Curing (food preservation)
Curing is any of various food preservation and flavoring processes of foods such as meat, fish and vegetables, by the addition of a combination of salt, nitrates, nitrite or sugar. Many curing processes also involve smoking, spicing, or cooking. Dehydration was the earliest form of food curing. Salting or curing draws moisture from the meat through a process of osmosis. Meat is cured with salt or sugar, or a combination of the two. Nitrates and nitrites are also often used to cure meat and contribute the characteristic pink color, as well as inhibition of Clostridium botulinum. Curing was the primary way of preserving meat and fish until the late 19th century.
Necessity of curing
Meat degrades if it is not preserved, at a speed that depends on several factors: its acidity, the ambient humidity, the presence of pathogens, and the temperature.
In 1836, the food safety officer Burnet gave the times that different meats will keep in temperate climates, given that they are hung individually in the air without touching metal, stone, or wood, and specifying that they fare better if kept away from heat, water, and air:
|Animal||In summer||In winter|
|Roe deer, Red deer||4||8|
|Hare, capon, old landfowl||3||6|
|Veal, lamb, chicken, pigeon||2||4|
Beyond these times, the meat changes colour and begins to exude a foul odor which ought to alert the cook that the ingestion of the spoiled meat could cause serious food poisoning.
Even if one plans to use the meat before it spoils, curing can facilitate storing and transport, or constitute a first step in a recipe.
The keeping times for raw meat cited in the table above pose few problems during times of nutritive abundance or for those who have the financial means of procuring fresh meat. In times of scarcity or famine, or during voyages over land or sea, it is harder to keep raw meat fresh, which drove humanity early in its history to find a means of conserving this food of great nutritional value, obtained by hunting or husbandry. A survival technique since prehistory, the conservation of meat has become over the centuries a topic of political, economic, and social importance worldwide.
Several sources describe the salting of meat in the ancient Mediterranean world. Diodore of Sicily in his Bibliotheca historica wrote that the Cosséens in the mountains of Persia salted the flesh of carnivorous animals. Strabo indicates that people at Borsippa were catching bats and salting them to eat. The ancient Greeks prepared tarichos (τάριχος), which was meat and fish conserved by salt or other means.[a] The Romans called this dish salsamentum – which term later included salted fat, the sauces and spices used for its preparation. There is also evidence of ancient sausage production. The Roman gourmet Apicius speaks of a sausage making technique involving œnogaros (a mixture of the fermented fish sauce garum with oil or wine). Preserved meats were furthermore a part of religious traditions: the extra meat used 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.
There is evidence of a trade in salt meat 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. These goods had to have been considerably important, since they fed part of the Roman people and the armies. The Belgians were celebrated above all for the care which they gave to the fattening of their pigs. Their herds of sheep and pigs were so many, that they could provide skins and salt meat not only for Rome, but also for most of Italy. The Ceretani of the Iberian peninsula drew a large export income from their hams, which were so succulent, that they that they were in no way inferior to those of Cantabria. These tarichos of pig would become especially sought, to the point that the ancients considered this meat the most nourishing of all and the easiest to digest.
In Ethiopia, according to Pliny, and in Libya according to Saint Jerome, the Acridophages (literally, the locust-eaters) salted and smoked the crickets which arrived at their settlements in the spring in great swarms and which constituted, it was said, their sole food.
The Middle Ages
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[f]
The Middle Ages made pâté a masterpiece: that which is, in the 21st century, merely spiced minced meat (or fish), baked in a terrine and eaten cold, was at that time composed of a dough envelope stuffed with varied meats and superbly decorated for ceremonial feasts. The first French recipe, written in verse by Gace de La Bigne, mentions in the same pâté three great partridges, six fat quail, and a dozen larks. Le Ménagier de Paris mentions pâtés of fish, game, young rabbit, fresh venison, beef, pigeons, mutton, veal, and pork, and even pâtés of lark, turtledove, cow, baby bird, goose, and hen. Bartolomeo Sacchi, called Platine, prefect of the Vatican Library, gives the recipe for a pâté of wild beasts: the flesh, after being boiled with salt and vinegar, was larded and placed inside an envelope of spiced fat, with a mélange of pepper, cinnamon and pounded lard; one studded the fat with cloves until it was entirely covered, then placed it inside a pâte.
In the 16th century, the most fashionable pâtés were of woodcock, au bec doré, chapon, beef tongue, cow feet, sheep feet, chicken, teal, and venison. In the same era, Pierre Belon notes that the inhabitants of Crete and Chios lightly salted then oven-dried entire hares, sheep, and roe deer cut into pieces, and that in Turkey cows and sheep, cut and minced rouelles, salted then dried, were eaten on voyages with onions and no other preparation.
Early modern era
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. The need to properly feed soldiers during long campaigns outside the country, such as the Napoleonic Wars, and to nourish a constantly growing population often living in appalling conditions drove scientific research, but it was a humble confectioner, Nicolas Appert, who in 1795 developed through experimentation a method which would become universal and in one language bear his name: airtight storage, called appertisation in French.
With the spread of appertisation, the 19th century world entered the era of the "food industry", which developed new products such as canned salt meat (for example corned beef), but also led to lowered standards of food quality and hygiene – such as those Upton Sinclair described in The Jungle. These bad practices led to the creation of the Pure Food and Drug Act in 1906, followed by the national agencies for health security and the establishment of food traceability over the course of the 20th century. It also led to continuing technological innovation. It was discovered in the 1800s that salt mixed with nitrates (saltpeter) would color meats red, rather than grey; consumers at that time then strongly preferred red-colored meat.
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 à 1857.
Table salt (sodium chloride) is the primary ingredient used in meat curing. Removal of water and addition of salt to meat creates a solute-rich environment where osmotic pressure draws water out of microorganisms, slowing down their growth. Doing this requires a concentration of salt of nearly 20%. In addition, salt causes the soluble meat proteins to come to the surface of the meat particles within sausages. These proteins coagulate when the sausage is heated, helping to hold the sausage together. Finally, salt slows the oxidation process, effectively preventing the meat from going rancid.
The sugar added to meat for the purpose of curing it comes in many forms, including honey, corn syrup solids, and maple syrup. However, with the exception of bacon, it does not contribute much to the flavor, but it does alleviate the harsh flavor of the salt. Sugar also contributes to the growth of beneficial bacteria like Lactobacillus by feeding them.
Nitrates and nitrites
Nitrates and nitrites not only help kill bacteria, but also produce a characteristic flavor and give meat a pink or red color. Nitrite (NO2−), generally supplied by sodium nitrite or (indirectly) by potassium nitrate, is used as a source for nitrite (NO2−). Nitrite salts are most often used in curing. Nitrate is specifically used only in a few curing conditions and products where nitrite (which may be generated from nitrate) must be generated in the product over long periods of time.
Nitrite further breaks down in the meat into nitric oxide (NO), which then binds to the iron atom in the center of myoglobin's heme group, reducing oxidation and causing a reddish-brown color (nitrosomyoglobin) when raw, and the characteristic cooked-ham pink color (nitrosohemochrome or nitrosyl-heme) when cooked. The addition of ascorbate to cured meat reduces formation of nitrosamines (see below), but increases the nitrosylation of iron.
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. Because of the relatively high toxicity of nitrite (the lethal dose in humans is about 22 milligrams per kilogram of body weight), the maximum allowed nitrite concentration in meat products is 200 ppm. At these levels, some 80 to 90% of the nitrite in the average U.S. diet is not from cured meat products, but from natural nitrite production from vegetable nitrate intake.
The use of nitrates in food preservation is controversial. This is due to the potential for the formation of nitrosamines when nitrates 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. The production of carcinogenic nitrosamines can be potently inhibited by the use of the antioxidants Vitamin C and the alpha-tocopherol form of Vitamin E during curing. Under simulated gastric conditions, nitrosothiols rather than nitrosamines are the main nitroso species being formed. The usage of either compound is therefore regulated; for example, in the United States, the concentration of nitrates and nitrites is generally limited to 200 ppm or lower. They are considered irreplaceable in the prevention of botulinum poisoning from consumption of cured dry sausages by preventing spore germination.
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. One method of smoking calls for a smokehouse with damp wood chips or sawdust. In North America, hardwoods such as hickory, mesquite and maple are commonly used for smoking, as are the wood from fruit trees such as apple, cherry, and plum, and even corncobs.
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. Common smoking styles include hot smoking, smoke roasting (pit barbecuing) and cold smoking. Smoke roasting and hot smoking cook the meat while cold smoking does not. If the meat is cold smoked, it should be dried quickly to limit bacterial growth during the critical period where the meat is not yet dry. This can be achieved, as with jerky, by slicing the meat thinly.
Impact of conservation
Since the 20th century, with respect to the relationship between diet and human disease (e.g. cardiovascular, etc.), scientists have conducted studies on the effects of lipolysis on vacuum-packed or frozen meat. In particular, by analyzing entrecôtes of frozen beef during 270 days at −20 °C (−4 °F), scientists found an important phospholipase that accompanies the loss of some unsaturated fat n-3 and n-6, which are already low in the flesh of ruminants.
The improvement of methods of meat conservation, 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.
For example, the appearance in the 1980s of conservation techniques under controlled atmosphere sparked a small revolution in the world's market for sheep meat: the lamb of New Zealand, one of the world's largest exporters of lamb, could henceforth be sold as fresh meat, since it could be preserved from 12 to 16 weeks, which would be a sufficient duration for it to reach Europe by boat. Before, meat from New Zealand was frozen and thus had a much lower value on European shelves. With the arrival of the new "chilled" meats, New Zealand could compete even more strongly with local producers of fresh meat. The use of controlled atmosphere to avoid the depreciation which affects frozen meat is equally useful in other meat markets, such as that for pork, which now also enjoys an international trade.
- In time the original term came to mean salted fish only, whereas salted meat was called kreas tarichrou (κρέας ταριχηρὸν), according to Athenaeus of Naucratis in his Deipnosophistae, IV, 14.137f (en ligne)
- Une boucherie avec auvent et, à front de rue, poutre avec crocs auxquels pendent deux jambons, au XIVe siècle : trois clients, sur la droite, masquent partiellement l’étal qui déborde de l'appuie-fenêtre vers la rue où il repose sur deux pilastres ; à l'intérieur de la boutique, le commerçant évalue le poids d’un gros morceau de viande placé sur le plateau d'une balance avec des poids posés sur l'autre ; à gauche, dans la rue, un homme va égorger un mouton.
- Intérieur d’une boucherie au XIVe siècle : au fond, un cochon est suspendu par les pattes arrière à des crocs près de deux jambons et d'une grande barde ; le boucher, placé derrière une large table carrée, tient haut levé le hachoir avec lequel il va débiter un morceau de carcasse en côtelettes ; à gauche, devant la table, un homme semble lui passer commande ; au centre de l'image et à l’avant-plan, une femme agenouillée tient de la main gauche un seau et tend un pot de la droite vers le cou d’un cochon couché sur le flanc et qu’un autre boucher va égorger ; à l’arrière-plan droit, un tonneau de bois semble être empli de sang
- Une boucherie avec auvent et, à front de rue, poutre avec crocs auxquels pendent des viandes, au XIVe siècle : derrière l’étal qui déborde de l’appuie-fenêtre vers la rue où il repose sur deux pilastres et sur lequel sont posés un pied de bœuf, des morceaux de côtes et un grand tranchoir, un boucher parle à celui va assommer à la masse un bœuf couché dans la rue devant la boutique, tandis qu’un enfant regarde la scène depuis la porte entrouverte
- Scène de chasse au XIVe siècle : sur la pente d'une colline, un sanglier encadré de quatre chiens jappant est tué à l’épieu par un chasseur ; à l’avant plan, un autre chasseur suit son chien qui poursuit deux lièvres
- Smoked pork lard still carries this name in English-speaking countries
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- Burnet, Dictionnaire de cuisine et d’économie ménagère. À l’usage des Maîtres et Maîtresses de maison, Fermiers, Maîtres-d’hôtel, Chefs de cuisine, Chefs d’office, Restaurateurs, Pâtissiers, Marchands de comestibles, Confiseurs, Distillateurs, etc., Librairie usuelle, Paris, 1836, 788 pages + 11 planches, p. 760.
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- A nomadic shepherd people, considered by classical authors to be made up of warriors et de brigands, was the object of a victorious campaign by Alexander the Great in the 4th century. Cf. Pierre Briant, État et pasteurs au Moyen-Orient ancien, Cambridge and Paris, 1982 (compte rendu).
- Diodore de Sicile, Bibliothèque historique, XIX, 19 cité par Koehler, 1832, p. 432, note 724 (p. 486).
- Strabon, Géographie, XVI, 1.7.
- (French) M. Koehler, Tarichos ou recherches sur l’histoire et les antiquités des pêcheries de la Russie méridionale, in Mémoires de l’Académie impériale des sciences de Saint-Pétersbourg, 6th series, book I, Imp. of the Académie impériale des sciences, Saint Petersburg, 1832, p. 347 à 490 (en ligne).
- (Latin) Apicii Coelii, De opsoniis et condimentis, sive arte coquinaria, libri decem. Cum annotationibus Martini Lister, Londres, 1705, livre II, ch. 2, p. 59.
- Cf. Joaquim Marquardt, La Vie privée des romains, 2, dans Manuel des antiquités romaines, 15, sous la dir. de Theodor Mommsen, Paris, 1893 [1874-1875], p. 52-56 et part. p. 54 (en ligne).
- Pliny, Histoire naturelle, VI, 35.17
- En Normandie par example : Léopold Delisle, Études historiques et archéologiques en province depuis 1848 cité dans la Revue des deux mondes, XI (XXIe année), Paris, 1851, p. 1048.
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- Pierre Belon, Voyage au Levant, les observations de Pierre Belon du Mans, de plusieurs singularités et choses mémorables, trouvées en Grèce, Turquie, Judée, Égypte, Arabie et autres pays estranges, 1553.
- Daniel Gilles et Guy Pessiot, Voiles en Seine 99. L’armada du siècle, Ptc, 1999, ISBN 2906258547, p. 110.
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- This article was partially translated from the French Wikipedia.
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- Article in The Scientist, Volume 13, No. 6:1, Mar. 15, 1999 (registration required).
- Post on April 29, 2012 "Making Cured Meats"