A roast is what the Gauls of Asterix do every time an adventure ends: they put a wild boar on the fire … and they roast it. The asados owe their success to two reasons. On the one hand, the surface of the meat, heated in the presence of oil or butter, hardens because its juice evaporates and the meat proteins coagulate; on the other, the components of the meat react chemically, originating aromatic and colored molecules. While that characteristic tasty crust forms, inside the collagen molecules, which make the meat stiff, degrade and, consequently, the meat becomes tender . If it is heated over a high heat for a short time, the juice from the inside does not diffuse too much to the outside and the meat retains its succulence. This is the reason why the oven door should not be opened : the steam released escapes, is replaced by part of the meat juice and, consequently, the roast dries out.
That is why the main problem with roasts is calculating the cooking time. To be perfect, it must reach a temperature of 70 degrees in the innermost part, essential to degrade collagen and soften muscles. How to know if it has been achieved without having to put a thermometer inside, for example, a turkey? Applying the so-called Fick relationship , which says that the time required for the center of a turkey to reach a given temperature is proportional to the square of its radius .
One of the main problems in baking is calculating the cooking time
And the braised? When we put, for example, a piece of meat in a closed container with a little liquid waiting for it to be absorbed, we are braising . In this case, the cooking process -which always consists of flavoring and softening- is carried out, first, over high heat, browning the surface and creating aromas and, secondly, softening over low heat . Now, how does the juice get into the meat? Why does it not come out of it, as it happens in the roast? By the same principle that makes water rise inside a chalk: osmosis. From the Greek to push , it plays a vital role in the survival of living cells and in different physiological processes. Thus, thanks to osmosis, with which the cell wall regulates the passage of nutrients into the cell , the rice immersed in water swells and the water rises inside the tree trunks. In braising, the liquid that we have put in the bottom is a highly concentrated juice, more than that existing inside the meat. Then the aromatic molecules of the carrots, onions, leeks, celery … pass into the meat : osmosis favors, through the cell membrane, the passage of those components in which the concentrations are different and verifying the areas of higher concentration to those of lower concentration.
