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Questions and answers about spoiled meat

FAQ from November 29, 2005

Raw meat can spoil very easily. Correct storage is all the more important: it should always be refrigerated, temperatures below +7 ° C are best (it is best to keep a refrigerator temperature of 2-4 ° C). Then pathogenic germs that are on the surface of the meat can only multiply slowly. You can recognize spoiled meat by the fact that it changes its appearance, texture, smell and taste. It shouldn't be eaten anymore. Its consumption can cause severe food infections such as diarrhea. Rotten meat is a hygiene issue. The BfR has compiled and answered the most frequently asked questions below.

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Colloquially, spoilage means bacterial spoilage or putrefaction. However, bacteria are just one of several possible causes of spoiled food, albeit the most common. Corruption processes are generally considered to be a hygiene problem in the broader sense.

We speak of microbial spoilage when microorganisms such as bacteria or molds, through their reproduction and metabolic activity, change the composition of a food to such an extent that it is no longer suitable for consumption. How much and how quickly food spoils depends on whether various circumstances, such as the storage temperature, favor or limit the multiplication of the bacteria present.

In addition to bacterial spoilage, there are also biological and chemical-physical causes. The biological causes of meat spoilage are, for example, "boar odor" (strong smell) or the occurrence of parasites and pests. Biochemical causes of meat spoilage can manifest themselves, for example, in the form of a stifling maturation of the meat, if it takes on a brown-red color and smells sour to putrid and musty if the game or poultry is insufficiently cooled. Even if it dries out (freezer burn) or is contaminated with dust or even excrement particles, one speaks of spoiled.

The composition of the meat is of decisive importance as to whether microbial germs multiply in and on the meat: Basically, meat is easily perishable as the meat surface is only imperfectly protected against the ingress of bacteria and meat is a good breeding ground for bacterial growth. If, in addition, the protective covering of the muscle, such as. B. in minced meat or goulash, is destroyed, microorganisms can multiply without restriction. If the food is stored in a cool place (+2 - +7 ° C), it will spoil after two days at the latest. When not minced, the same meat can be kept much longer if stored in a cool place, up to two weeks.

Bacteria on meat, the so-called meat flora, multiply best in the range between +18 and +30 ° C. For this reason, meat should be chilled as quickly as possible after slaughtering to + 7 ° C and the by-products (such as liver or kidneys) from slaughtering to + 3 ° C.

If meat is not refrigerated at all or if the refrigeration has only been temporarily interrupted, there is an increased risk that pathogenic germs will multiply quickly in and on the meat.

The meat is attacked by germs during the slaughtering process. When slaughtering, the surfaces can become heavily soiled, which is primarily caused by fecal particles, for example from animal skin. It is therefore mainly intestinal bacteria that are the first to colonize the surface of fresh meat: enterobacteria, micrococci, fecal streptococci, pseudomonads, lactobacilli and aerobic spore formers.

Under perfectly hygienic conditions there are about 1,000 germs per cm on the surface of beef and about 10,000 germs per cm of pork2. The enterobacteria, among which there may also be individual pathogenic germs such as E. coli or salmonella, usually only make up a very small proportion, namely no more than 10 to 100 per cm2, out.

The fresh meat can be contaminated with a large number of different types of bacteria through external and internal influences. One of the most important factors for these bacteria to continue to multiply on meat is temperature. Constant cooling leads to a special bacterial flora. One speaks of the so-called "cold store flora", which can multiply even under cool conditions. Heat-loving types of germs recede more and more within a few days. A bacterial flora moves into the foreground, which makes up only a fraction of the total germ content on the meat surface immediately after slaughter. One observes bacteria that z. B. in connection with high moisture content such. B. splashed on the meat during slaughter, which can lead to deviations in smell and color of the meat.

Experience shows that the germ content of frozen meat decreases during storage. Bacterial spores, on the other hand, usually survive freezing temperatures without damage and can multiply again after the meat has been thawed.

Proper freezer storage is the gentlest method of preserving meat and meat products over the long term. The shelf life of frozen meat depends on the storage temperature and the type of meat. If the storage conditions are good (prevent drying out!) And a temperature of approx. B. for pork from a shelf life of 6-9 months and for beef of 9-18 months. The shelf life of frozen meat is limited in particular by the deterioration of fat (becoming rancid).

A high water content (also called water activity), a high storage temperature and a high pH value promote the spoilage of meat. After the meat has matured (this is the period in which the meat is tender at temperatures from -1 ° C to +2 ° C, including through enzymatic processes), pork usually has pH values ​​in the range of 5.6 to 6 , 2. From a pH value of 5.8 and below, the growth rate is delayed e.g. B. of enterobacteria and cold-loving bacteria noticeably.

Watery meat, which is also known by the technical term pale, soft and exudated (PSE) meat, is less durable due to its higher water content. Meat with so-called dark, firm and dry (DFD) properties also spoils more easily than "normal" meat, as it has pH values ​​that are closer to the optimum growth of germs that are responsible for meat spoilage. Hereditary factors in the animals and stress on the animals before slaughter are responsible for the PSE and DFD properties of the meat.

The oxygen tension (in the technical term redox potential) during storage, which, for example, develops differently in the absence of air and vacuum packaging than in open and cool storage, has an influence on the spectrum of bacteria and their growth properties.

The physico-chemical, biochemical or microbiological changes in a spoiled food usually lead to significant changes in appearance, consistency, smell and taste. The consumer can tell from these changes that meat has gone bad. Consumers should stop eating this meat. However, they do not always recognize spoiled meat.

Almost all foods on which pathogenic microorganisms can multiply are easily perishable. In addition to the development of spoilage flora, there may also be a multiplication of pathogenic bacteria that do not themselves cause any sensory signs of spoilage such as a changed appearance, changed consistency, changed smell or taste. The most important pathogens in this context are salmonella, staphylococci, EHEC (enterohaemorrhagic E. coli) To count bacilli and clostridia. They cause the classic symptoms of food poisoning, such as nausea, diarrhea, and vomiting. If meat spoils at cold store temperatures, enterobacteria can multiply on the surface of the meat. B. for salmonella. Clostridia can multiply in the depths of the muscles, and their toxins also lead to diarrhea and vomiting.