On deciding to cook an “asado” we carefully consider everything that must be prepared previously so that nothing important is missing.
We choose the best wood and charcoal for the fire, select the meat, the seasoning, utensils and knives. One must always have a couple of old newspapers to start the fire and clean the grill, which is sure to be dirty after the last “asado”.
First we prepare the “pyre” with the chosen materials needed for the fire. Underneath it all we put some screwed up pieces of newspaper, on top of that a few bits of cardboard to hold the dry twigs stolen from a dead tree in the neighbour’s garden, then a pyramid of logs; in the gaps some chosen chunks of charcoal. It is important that air circulate between all these layers so that the fire does not go out.
Our aim is to make a little “asado” so that our guests leave with a full stomach and a contented smile on their faces, however, what we are unaware of, is that from the moment we start cooking, we are inviting them to participate in some amazing physical and chemical phenomena.
OXIDATION GIVES LIFE TO OUR FIRE
Observe an old bicycle leaning against a tree, it is covered in rust but the tree isn’t. This is because combustible material does not rust quickly; we never see rusty paper or wood. The air we breathe is 21% oxygen, which permits life to exist, to rust the bicycle and for us to be successful cooks of a tasty “asado”.
Everything placed on the “pyre” is highly flammable, but they won’t burn as they stand, if, however, the temperature is increased we can accelerate the oxidation making them react with the surrounding oxygen. This chemical reaction is called COMBUSTION and when it reaches a certain temperature it produces flames and releases energy in the form of heat. In order to set this in motion all that is needed is a lit match that will start a chain reaction when we touch it to the paper. This will then set the cardboard on fire, which will light the stolen twigs, and these in turn will set fire to the logs and coal… That’s it! We have a lovely little fire full of combustion.
TRANSFERRING THE HEAT
When the coals are ready, little by little we carefully put them under the grill. We choose the thickest cuts to place on the grill first leaving the thinner ones for later.
As soon as the first piece of meat is placed on the grill, without our even realising it, a series of phenomena related to the transference of energy are set in motion. These phenomena are studied by Thermodynamics, which has its own laws.
Just so as to give you an idea of what this is about, let me tell you that our mothers applied law 0 (zero) of thermodynamics (Ref 26). When we complained that the milk was too hot we were told that in order to cool it down we should put a teaspoon in the cup or another solution was to pour the hot liquid into another cold cup. This law basically says that when we put two objects in contact with each other at some point they will all reach the same temperature.
Back to our grill and the beautiful red coals spread under our choice cut. We keep an eye on it while drinking a glass of good red wine and accompanied by some mature cheese. While thus occupied, various physical phenomena and mechanisms related to the transference of heat that will cook our “asado”, are taking place. These are:
THERMAL CONDUCTION: The hot irons of the grill conduct the heat onto the meat through contact. The outer surface of the meat transmits heat into the interior that is colder and thus the cut cooks. It is due to the difference between the temperature of the iron and the meat that the latter has the typical toasted grill pattern.
CONVECTION: The air is heated by the hot coals and rises generating a continuous current due to the entry of cold air at the base of the grill. This hot air envelops the meat, cooking it whilst rising up and out through the chimney. A common “trick” when cooking outdoors is to cover the meat with a piece of cardboard in order to best use this enveloping heat.
RADIATION: The hot coals radiate energy in the form of heat that is transmitted in the form of electromagnetic waves onto the grill and the meat. This is difficult to understand, it seems as if our “asado” is being electrocuted, but the waves exist and do not need a physical means to transmit the heat. This is easily shown when drawing a grill with the coals beneath. How do you draw the heat that the coals radiate? See? With waves, lots of waves. The sun produces a similar effect on our planet but with waves of different length.
Amazing isn’t it? All this is happening while we hold a long fork in one hand and a glass of wine in the other.
These phenomena and laws of physics (there are many more) explain much of what is going on when we are cooking, be it on a grill or in the kitchen. But, as you can see, we grill experts are in fact managing many more physical phenomena than those who cook on a griddle or in an oven. So from now on we will accept the respectful title of “Doctor” or “Sir”
In the second part of this treatise we will talk of PHYSICS AND CHEMISTRY OF MEAT
BUT JUST REMEMBER ONE THING
THERE IS NO LAW WHICH GOVERNS THE LOVE OF COOKING OR THE GRILL ITS SOURCE IS THE NEED TO BE HAPPY AND TO MAKE OTHERS HAPPY
(26) It is called Law 0 because it was postulated after numbers 1 and 2, but as it was considered fundamental it was placed before the others. Any moment physicists will discover Law 1.5!!