Culinairy Arts Blog Cooking with love & science an insight into Molecular Gastronomy continues!

This week we will continue our story.however, scientific knowledge is useful, because it remains true that the phenomena involved in the kitchen (browning of the steak during cooking, thickening of the mayonnaise sauce during making, Etc.) Are chemical and physical transformations? As science is invited in the culinary curriculum, let's first look for the main phenomena that have to be considered. Ten only should probably be taught in all culinary schools: 1. salt (S) dissolves into water (W)2. salt (S) does not dissolve into oil (O)3. oil (O) does not dissolve into water (W)4. water evaporates at every temperature, but boils at 100°C5. most food contain primarily water (or another fluid)6. food with no fluid is hard (generally)7. some proteins (eggs, meat, fish) coagulate8. collagen dissolves into water when heated to more than 55°C9. most food are disperse systems10. some chemical processes (Maillard, Strecker, oxidations...) generate new flavours. Ten easy sentences! Let's consider on one example, pastry making, how these ideas can be put intopractice. No recipe! French pastry chefs usually distinguish puff pastry, on one hand, and sablée or brisée pastry on the other hand. Let's focus here on the last two. A survey of classical French recipes of brisée pastry orsablée pastry show that, according to books, either the ingredients make the difference, or theProcesses, but all this is not very clear, because various authors contradict themselves. Only the resultCan make all pastry makers agree: sablée pastry is more "sandy" than brisée pastry.In all recipes of brisée pastry and sablée pastry, dough is made from butter (b), flour (f) and water (w)(plus some minor ingredients, such as salt, that play an important role for flavor, but not for doughmaking). There are six possibilities of mixing: bfw, bwf, wfb, wbf, fwb, fbw. But looking at the resultsshows that only two possibilities are different: (b+f)+w, and (f+w)+b. Why?The answer is given in the experiment that was proposed as early as 1754 by the Italian chemistJacoppo Beccaria: in order to understand the composition of flour, he mixed it with water, forming adough; then he pressed gently the dough in water, recovering a white powder (starch) and a chewymass (gluten). Figure 1. When flour is kneaded with water, then pressed in water, a white powder (starch, onthe left) separates from a chewy mass (right) made of some particular proteins (gluten).This experiment demonstrated that flour was made from starch and gluten. Observing the doughduring the experiments also shows very clearly that gluten is a viscoelastic network where starchgranules are trapped, like fishes in a net (three dimensional). Viscoelastic? It means that gluten hassome elasticity, like rubber, but also that it flows, slowly, with some viscosity.If butter is added to dough, it divides into particles that are trapped in the same gluten net, and thisdough leads to a robust brisée pastry after cooking.But if butter is first mixed with flour first (before water is added), then starch granules are coated withfat, and this fat coating hinders gluten formation, so that sablée pastry is made. Figure 2. There are two ways of mixing wheat flour, water and butter (top): if flour is kneadedfirst with water, a gluten network is formed, into which fat is dispersed, and a "brisée" pastry isobtained (left) ; but if the flour is first mixed with butter, no gluten network can form whenwater is added (right), and "sablée" pastry is formed. How much starch can be put into butter?A model where starch granules are considered as disks that form a regular tiling leads to aproportion of 1 part of butter for 3 parts of starch. When a 3-dimensional model is preferred, a1/1 proportion is calculated.Let's now come to the proportion of the various ingredients in dough. A small calculation can be madeto understand how much flour can be mixed with a certain quantity of butter. Let's consider first thetwo dimensional case of a square packing of circular flour granules having all the same radius.Imagine that the radius of these granules is equal to 1. Then the area of each granule is _, i.e. about3, and the area of the part of the squares that is not covered by starch is (2x2) - 3 = 1. It means thatdough can be obtained with a proportion of starch: butter of 3:1. This is an order of magnitude only, asa closer packing can be obtained with disks placed in a hexagonal packing or with disks of differentradius.Of course, dough is not two-dimensional, but the same question in three dimension leads tocomparing the volume of spheres (4 _/3_4) and the volume of cubes outside these spheres (2x2x2 -4 = 4). Here again, the correction for close packing would not change much the result.One important assumption, in all these calculations, was that disks or spheres have all the sameradius. Two millennia ago, the Greek mathematician Apollonius of Perga asked if it was possible tocover completely a plane with disks of any size, and in 1934, the American mathematicians M.Kaushik and M. Warren demonstrated that it was indeed possible.