Low temperature preservation of food pdf

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Curing salt, also known as “Prague powder” or “pink salt”, is typically a combination of sodium chloride and sodium nitrite that is dyed pink to distinguish it from table salt. Nitrates and nitrites, in conjunction with salt, are the most common agents in curing meat, because they further inhibit the growth of Low temperature preservation of food pdf botulinum. They also contribute to the characteristic pink color.

Slices of beef in a can. Untreated meat decomposes rapidly if it is not preserved, at a speed that depends on several factors, including ambient humidity, temperature, and the presence of pathogens. Most meats cannot be kept at room temperature in excess of a few days without spoiling. If kept in excess of this time, meat begins to change colour and exude a foul odour, indicating the decomposition of the food. Ingestion of such spoiled meat can cause serious food poisonings, like botulism. While the short shelf life of fresh meat does not pose a significant problem when access to it is easy and supply is abundant, in times of scarcity and famine, or when the meat must be carried over long voyages, it spoils very quickly.

In such circumstances the usefulness of preserving foods containing nutritional value for transport and storage is obvious. Curing can significantly extend the life of meat before it spoils, by making it inhospitable to the growth of spoilage microbes. A survival technique since prehistory, the conservation of meat has become, over the centuries, a topic of political, economic, and social importance worldwide. Sur un fond noir se détache le profil ocre d’un jeune homme tenant de la main gauche le groin d’une tête de porc posée sur un tabouret, et de la droite un long couteau, haut levé et près à s’abattre sur la hure. Young man preparing a pig’s head after a sacrifice. Food curing dates back to ancient times, both in the form of smoked meat and salt-cured meat. Several sources describe the salting of meat in the ancient Mediterranean world.

Also evidence of ancient sausage production exists. Preserved meats were furthermore a part of religious traditions: resulting meat for offerings to the gods was salted before being given to priests, after which it could be picked up again by the offerer, or even sold in the butcher’s. A trade in salt meat occurred across ancient Europe. In Polybius’s time, the Gauls exported salt pork each year to Rome in large quantities, where it was sold in different cuts: rear cuts, middle cuts, hams, and sausages.

This meat, after having been salted with the greatest care, was sometime smoked. The smoking of meat was a traditional practice in North America, where Plains Indians hung their meat at the top of their tipis to increase the amount of smoke coming into contact with the food. In Europe, medieval cuisine made great use of meat and vegetables, and the guild of butchers was amongst the most powerful. During the 12th century, salt beef was consumed by all social classes. Smoked meat was called carbouclée in Romance tongues and bacon if it was pork.

In the 16th century, the most fashionable pâtés were of woodcock, au bec doré, chapon, beef tongue, cow feet, sheep feet, chicken, veal, and venison. Derrière une grille de métal, des barils sont couchés, empilés en trois étages et cette pyramide se termine par des tonneaux de bœuf salé. During the Age of Discovery, salt meat was one of the main foods for sailors on long voyages, for instance in the merchant marine or the navy. In the 18th century, salted Irish beef, transported in barrels, was considered finest.

Scientific research on meat by chemists and pharmacists led to the creation of a new, extremely practical product: meat extract, which could appear in different forms. In France, the summer of 1857 was so hot that most butchers refused to slaughter animals and charcutiers lost considerable amounts of meat, due to inadequate conservation methods. A member of the Academy of Medicine and his son issued a 34-page summary of works printed between 1663 and 1857, which proposed some solutions: not less than 91 texts exist, of which 64 edited for only the years between 1851 and 1857. The sugar added to meat for the purpose of curing it comes in many forms, including honey, corn syrup solids, and maple syrup. Nitrates and nitrites not only help kill bacteria, but also produce a characteristic flavor and give meat a pink or red color.

Nitrite salts are most often used in curing. The use of nitrite and nitrate salts for meat curing goes back to the Middle Ages, and in the US has been formally used since 1925. The use of nitrites in food preservation is controversial due to the potential for the formation of nitrosamines when nitrites are present in high concentrations and the product is cooked at high temperatures. The effect is seen for red or processed meat, but not for white meat or fish. Meat can also be preserved by “smoking”, which means exposing it to smoke from burning or smoldering plant materials, usually wood. If the smoke is hot enough to slow-cook the meat, it will also keep it tender. Smoking helps seal the outer layer of the food being cured, making it more difficult for bacteria to enter.

It can be done in combination with other curing methods such as salting. Smoke roasting and hot smoking cook the meat while cold smoking does not. The smoking of food directly with wood smoke is known to contaminate the food with carcinogenic polycyclic aromatic hydrocarbons. In 2015, the International Agency for Research on Cancer of the World Health Organization classified processed meat, that is, meat that has undergone salting, curing, fermenting, and smoking, as “carcinogenic to humans”. The improvement of methods of meat preservation, and of the means of transport of preserved products, has notably permitted the separation of areas of production and areas of consumption, which can now be distant without it posing a problem, permitting the exportation of meats.