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

From eggs to meat and fish After egg white, which is the simplest case, let's move to fish and meat. In both cases, some proteinsand water molecules are inside "muscular fibres", i.e. long "tubes" whose "skin" is made of a specialtissue called collagenic tissue. This tissue is indeed not woven, but made of adjacent microfibers of aspecial kind of proteins, called collagen. In meat and fish, the collagen molecules wrap around oneanother by three, forming "triple helices". And the collagenic tissue is gluing the fibres in bundles.Some bundles are even groups in super bundles, and so on. The more collagen content, the harderthe meat (fish meat contains a small proportion of collagen, hence the special consistency).When meat is cooked, proteins and water inside the cells coagulate, making the meat harder, butcollagen slowly dissociate in water, and produces isolated collagen molecules in water, that isgelatine. Figure 7. Cross section of meat, under the microscope. The yellow parts are mainly a solutionof proteins in water. They are surrounded by collagenic tissue (in red). Bundles of muscularfibers are grouped in larger batches, that are themselves grouped. Collagenic tissue slowlydissolves into water above 55°C.But the eggs experiment now shows why beef meat cooked for very long in boiling water (poor "potau-feu") are so poor, with separated, hard fibres: the inside of the fibres coagulated like rubbery eggwhites, and the collagen in between dissolved slowly. Figure 8. Boiled meat under the microscope (cross section). After some hours, fibers shrink inboiling water, as collagenic tissue gelatinize The theory also explains why it is true that meat has to be grilled very fast: reducing the cooking timereduces the water losses. As water content is linked with tenderness and jutosity (how much juice isreleased when meat is chewed), meat cooked for a short time is better than meat cooked on a slowfire for long.It should be also mentioned that diffusion of odorant and taste molecules into meat does not generallyoccurs during cooking: meat cooked for 20 hours in a solution of fluorescein (a fluorescent yellowpigment) is not colored at the core. Hence it is wrong to speak of "cooking by concentration", forroasting, as there is no concentration during this process: juice cannot come at the centre, becausethere is no empty space where it could go, and water (most of the meat) is cannot be compressed. Asa consequence, there can be any "concentration" of juice, as many culinary textbook indicate wrongly.Moreover, there cannot be any flavour concentration, as odorant and taste molecules cannot go at thecentre of the meat except by diffusion, which is a very slow process (in a gelatine gel with 1% gelatine,where diffusion is easier than in meat, because there is no collagenic tissue, diffusion takes place at aspeed of only 1 cm per day). In September 2004, the expression "cooking by concentration" wasdropped from the French culinary curriculum.The other expression, "cooking by expansion", was also dropped. This expression referred to boilingmeat, and it is strange that it survived for so long, as any cook can easily observe that meat isshrinking when boiled.Moreover experiments demonstrate how wrong this old theory is. It was written, even in recenttextbooks, that, when producing meat stock, meat should be put in cold water, "otherwise albumincoagulation at the surface, in boiling water, would prevent juices from going from the meat to thestock". True or not?First it should be emphasized that "albumin" is a very old (more than one century) word for what arenow called proteins. It is true that there are some albumins (serum albumin) in blood (and therefore inmeat), but meat cooking is not due to albumin coagulation: the proteins that coagulate are actin,myosin and others. An easy experiment can be done to check the culinary theory: if it were true thatmeat coagulation at the surface, in boiling water, prevents juices losses, then meat put in boiling watershould be heavier than meat in initially cold water. A balance is enough to check this.Let's divide a piece of meat into two equal parts, with the same amount of fat in both pieces, and let'scook one piece in boiling water, and the other one in initially cold water. Every ten minutes or so, let'stake the two pieces, dry them rapidly and weigh them. The following curve is obtained: Figure 9. The mass of two pieces of meat put either in initially cold or boiling temperaturevaries differently, but is equal after about two hours. Contrary to the theory saying that meatput in boiling water looses les "juices" than meat put in cold temperature, it is observed thatthe mass is lower in boiling water. This is due to shrinking of heated collagenic tissue: at thistissue is more heated in boiling water than in cold water, the mass of excluded liquids ishigher.According to the old culinary theory, the lower curve should refer to meat cooked in initially cold water,and the upper curve should correspond to meat put in boiling water... but the reverse is observed! Itcan be seen that meat shrinking in boiling water expels juices in the stock, and that, after about two hours, the two pieces have lost the same amount of matter. Clearly the old theory should beabandoned. Why this meat shrinking? Food science can tell that collagen is responsible for it, and that thisshrinking is partly reversible. This can be seen when the meat cools in its stock: Figure 10. When meat is cooked either in initially cold or boiling water, the mass is the sameafter about two hours, an did does not change later. However, if the temperature is reduced,the meat absorbs some of the cooking solution. When heated again, the mass is reduced to theformer equilibrium point... until collagenic tissue is dissolved and muscular fibres go apart.In this experiment, meat was cooked in either initially cold or boiling water for many hours. At time1000 minutes, heating was stopped, and meat was let to cool in the stock. It can be seen that themeat absorbed some stock during cooling. After this step, the meat and the stock were heated again,and the same lower mass than before was obtained. The conclusion of this experiment, than can berepeated as long as collagen is not entirely dissolved, is that meat is like a "thermal sponge".