Curing (food preservation)

Curingis any of variousfood preservationandflavoringprocesses of foods such asmeat,fishandvegetables, by the addition ofsalt, with the aim of drawing moisture out of the food by the process ofosmosis. Because curing increases thesolute concentrationin the food and hence decreases itswater potential, the food becomes inhospitable for themicrobegrowth that causesfood spoilage. Curing can be traced back toantiquity, and was the primary method of preserving meat and fish until the late 19th century.Dehydrationwas the earliest form of food curing.Many curing processes also involvesmoking,spicing,cooking, or the addition of combinations ofsugar,nitrate, andnitrite.
Meat preservationin general (of meat fromlivestock,game, andpoultry) comprises the set of all treatment processes for preserving the properties, taste, texture, and color of raw, partially cooked, or cooked meats while keeping them edible and safe to consume. Curing has been the dominant method of meat preservation for thousands of years, although modern developments likerefrigerationand syntheticpreservativeshave begun to complement and supplant it.
While meat-preservation processes like curing were mainly developed in order to preventdiseaseand to increasefood security, the advent of modern preservation methods mean that in mostdeveloped countriestoday, curing is instead mainly practiced for its cultural value and desirable impact on the texture and taste of food. Forless-developed countries, curing remains a key process in the production, transport and availability of meat.
Some traditional cured meat (such as authenticParma hamand some authentic Spanishchorizoand Italiansalami) is cured with salt alone.Today,potassium nitrate(KNO3) andsodium nitrite(NaNO2) (in conjunction with salt) are the most common agents in curing meat, because they bond to themyoglobinand act as a substitute foroxygen,thus turning myoglobin red.More recent evidence shows that these chemicals also inhibit the growth of the bacteria that cause the diseasebotulism.
The combination of table salt with nitrates or nitrites, calledcuring salt, is often dyed pink to distinguish it from table salt.Neither table salt nor any of the nitrites or nitrates commonly used in curing (e.g.,sodium nitrate[NaNO3],sodium nitrite,and potassium nitrate) is naturally pink.
Meatdecomposesrapidly if it is not preserved. The speed of decomposition depends on several factors, including ambienthumidity, temperature, and the presence ofpathogens. Most types of untreated meat cannot be kept at room temperature for lengthy periods before spoiling.
Spoiled meat changes color and exudes a foul odor. Ingestion can cause seriousfood poisoning. Salt-curing processes were developed in antiquityin order to ensure food safety without relying on then unknown anti-bacterial agents.
The short shelf life of fresh meat does not pose significant problems when access to it is easy and supply is abundant. But in times of scarcity and famine, or when the meat must be transported over long distances, food preservation is necessary.
Curing significantly increases the length of time meat remains edible, by making it inhospitable to the growth of microbes.
Salt (sodium chloride) is the primary ingredient used in meat curing.Removal of water and addition of salt to meat creates asolute-rich environment whereosmotic pressuredraws water out of microorganisms, slowing down their growth.Doing this requires a concentration of salt of nearly 20%.
In sausage production, salt causes the soluble proteins to come to the surface of the meat that was used to make the sausages.  Theseproteinscoagulate when the sausage is heated, helping to hold the sausage together.
Thesugaradded to meat for the purpose of curing it comes in many forms, includinghoney,corn syrupsolids, andmaple 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 such asLactobacillusby feeding them.
Nitrates and nitrites extend shelf life,help kill bacteria, produce a characteristic flavor and give meat a pink or red color.Nitrite (NO2) is generally supplied bysodium nitriteor (indirectly) bypotassium nitrate. Nitrite salts are most often used to accelerate curing and impart a pink colour.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 intonitric oxide(NO), which then binds to the iron atom in the center ofmyoglobin'shemegroup, 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 ofnitrosamines(see below), but increases thenitrosylationof iron.
The use of nitrite and nitrate salts for meat 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 mg/kg of body weight), the maximum allowed nitrite concentration in US meat products is 200ppm. Plasma nitrite is reduced in persons withendothelial dysfunction.
Nitrite-containingprocessed meatis associated with increased risk of developing colorectal cancer.Adding nitrites to meat has been shown to generate known carcinogens such as nitrosamines,N-nitrosamidesand nitrosyl-heme, resulting fromnitrosylationreactions; theWorld Health Organization (WHO)advises that each 50 g (1.8 oz) of "processed meats" eaten a day would raise the risk of getting bowel cancer by 18% over a lifetime; "processed meat" refers to meat that has been transformed through salting, curing, fermentation, smoking, or other processes to enhance flavour or improve preservation. The World Health Organization's review of more than 400 studies concluded, in 2015, that there was sufficient evidence that "processed meats" caused cancer, particularly colon cancer; the WHO'sInternational Agency for Research on Cancerclassified "processed meats" as carcinogenic to humans (Group 1).
The use of nitrites in food preservation is highly controversialdue to the potential for the formation ofnitroso-compounds such as nitrosamines,N-nitrosamidesand nitrosyl-heme.When the meat is cooked at high temperatures, nitrite-cured meat products can also lead to the formation of nitrosamines.The effect is seen for red processed meat, but not for white meat or fish.Nitrates and nitrites may cause cancer and the production of carcinogenic nitrosamines can be potently inhibited by the use of the antioxidantsvitamin Cand thealpha-tocopherolform ofvitamin Eduring curing.Under simulated gastric conditions,nitrosothiolsrather than nitrosamines are the main nitroso species being formed.The use 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.
Themeat industryconsiders nitrites irreplaceable because they speed up curing and improve color while retarding the growth ofClostridium botulinum,the bacteria that causesbotulism. Botulism, however, is an extremely rare disease (less than 1000 cases per year reported worldwide) and is almost always associated with home preparations of preserved food.For example, allParma hamhas been made without nitrites since 1993, but was reported in 2018 to have caused no cases of botulism.
Furthermore, while theFDAhas set a limit of 200 ppm of nitrates for cured meat, they are not allowed and not recognized as safe by the FDA in most other foods, even foods that are not cooked at high temperatures, such as cheese.
Processed meats without "added nitrites" may be misleading as they may be using naturally occurring nitrites from celery instead.
A 2019 report fromConsumer Reportsfound that usingcelery(or other natural sources) as a curing agent introduced naturally occurring nitrates and nitrites. The USDA allows the term "uncured" or "no nitrates or nitrites added" on products using these natural sources of nitrites, which provides the consumer a false sense of making a healthier choice.
TheConsumer Reportsinvestigation also provides the average level of sodium, nitrates and nitrites found per gram of meat in their report.
Consumer Reportsand the Center for Science in the Public Interest filed a formal request to the USDA to change the labeling requirements in 2019.
Meat can also be preserved by "smoking". If the smoke is hot enough to slow-cook the meat, this will also keep it tender.One method of smoking calls for asmokehousewith damp wood chips orsawdust.InNorth America,hardwoodssuch ashickory,mesquite, andmapleare commonly used for smoking, as are the wood from fruit trees such asapple,cherry, andplum, and evencorncobs.
Smoking helps seal the outer layer of the food being cured, making it more difficult forbacteriato 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 withjerky, by slicing the meat thinly.
The smoking of food directly with wood smoke is known to contaminate the food with carcinogenicpolycyclic aromatic hydrocarbons.
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 oflipolysison vacuum-packed or frozen meat. In particular, by analyzingentrecôtesof frozen beef during 270 days at −20 °C (−4 °F), scientists found an importantphospholipasethat accompanies the loss of someunsaturated fatn-3 and n-6, which are already low in the flesh ofruminants.
Elevated levels ofnitritesin preserved meats increase the risk ofnasopharyngeal cancer.
In 2015, theInternational Agency for Research on Cancerof theWorld Health Organizationclassified processed meat, that is, meat that has undergone salting, curing,fermenting, or smoking, as "carcinogenicto humans".
A survival technique sinceprehistory, the preservation of meat has become, over the centuries, a topic of political, economic, and social importance worldwide.
Food curing dates back to ancient times, both in the form ofsmoked meatandsalt-cured meat.
Several sources describe thesaltingof meat in the ancient Mediterranean world.Diodore of Sicilyin hisBibliotheca historicawrote that the Cosséensin the mountains ofPersiasalted the flesh of carnivorous animals.Straboindicates that people atBorsippawere catchingbatsand salting them to eat.The ancient Greeks preparedtarichos(τάριχος), which was meat and fish conserved by salt or other means.The Romans called this dishsalsamentum– which term later included salted fat, the sauces and spices used for its preparation.Also evidence of ancientsausageproduction exists. The Roman gourmetApiciusspeaks of a sausage-making technique involvingœnogaros(a mixture of the fermentedfish saucegarumwith oil or wine).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 thebutcher's.
A trade in salt meat occurred across ancient Europe. InPolybius's time (c.200 –c.118 BCE),theGaulsexportedsalt porkeach year to Rome in large quantities, where it was sold in differentcuts: rear cuts, middle cuts, hams, and sausages. This meat, after having been salted with the greatest care, was sometimes smoked. These goods had to have been considerably important, since they fed part of the Roman people and the armies. TheBelgaewere celebrated above all for the care which they gave to the fattening of their pigs. Their herds of sheep and pigs were so many, they could provide skins and salt meat not only for Rome, but also for most of Italy.TheCeretaniofSpaindrew a large export income from their hams, which were so succulent, they were in no way inferior to those ofCantabria. Thesetarichosof pig became especially sought, to the point that the ancients considered this meat the most nourishing of all and the easiest to digest.
InEthiopia, according to Pliny,and inLibyaaccording toSaint Jerome, the Acridophages (literally, the locust-eaters) salted and smoked thecricketswhich arrived at their settlements in the spring in great swarms and which constituted, it was said, their sole food.
The smoking of meat was a traditional practice in North America, wherePlains Indianshung their meat at the top of theirtipisto increase the amount of smoke coming into contact with the food.
In Europe,medieval cuisinemade 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 calledcarboucléeinRomance tonguesandbaconif it was pork.
The Middle Ages madepâtéa 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 byGace de La Bigne, mentions in the same pâté three greatpartridges, six fatquail, and a dozenlarks.Le Ménagier de Parismentions pâtés of fish, game, young rabbit, freshvenison, beef, pigeon,mutton,veal, and pork, and even pâtés of lark, turtledove, baby bird, goose, and hen.Bartolomeo Sacchi, called Platine, prefect of theVatican 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 amélangeof pepper, cinnamon and poundedlard; one studded the fat withclovesuntil it was entirely covered, then placed it inside a pâte.
In the 16th century, the most fashionable pâtés were ofwoodcock,au bec doré,chapon,beef tongue, cow feet, sheep feet, chicken, veal, and venison.In the same era,Pierre Belonnotes that the inhabitants ofCreteandChioslightly salted then oven-dried entirehares, sheep, androe deercut into pieces, and that inTurkey, cattle and sheep, cut and minced rouelles, salted then dried, were eaten on voyages with onions and no other preparation.
During theAge of Discovery, salt meat was one of the main foods for sailors on long voyages, for instance in themerchant marineor thenavy. In the 18th century, salted Irish beef, transported in barrels, were 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 properlyfeed soldiersduring long campaigns outside the country, such as in theNapoleonic Wars, and to nourish a constantly growing population often living in appalling conditions drove scientific research, but aconfectioner,Nicolas Appert, in 1795 developed through experimentation a method which became universal and in one language bears his name: airtight storage, calledappertisationin French.
With the spread ofappertisation, the 19th-century world entered the era of the "food industry", which developed new products such as canned salt meat (for examplecorned beef). The desire for safer food led to the creation of the US'sPure Food and Drug Actin 1906, followed by the national agencies for health security and the establishment offood traceabilityover the course of the 20th century.It also led to continuing technological innovation.
InFrance, the summer of 1857 was so hot that most butchers refused to slaughter animals andcharcutierslost 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 completed by 1857, which proposed some solutions: not less than 91 texts exist, of which 64 edited for only the years between 1851 and 1857.
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.
For example, the appearance in the 1980s of preservation techniques undercontrolled atmospheresparked a small revolution in the world's market for sheep meat: the lamb ofNew 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 was a sufficient duration for it to reach Europe by boat. Before, meat from New Zealand was frozen, 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.