbook after he finished his doctorate – with a PhD, logic suggests, you should be able to make an omelette. “I read the instructions and followed them, but nothing worked,” Barham says, still a little indignant. The only way he could improve his cooking, he concluded, was to “understand what [the cookery writers] actually meant you to do”.

If, unlike a published scientific experiment, a recipe couldn’t be reproduced with the same results as the original, it was, in Barham’s view, a failure, “fluffy stuff”. So he set about a surreally detailed analysis of the recipe for a Genoise sponge, translating it into rigorous scientific vocabulary. It attracted attention in his department, not least for the success that older colleagues had in baking their own sponges with his recipe at home.

But Barham was not the first physicist to become interested in food science. In 1969 Nicholas Kurti, professor of physics at Oxford, gave a Royal Society lecture on “The Physicist in the Kitchen”. Famously, he remarked, “I think it is a sad reflection on our civilisation that while we can and do measure the temperature in the atmosphere of Venus, we do not know what goes on inside our soufflés.”

Kurti’s cause was to bring science to the fore in the cook’s mind and to reorder the kitchen as a laboratory. There were so many possibilities for ingenuity and discovery in the medium of food. Kurti had proved it in the lecture theatre, injecting mince pies with rum through a hypodermic syringe, and tenderising a loin of pork by injecting it with fresh pineapple juice, which contains the proteolytic enzyme bromelin.

The influence of this culinary scientific principle today is everywhere – in restaurants, cookery books, and on television. And contrary to popular perception it was the scientists, the Kurtis of this world, not the Ferran Adriàs, who started the trend.

In the 1970s, Barham admits, “men were scientists, women were cooks”. The dynamic began to shift in the early 1980s, when a cookery teacher, Elizabeth Thomas, based in San Francisco, had an idea to bring scientists and chefs together. If Thomas had questions in her cooking she found her husband, a physicist, was able to “offer answers”. She suggested a seminar that would “get a group of people together to start understanding these things”, and invited Kurti to be its director. This became the International Workshop of Physical and Molecular Gastronomy, held in the Sicilian town of Erice during the 1990s, until it became “too big and popular” about a decade ago and was disbanded. (Kurti died in 1998.)

Through Barham’s participation in Erice and the food science circuit, one day in the late 1990s he got an unusual phone call back at the lab in Bristol. “You don’t know me,” said the caller. “I’m a chef, and I need your help.” It was Heston Blumenthal, and his “little problem” concerned green beans. Blumenthal’s Fat Duck restaurant had a tiny kitchen at the time, and he found that if he cooked green beans in salted boiling water, as the books instructed, “he could only cook six at a time, or the water came off the boil [when salt was added]”, Barham remembers. Blumenthal had experimented and found that neither salting nor boiling seemed to be essential – “you just had to get [the beans] hot, but he couldn’t find any literature anywhere to say if [that method] was right or wrong”. Barham affirmed that the salt made no difference, and the pair began to collaborate: “We went on from there”.

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Today, Barham is not so much polymath as several people at once: expert on polymers, sometime adviser to Blumenthal, and visiting professor of molecular gastronomy at Copenhagen University. He is also besotted with the African penguin – he has just led the 8th International Penguin Conference in Bristol – and devotes much of his research to these birds.

The pressing culinary question for him now relates to the psychology of taste and flavour: to what extent does the complexity of food influence how much you like it? This is what he and colleagues in Copenhagen want to know. Other challenges have been conquered – Kurti’s soufflé question, for example, was solved 10 years ago. Faced with a problem, Barham says, “as a scientist I find it hard to believe there isn’t an answer.

“Consider a simple dish, bacon and eggs, say – rashers and a fried egg. Suppose I want to make it more fun, I might mix them together to make a soufflé and have a variety of textures with the same ingredients. Or I might make an egg and bacon tortilla, or ice cream. But to define complexity is very difficult; all you can do is say one thing is more complex than another.”

The most important phenomenon, he argues, is that increasing complexity correlates with enjoyment only up to a point. “If you can modify the complexity of food in such a way that people really like it, but because it’s so complex find it more difficult to absorb it, they will eat less of it,” he says. “We’ve done a few trivial experiments to suggest there’s something there.” The simplest example is chocolate: “if you give people Dairy Milk they’ll eat 200g – a lot. But give them a Valrhona, and they might eat 20g or 30g. By altering the quality of food, can you alter the quantity people are consuming, without them even noticing? There’s potential there for things like obesity.”

Back at home in Bristol, Barham’s wife’s original present has produced unexpected results. After a meal, Barham often serves a toffee-like dessert that comes out of the fridge cold and soft, but hardens and heats up as you suck it. “More fun still, as it melts away in your mouth, it gets cold.” Why? “Simple physics. If you take something that is a liquid and turn it into a solid, it has to give heat out. You start with a liquid sugar, and as you warm it up in your mouth it will start to crystallise, and becomes a solid. Now you dissolve that solid sugar crystal, and put heat back into it, so it takes heat away from your mouth and cools it back down.” Barham pauses, then confirms again: “Simple physics.”

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