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Cooking with chemistry


In Short
  • Molecular gastronomy puts accepted wisdom to the test 
  • Classic taste combinations share similar aroma molecules 
  • Heat from the bottom for the perfect soufflé    

Maria Burke captures the essence of molecular gastronomy.

Top-rate chefs aspiring to a Michelin star or two, dinner-party throwers struggling with their soufflés or first-time cooks boiling an egg may find molecular gastronomy (MG) the answer to their prayers. Apparently, MG is not food science by a grander name. It is the science of cooking as practised at home or in restaurants. In more impressive terminology, molecular gastronomists define their discipline as the application of scientific principles to the understanding and improvement of small-scale food preparation.

The term molecular gastronomy was coined in 1988 by the late Nicholas Kurti, a renowned low temperature physicist from Oxford University, and Hervé This, probably the only person in the world with a PhD in molecular gastronomy. Kurti became interested in applying his scientific knowledge in the kitchen after he retired, and together with This, organised the first MG workshop attended by chefs, scientists and food writers in Erice, Sicily. Now held bi-annually, the next one will be in 2004. 

This runs the 'gastronomie moléculaire' group in Jean-Marie Lehn's lab at the College de France in Paris. To those who question whether molecular gastronomy is a serious subject, This answers: 'Science is the exploration of the world. Culinary activities are part of our world. Hence there is some legitimacy to apply some scientific knowledge to this field. And if molecular biology is a research activity, why not molecular gastronomy?'. This, who teaches molecular gastronomy in many French universities, reports a growing popularity in the subject. Until recently, he refused to take on students, believing they would not have a job later. 'But now the success of MG is so tremendous that I see that people could have a background in MG and a job later in the food industry or in research.' 

This runs a network of 'culinary teachers' in France who organise workshops. He guides their research and circulates results to the rest of the network. He is also involved in a monthly seminar on MG where chefs, teachers, scientists and food industry representatives discuss culinary matters like how to avoid cracks on macaroons. This also publishes columns in a range of magazines including the French edition of Scientific American, the chefs' magazine Thuries, the food industry magazine Process and La cuisine collective (read by cooks in schools, hospitals and other institutions). 

'With Nicholas [Kurti], we decided to make molecular gastronomy a particular discipline because we realised that there was a growing gap between food science and home-cooking', This recalls. But this has not always been the case. In the 17th and 18th centuries, cooking prompted many fascinating experiments by the pioneers of food science. Antoine Lavoisier (1743-1813) was interested in measuring the density of stock and how much solid gelatinous matter it contained. Justus von Liebig (1803-73) was another keen to rationalise stock-making while Eugene Chevreul (1786-1889) explored the chemical properties of fats. 

But gradually scientists moved away from the kitchen into large-scale industrial labs, leaving cooks to depend on cookery books for inspiration. However, as This points out, these books contain many mistakes. Take frying a steak, for example. Many cooks attribute the browning of the meat to caramelisation. In fact, it's mainly down to the Maillard reaction between amino acids and carbohydrates. 

Molecular gastronomists believe that cooking would improve if cooks understood more about the processes involved, abandoned the misconceptions of the past and embraced improvements based on rational models. How many amateurs have watched dejectedly as yet another soufflé has failed to rise? The key, according to This, is to heat the soufflé from the bottom because evaporating water pushes the other parts of the soufflé upward, and to whip the egg whites as much as possible to achieve maximum firmness. 

A soufflé is based on a viscous preparation, for example a Bechamel sauce made of butter, flour and milk, to which is added cheese, egg yolks and whisked egg whites. It used to be thought that soufflés rose as the air bubbles in the egg whites grew bigger as they got warmer. However, This has measured the temperature and pressure inside a soufflé and calculated that the bubbles can swell by 20 per cent at the most whereas soufflés can double in volume. 

In fact, the soufflé rises as water from the milk and yolks evaporates, and rises to the top of the soufflé, pushing the layers of mixture upwards. This means that heating the container from the bottom produces the best results. He has also found that the stiffer the egg whites, the more the soufflé rises. The firmer egg whites have a greater volume to begin with, but the firmness of the foam also prevents the bubbles from passing quickly through the soufflé and escaping; slowly rising bubbles are better at pushing up the layers of mixture. 

In the beginning, This' work focused mainly on investigating culinary proverbs, old wives' tales and accepted practices. His notebooks now contain more than 10,000 of these so-called 'precisions'. Is it true that potato slices in a potato salad are more tender when they're put in the dressing when hot (nobody knows for sure yet)? Should women not make mayonnaise when they have their periods (false; and yes, he has tested it scientifically)? 

New recipes
Improving on old recipes is one aspect of MG, but what about inventing new ones? This developed his unappetisingly named 'chocolate dispersion' using the theory of emulsions, but don't let this put you off. First, melt some chocolate, then wait until the temperature is below 61°C. Add the melted chocolate to egg white while whipping the mixture. Finally, place in a microwave oven for one minute. The initial dispersion of cocoa butter becomes a semi-solid mass, or chemical gel, on heating - like a chocolate cake without flour. Using a microscope, This has studied how the protein network traps the chocolate droplets, resulting in a gellified emulsion. The chocolate is dispersed twice: once in the emulsion and once in the gel. The resulting cake, he says, has a powerful aroma of chocolate - released by the high temperatures - and a 'very tender texture'. 

Molecular gastronomists can also use their chemical expertise to modify the taste and texture of dishes. Appropriate amounts of 1-octen-2-ol or benzyl trans-2-methylbutenoate, for example, give a wonderful mushroom taste to dishes, if wild mushrooms are not available. Call it cheating but adding drops of vanillin solution to a cheap whisky will produce a version with the 'round' taste of an expensive malt. It produces a similar effect to the slow reactions that occur during ageing in wood barrels where ethanol reacts with lignin to form various aldehydes including vanillin (4-hydroxy-3-methoxybenzaldehyde). 

Or what about revamping kitchen equipment? Chemists might not realise it, but apparently labs are full of potentially useful hardware for cooks. A Buchner funnel, for example, produces a much clearer stock than a normal sieve. Ultrasound boxes make emulsions in seconds. Or what about using a reflux column over a pan rather than a lid because it retains flavours more effectively? Meanwhile, This is working with the Institut für Micromechanik in Mainz, Germany, on a prototype of a machine that makes dishes from a 'calculus of recipes'. 

First introduced in December 2002 at the XVIth Congress of the European Colloid and Interface Society, this method uses letters (G for gas, O for liquid fat, W for aqueous solution, S for solid) and connectors such as / which denotes dispersions and + for mixture. This explains: 'Playing combinatorially with these symbols generates formulae that describe globally, and not locally, physical systems. And changing these systems can be described with a formalism similar to the chemical one'. For example, whipping cream to make whipped cream could be described as: 


O/W + G _____> (O + G)/W

 

Science in the kitchen 
Thanks to his collaboration with molecular gastronomist Peter Barham of Bristol University, chef Heston Blumenthal now uses a wide range of 'scientific' equipment in his kitchen - all purchased from a laboratory, rather than a kitchen supplier. Blumenthal's kitchen at The Fat Duck in Bray, Berkshire, includes temperature-controlled water baths to cook fish and some meats; a vacuum still to extract flavours from herbs and stocks before they are lost to the environment; and plenty of temperature probes. 

It seems that collaborations with chefs are vital. The advantages for the chef are clear: new dishes, new ways of preparing existing dishes, new techniques. 'For the chef, new horizons open through the understanding of some of the physics, chemistry and psychology of food', says Barham, a physicist and author of The science of cooking. 

But the scientist has much to gain as well. Imagine a scientist working on pigments, says This. 'Can you imagine how useful it would be to have a collaboration with Rembrandt, a guy who knows from empiricism much more than the scientist has ever observed?' This collaborates extensively with French chef Pierre Gagnaire (who runs Restaurant Pierre Gagnaire in Paris) and gives him one 'invention' a month, which Gagnaire puts on his website. 

For a scientist, there are many challenges. Barham comments: 'Chefs have discovered empirically a wide range of techniques and dishes that are remarkably successful. However, to date there has been very little understanding of why and how these all work, leaving a gold-mine for the enthusiastic scientist'. 

Barham has collaborated with Blumenthal for several years now, after Blumenthal phoned him to ask why chefs add salt to water when cooking beans. Some cooks say that it keeps green beans green; others suggest it raises the boiling point so the vegetables cook faster; some say it prevents vegetables going soggy and a few suggest it improves the flavour. There's no good reason, Barham told Blumenthal. The water's acidity and calcium content alone affect the vegetables' colour. Although adding salt to water does increase the boiling point, the effect is negligible. Vegetables go soggy if they are cooked too long regardless of adding salt. As for taste, little or no salt will diffuse into the vegetables during cooking; and a green bean cooked in salted water will retain on its surface less than 1/10,000th of a gram of salt, which is undetectable to most people. 

'My collaboration with Heston is like that with any other scientist', Barham explains. 'We talk often and usually the conversation quickly veers away from the original objective but always new ideas are sparked off.' For example, an original chat about rehydrating dried beans got around to heat transfer; the physics of diffusion applies in both cases. The result was 'the perfect way' to cook lamb to produce tender and juicy meat: keep the temperature at 58°C throughout the meat. After much experimenting, Blumenthal achieved this by turning the meat constantly on a frying pan kept just above 100°C for over an hour. 

Why 58°C? Over 55°C, collagen dissolves into gelatin, but at much higher temperatures they wind up into tight, dry balls. Barham says: 'On the bacteria front, you can kill most nasty bacteria by heating for a long time to a temperature above 57°C. However, when Heston cooks his lamb he takes great care first to take a blow torch to the outside, thus quickly killing any surface bacteria. He also makes sure his staff work in as sterile an environment as possible; they always wear latex gloves and never directly handle the meat'. 

Ensuring that developments in food preparation at the 'gastronomic' level filter down into the domestic kitchen is another objective of the MG community, according to Barham. He compares it with the effect of Grand Prix racing on the motor industry. 'Many developments in car safety and performance, such as ABS brakes and traction control, have been developed by the top racing teams but are now widely used in even the most basic production vehicles. Similarly, we believe that developments in the top restaurants, such as new cooking methods, and new and healthier dishes, will filter into the general food industry.' 

Weird combinations 
A big issue exercising molecular gastronomists at the moment is what determines overall appreciation of food. Why do people like some foods and hate others? Why are some flavour combinations good and others bad? Scientists now know that in several (but not all) cases where two flavours go particularly well together, they have an important aroma molecule in common, explains Barham. Both flavours probably have several hundred separate molecular components, but if only one component is common, then it seems the flavours will taste good together, such as fish and chips, and strawberries and cream. By looking at lists of molecules present in various foods, scientists can suggest new combinations. Barham insists, for example, that garlic and coffee works surprisingly well. 

So it seems that MG should benefit everybody who cooks. But This believes it could also serve to end the bad public image of scientists as well. 'If we can show that the technical part of cooking is just chemistry and physics, the public will have to conclude that sciences are not bad. In fact, they will be able to make useful distinctions between science and the applications of science, the responsibility of which rests with those who use it.' Well, the proof of the pudding is in the eating. Chocolate dispersion anyone? 

Source: Chemistry in Britain

Acknowledgements

Maria Burke is a freelance science writer based in St Albans. 

Further Reading

  • H. This, Angew. Chem. Int. Ed., 2002, 41, 83. 
  • Peter Barham, The science of cooking. Heidelberg, Germany: Springer Verlag, 2001. 

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