Post 3 of a series of digests from the magisterial ‘On food and cooking’ by Harold McGee. I may augment these posts as I come across nuggets of information from other sources.
Meats’ nutritional composition varies considerably. Pork is on average 12% protein and 45% fat while chicken is 30% and 5% respectfully. With regard to fat, the fat component of beef varies considerably with the cut and grade of animal. With pork and lamb the fat content is more consistent (and higher) so there is less differential with ‘lean’ meat.
Meat has three primary components – muscle fibre, connective tissue and fat. As a rule meat will be tough when the muscle fibres are coarse rather than fine, when there is a lot of connective tissue and when the meat is lean (low in fat).
Young animals have smaller diameter muscle fibres that have been little used. As the animal ages the fibres enlarge, with the muscles least used enlarging the least. This is why beef fillet is tenderer than shoulder, which is in constant use.
Fat contributes to tenderness in cooking by penetrating the muscle tissue and helping separate fibre from fibre.
Muscle fibres divide into ‘slow-twitch’ that burn fat with oxygen and are generally darker and ‘fast-twitch’ that burn the carbohydrate glycogen without oxygen, producing lactic acid as a by-product, and are whiter. The slow fibres characterise muscles in constant use and are more flavoursome.
Animals slaughtered when under stress produce meat that is less acidic and of lower quality. Carcasses are then hung, for two reasons: they are bled to reduce the risk of spoilage and hanging extends the muscles to help relax them from rigor mortis, which occurs in the days following slaughter.
Beef is improved by aging for 10 days to several weeks, lamb for up to a week. In aging it appears that lactic acid breaks down the cell walls liberating enzymes that attack the meat proteins. This liberates amino acids that cause flavour changes. And the meat becomes more tender. However the connective tissue is not much effected. The meat loses water by evaporation, intensifying flavour.
An inevitable consequence of cooking meat is the loss of some juice, more pronounced with longer or hotter cooking. B vitamins are carried away by the juices. Cooking meat creates the characteristic flavour in two ways. First the cell membrances are damaged allowing cell contents to mix and undergo chemical changes. A significant element here are fats, which are transformed to receptacles of flavour. This explains why lean meat can be a disappointment in the mouth. Second, intense heat favors the Maillard reactions, exceedingly complex chemical reactions mostly involving proteins and carbohydrates. It is easiest to obtain high temperatures on the surface of the meat so browning reactions concentrate in a crust where the meat is roasted, grilled or fried. Keep the surface of the meat dry to maximise Maillard. For example salt and refrigerate the day before, then take out, pat dry and allow to come to room temperature.
The most straightforward way is cutting, pounding or grinding the meat to break down the structure of the muscle bundles. Cutting and pounding are only useful for fairly thin cuts and grinding produces a new substance entirely.
Chemical tenderisers may be used. The enzyme papain found in papaya leaves and fruit, and enzymes in figs, pineapple and some fungi will digest proteins. However this only effects the surface of the meat and will also cause fluid loss, therefore drier meat, and the enzymes do not accomplish much below 60°C, and they are inactivated at boiling point. Foods with digestive enzymes will of course introduce these to the digestive tract, where they may directly aid in digestion of the masticated meat.
Acid marinades like wine, vinegar or citrus tenderise the surface of meat, again with drier meat the result.
The muscle fibres shrink and shorten with heat, reaching their limit at about 77°C. Their proteins uncoil and coagulate. This causes the meat to look more and more opaque and to exude juice as the coagulating proteins squeeze out fluids. By 77°C the meat is well-done, smaller, denser and less moist.
On the other hand the collagen in connective tissue requires more intensive cooking to be converted into soft gelatin, which begins at 60°C but is more rapid approaching 100°C.
Cooking tender meat therefore requires compromise.
A fallacy: that ‘searing’ the outside of meat seals in the meat juices and nutrients. In fact a seared crust does nothing to inhibit moisture loss; its main benefit is the creation of ‘browning reaction’ flavors, and as such can be done at the beginning or the end of cooking.
Fish and shellfish have short muscle fibres, fragile connective tissue and little fat so must be cooked quite differently to other meats. As little as possible, only to the point that the muscle proteins coagulate.
Organ meats such as liver and kidneys contain little connective tissue so must be treated gently and cooked briefly. Hearts and other muscular variety meats on the other hand are lean well-exercised meat and require long slow cooking.
Grilling occurs with element temperatures in excess of 1000°C and is suited to thin tender cuts like chops and steaks. Connective tissue does not have the time to be broken down but the intense temperature produces strong browning reaction flavours.
Pan frying is limited to the smoking point of fat used – unclarified butter 121°C, vegetable oils 232°C. The meat surface is browned quickly in a minute or two and the heat is usually reduced to prevent the surface being toughened. If the pan is covered a process more like braising results.
Roasting relies on infrared radiation and convective heat transfer so is relatively slow and suited to large pieces of meat. If your main concern is juiciness do not bother to sear the meat. A relatively high temperature and shorter cooker time works well for cuts with little connective tissue, such as rib roast. Low temperature and prolonged cooking will be better for less tender cuts, like rump. Pork and lamb, coming from younger animals and with more fat, are less effected by changes in cooking temperature. Take the roast out when 5° below the desired temperature and it will continue cooking. Carve with a very sharp knife to cut through the tissues cleanly and minimise juice loss.
Braising, for example the pot roast, will bring the meat close to boiling temperature right through fairly quickly. Cuts with a lot of connective tissue respond well to braising but premium cuts will be made tougher. Small tender cuts like chops can be braised just to the point of done-ness. It is advisable to sear the meat before braising.
Internal meat temperatures ‘C
Beef / chicken / pork : 63 rare / 71 medium / 77 well-done.
Chicken : 63 just done / 68 done.