From Crispiness to Crunchiness

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I want something that's crunchy, crispy, chewy in the centre, tender, or frothy. ... I want a pale green or some dark red, a smell of undergrowth and a nice mushroom taste. ... To cook for a gourmet is to try and optimise many parameters such as texture, colour, and smell, so that all their senses are in fusion while they taste the dish. The gastronome cook is looking for perfection in the dishes he creates.

But how to achieve this perfection? This universal question reaches far beyond our stoves and finds an answer in the understanding of the systems we manipulate in our kitchens. If we can indeed understand how a system is structured to the point that we can predict how it will behave in a given situation, then we are able to optimise it. The way to do it seems, then, all mapped out: to observe, experiment, and analyse, take a step back and design a model, try it out in a real-life situation, and, in the most favourable case, identify general rules.

Isn't this the scientific approach? Could science help these gastronomes in their quest for a taste so exact, a harmony so perfect, a texture so faultless that they overwhelm the gourmet's senses? We thus have to lean over our saucepans, and a bit further still, over the microscopic and molecular scales, to understand the numerous physical and chemical reactions and processes that lead to a meat cooked but tender, a puffed-up sponge cake, a soufflé full of air, a dish of crunchy vegetables. It is from this approach that a new discipline, molecular gastronomy, was created by Hervé This and Nicholas Kurti in 1988, and it is also here that science and gastronomy met.

As a second-year Ph.D. student, but even more as somebody who is passionate about materials science and a keen cook in his spare time, I can only immerse myself in this discipline that combines my two passions best! I have a traditional scientific background and did a DEA (equivalent to an M.Sc.) in materials science at Pierre and Marie Curie University in Paris. Looking for a placement in a research lab at the end of that year, I got in touch with This, whom I heard of thanks to his book Les Secrets de la Casserole and his TV programme Toque à la Loup.

We hit it off straight away, and we designed a project that was suited both to the requirements for the validation of my DEA and to our interest: understanding what is going on in our saucepans to better control what we are cooking! And thus, at the Laboratory for the Chemistry of Molecular Interactions at the Collège of France, I spent three unforgettable months in the fascinating life of This, a generous man whom I genuinely thank for all that he's done, and is still doing, for me.

The culinary question we asked ourselves was the following: How does one explain the origin and mechanisms of the crunchiness of certain foods? To obtain crunchiness in cooking, we very often have to start with a preparation that is initially soft, such as dough, a crêpe batter, or potato slices, and heat it up to obtain a crunchy puff pastry, a brittle crêpe dentelle, or some crisps. So what's happening during the cooking process?

Each of these raw foodstuffs contains some water, and to heat them up is to eliminate some of this water in the form of vapour. Evaporation makes the material more and more rigid until it becomes brittle. This transition from a more or less viscous liquid state, or from a ductile solid (that can be manipulated with fingers), to a state that is both solid and fragile suggests a phase transition. Furthermore, for a solid to break, some fissures must first be able to propagate from one end to the other. We thus hypothesised that "rigid paths" were forming at the heart of aqueous systems during cooking thanks to a process called percolation, allowing the propagation of a fissure. The material breaks; the food crunches! Here would be all the difference between a cooked but soft crêpe and the definitely crunchy crêpe dentelle.

So we studied sugar syrups, mixtures of saccharose and water, as these also change from a viscous system to a brittle solid depending on water concentration. Indeed, if we take some samples while cooking, we obtain syrups that are thicker and thicker once cooled, so much so that you can eventually manipulate them with your fingers, until the syrups become brittle. We followed the evolution of this viscosity, then elasticity, and our first results indeed point toward a phase transition with percolation between the molecules of saccharose. Thus, when we eliminate "enough water" through heating, that is when we reach the threshold for percolation, the saccharose molecules "see each other," and form clusters, which organise themselves into a real network. A fissure can then propagate from one end of the material to the other: hence the brittleness. We are next hoping to transfer this model to more complex food systems, such as batters for crêpes or puff pastry, in which dozens of chemical compounds come into play and affect the formation and properties of these networks of rigidity.

Even though I am now carrying on with these experiments, I do so during my free time, given that my Ph.D. is rather far away from the saucepans. I am studying ferroelectric crystalline solids through the diffraction of x-rays and neutrons in the CNRS Structure, Properties and Modelisation of Solids Laboratory at l'Ecole Centrale of Paris.

So how does this relate to molecular gastronomy? The scientific motivation and approach are in fact the same: to understand matter, study the inside to explain the external behaviour and properties. What difference in fact is there between chewing gum and a polymer? Both of them present elastic, then plastic, behaviours before breaking under the strain. And why should we separate the study of amorphous cast sugar and silica glass? The two are so similar that in movie stunts, numerous are the actors that go through windows made of saccharose! Although culinary, foodstuffs are before all materials, subject to the same rules and principles.

My professional objective is to become a lecturer in materials science. Besides my research and my first steps as a teacher, I also take part in numerous events related to molecular gastronomy such as public conferences, science festivals, and visits to catering schools. What can be better than melting your passions and work into one? And what can be more satisfying when one wishes to teach than teaching the public?

In addition to helping cooks understand the mechanisms that are happening while they are cooking, and bringing them closer to the perfect recipe, molecular gastronomy is an excellent way to democratise science. So three cheers for cookery and three cheers for physics and chemistry!

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