All you should know about meat
Kjell Ivar Hildrum
7. June 2010
Meat has always had a special place in our diet; for many of us it’s the main attraction in a good meal. We know when the meat is tender, but we don’t know enough about what makes meat tender or tough. Here’s a brief explanation.
Meat’s high status means that many people follow news items about meat closely. Nutrition experts tell us that we eat too much meat and anthropologists point out that we have an insatiable desire for blood and meat, while chefs cannot agree about the right way to cook a piece of meat. As a meat researcher, my contention is that everyone needs more basic knowledge about meat.
The most important qualities of a meat product are linked to hygiene, technology, nutrition and sensory properties (especially taste). Quality is very much governed by the meat’s composition, especially of the main components water, fat and protein. This applies to all kinds of meat. The meat’s physical condition and structure is also important to how the quality is perceived. Fat, water and protein make up as much as 97-98% of the weight of a piece of meat.
Fat, water and protein
For beef, the fat in a piece of raw meat can vary between 0 and 40%, water between 45% and 75% and protein between 14% and 22%. A very fat piece of meat might have 38% fat and 14% protein, but still 47% water. When producing meat products like sausages and meat patties, there is not enough protein to bind together the fat and water, or to satisfy the meat regulations. Protein must therefore be added.
A very lean piece of meat, for example, might contain just 3% fat, while the protein and water content in the same piece would be 22% and 76% respectively. If these variations are not under control when minced meat and sausages are being made, then there will be great variations in the quality of the end product. The amounts of fat, water and protein in a piece of meat are closely connected. This means that if we know the fat content, we can work out the amount of protein and water.
Healthy or unhealthy?
Meat is an important source of valuable nutrients that contribute to better health and to reducing the risk of cancer and other illnesses. The muscles of all kinds of animals are rich in the amino acids that must be included in a proper diet. Examples of other important substances in meat include vitamins A and B12 and folic acid, as well as minerals such as iron and selenium. Meat is rich in proteins, but low in sugars. That contributes to a low glycaemic index, which can help to reduce obesity, diabetes and cancer.
On the other hand, meat contains saturated and unfavourable fat, which can lead to obesity, heart disease and possibly cancer. It is important to stress that raw, lean meat is not in itself a risk factor for cancer. Earlier reports that high protein foods could cause cancer in mice have been largely disproved by new studies, but some methods of processing meat may be unfortunate. When meat is grilled or fried at high temperatures, mutagens and other substances that might be unfortunate for our health are created.
A diet with high fat content is not desirable, but the relationship between saturated and unsaturated fat in meat is important. As many people know, unsaturated fat is useful for our health and saturated fat is undesirable. High levels of saturated fat in the diet can raise cholesterol and increase the risk of heart disease. The pattern of fatty acids in meat varies in different kinds of animals. Beef and lamb have the least unsaturated fat, followed by pork, while poultry has the most unsaturated fat. We can see that in pork the fat nearest the skin is the most unsaturated, while in beef and lamb there is little difference.
It is often said that white meat from chicken is healthier than red meat like beef or lamb. This is correct as far as fat content in the meat is concerned. If the fat is cut away, there is little proof that red meat is any worse than white. Another point is that beef is heavier to digest and encourages a little rest after dinner.
Unsaturated fat has a lower melting point than saturated. Grinding and chopping pork and chicken must therefore be done at a lower temperature than for beef and lamb. Unsaturated fat also becomes rancid more easily, which means that pork and poultry have a shorter chemical shelf life (rancidity) than beef or lamb. This is especially important for frozen storage. The presence of oxygen or air strongly stimulates rancidity, so packaging for pork and poultry must be especially airtight and have little air left inside to achieve good chemical keeping properties.
Protein is the most important building block in meat; it determines structure and connectivity. The two main groups of proteins in meat are muscle protein and connective tissue. The muscle proteins are biochemically active and change significantly after slaughter and during aging, while the collagen is fairly stable. Collagen is the most important group of connective tissues. The content of collagen varies greatly between different muscles and is largely decisive in whether a particular muscle type can be tender or not. Tender muscles like fillet steak have little collagen, while brisket and chuck steak have considerably more. When meat is aged, the long fibres in the muscle protein are split and make the muscle easier to chew.
When a muscle loses energy and the pH value no longer falls, the pumps in the cell membranes that keep calcium away from the muscle fibres weaken. There then occurs a gradual muscle contraction in the meat called rigor mortis. After a certain time the maximum muscle contraction passes its peak. After this the meat starts to become more tender as the texture of the meat becomes looser. The more powerful the muscle contraction in the meat has been, the tougher the meat becomes afterwards and the longer it takes for the meat to become tender.
After slaughter, the carcass must be cooled rapidly for reasons of bacterial growth and keeping qualities. If the cooling is too rapid, there will still be energy in the meat when the temperature becomes low. The muscle uses this energy to contract powerfully and we get cold contraction. Aging this meat has little effect since bonds created are very strong and the result will be tough meat. Chilling the meat slowly can also cause too much contraction, and this heat contraction also results in tough meat. Since the muscles in a carcass will cool at different speeds, according to size, it is possible to get both heat and cold contraction in the same carcass. If the carcass is cut up before chilling (hot boning), the problem can be avoided.
There are great differences in the speeds with which different types of meat become tender during aging. Chicken becomes tender in such a short time that no special aging is necessary. If the chicken is tough, however, this may be due to the meat drying out or incorrect preparation. Pork normally requires a few days to arrive at the best degree of tenderness. Beef and lamb take the longest time and should be aged for at least a week, or even longer depending on which muscle in the carcass we are talking about. There are no great differences in tenderness between different breeds , quite the opposite of what is often claimed. The differences between the individual animals of a particular breed are usually much greater.