Culinairy Arts Blog Cooking with love & science an insight into Molecular Gastronomy The Next Chapter

Figure 3. The model of figure 2 can be improved by considering that starch granules have alldiameters, instead of being disks of the same size. Using these new shapes, it has beendemonstrated in the 30's that a plane can be fully covered. The implication of dough would bethat any proportion between 0 and 100 % starch can be used in order to prepare "sablée"pastry. Of course, the consistency would change!This means that sablée pastry could even be obtained by using a proportion of flour: butter equal to1:0. Of course, this is only mathematics, not cooking, but experiments shows that dough can even beachieved with a 30:1 proportion; of course, its consistency is not the same as with 1:1 proportion, andthe final product looks more like chapati bread than like traditional sablée pastry. Anyway, theconclusion of this survey is that recipes are useless, from the technical point of view, as reasoning canexplain them, and even explain how much liberty the cook has.On the contrary, no calculation can ever tell if lard is better than oil or butter, if chestnut flour is betterthan rice flour, etc. What does cooking mean? Having shown that we do not need fixed recipes, let's come to the main point of culinary craft: cooking.What is cooking? Let's consider first cooking eggs and move later to meat, fish and vegetables orfruits.In boiling water, an egg white looses its transparency and yellow color to become white; it loses itsliquid consistency to become solid. Why?The preliminary experiment of heating an egg white (about 30 g) in a pan shows that egg white ismade of two parts: first water, forming a white smoke over the pan, makes 90 percent of the white; inthe pan, after evaporation of water, a yellow solid sheet is primarily made of proteins (about 3 g).As water does not coagulate, it has to be admitted that proteins are responsible for the coagulation ofegg white when heated. Why? Chemical studies have shown that proteins are like coiled opennecklaces; the pearls are amino acid residues, of which two major kinds exists: hydrophilic ones andhydrophobic ones. In water, proteins reduce their energy by coiling so that the hydrophobic segmentsof the protein are in the centre, surrounded by hydrophilic parts.These proteins do not retain their fixed coiling, as water molecules are perturbing the coiling. Whenthe kinetic energy associated to heat is greater than the coiling energy, proteins uncoil, and exposetheir thiol groups -SH of cystein amino acids; under oxidizing circumstances, these groups react toform disulfide bridges (-S-S-) that link proteins together. Figure 4. When proteins (with hydrophobic core, in red, and hydrophilic parts, in pink) uncoil,they can link because sulphur atoms make "disulfide bridges". Linking of proteins isresponsible of the formation of a protein network, in which water from egg whites are trapped.In the heated egg white, linked proteins form a network where water molecules are trapped. This iscalled a gel (more precisely a chemical gel, as disulfide bridges are strong forces, and chemical gelsare not reversible). Figure 5. A model of egg white coagulation. Many proteins of egg whites are coiled, becausethe inner part is hydrophobic; being dissolved in water (egg white contains 90% water), theproteins coil spontaneously, so that hydrophilic parts are in water, as hydrophobic parts areburied. When heated, the energy of movement of the molecules induces an uncoiling ofproteins ("denaturation") and, subsequently, a coagulation of egg whites, due to chemical linksbetween uncoiled proteins (bottom). Of course, such description is simplified, as, in particular,proteins do not extend like threads.How much does this theory hold? An experimental check is to ask the question: why are proteinscoiled? The answer is: because they are in water. Therefore in something else than water, theyshould coil differently and perhaps coagulate also.Let's make the experiment of adding ethanol to an egg white: when the ethanol concentration isenough, egg white coagulates. Of course, this can be done with something else than ethanol, such asvodka, or cognac...Let's go on with experimental tests. What if acid were added to egg white? Is it true that acids "cook"fish, like in fishes "à la Tahitienne", or in cebiche? Of course, there are theoretical reasons to get aresult, as proteins have some amino acids residues whose electric charge depends on pH (a measureof acidity or alkalinity, between 0 and 14). And when an egg is put into vinegar, there is first dissolutionof the shell, then a slow coagulation of the egg, producing a strange egg, after about one month. As"one century years old eggs" are obtained in China by putting eggs in a mixture of clay, straw and limeor ashes (containing potash, i.e. an alkali), we called our "acid cooked" eggs "minus one century yearsold eggs".Are they "cooked"? Not if we follow to the definition given by the dictionary, according to which cookingis a transformation induced by heat. This is why, in France, after an email poll for more than 1300people, we decided for the new word "coction", to describe non thermal induced coagulation.Finally is the coagulation theory true? Not completely, as it is only a theory. It does not explain, inparticular, why hard boiled eggs are tender when cooked less than 10 minutes, and why they have arubbery white when cooked longer.The theory is not precise enough to explain this fact: we have to use a more complex explanation,considering that egg whites are made of a lot of proteins, having each a special denaturationtemperature. The first one, for ovotransferrin, is 61°C: at this stage, the egg white should be verytender because only one net is trapping water molecules. At temperatures higher than 70°C, otherproteins coagulate, making a second gel in the first, the consistency becomes harder, etc. As the yolkis concerned, the first transition is about 70°C.Hence the question: what would we get if we cook an egg at only 65°C? The result is a veryinteresting egg, whose consistency does not depend on cooking time, but only on temperature.Here is, for example, a 65°C egg: Figure 6. An egg cooked at 65°C for more than two hours. As fas as thermal equilibrium isreached, the final state does not depend on time, but only on temperature. At 65°C, the eggwhite is slightly coagulated, but the yolk is still liquid. This new egg has nothing to hard boiledeggs, fried eggs, poached eggs, etc. It's an "egg at 65".