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Curing (food preservation)

Sea salt being added to raw ham to make Prosciutto.

Bag of Prague powder, also known as "curing salt" or "pink salt." It is typically a combination of salt and sodium nitrite that is dyed pink to distinguish it from ordinary salt.

Curing is any of various food preservation and flavouring 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, the process of flavouring, or cooking. The use of food dehydration was the earliest form of food.

Food curing dates back to ancient times, both in the form of smoked meat and as salt-cured meat. The Plains Indians hung their meat at the top of their tipis to increase the amount of smoke coming into contact with the food. It was discovered in the 1800s that salt mixed with nitrates (saltpeter) would color meats red, rather than grey, and consumers at that time then strongly preferred red-coloured meat.

Chemical actions:

  • Salt

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.

  • Sugar

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 flavour,  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. Nitrate (NO3−), generally supplied by sodium nitrite or potassium nitrate, is used as a source for nitrite (NO2−). The 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 colour (nitrosomyoglobin) when raw, and the characteristic cooked-ham pink colour (nitrosohemochrome or nitrosyl-heme) when cooked. The addition of ascorbate to cured meat reduces formation of nitrosamines, but increases the nitrosylation of iron.

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, nitroso thiols 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.

Salt cured and brined products

Salt serves four main purposes in the preservation of food in the charcuterie kitchen. The first is inducing osmosis: this process involves the movement of water outside of the membranes of the cells, which in turn reabsorb the salted water back into the cell; this process assists in the destruction of harmful pathogens. The second is dehydration, which means the salt pulls excess water from the protein, which aids in the shelf-life of the protein, as there is less moisture present for bacterial growth. Fermentation is the third, in which salt assists in halting the fermentation process which would otherwise completely break the meat down. Finally, salt assists in denaturing proteins, which in essence means the structure of the proteins is effectively shifted, similar to the effects of cooking.

Before the discovery of nitrates and nitrites by German chemists around 1900, curing was done with unrefined salt and saltpeter. As saltpeter gives inconsistent results in preventing bacterial growth, nitrate and nitrite (in the form of sodium nitrite and sodium nitrate) have increased in popularity for their consistent results. Nitrates take a considerably longer period of time to break down in cured foods than nitrites; because of this, nitrates are the preferred curing salts for lengthy curing and drying periods. Nitrites are often used in foods that require a shorter curing time and are used for any item that will be fully cooked.mEventually, a portion of the nitrates will be converted into nitrites by bacterial action.

Nitrite has multiple purposes in the curing process. One purpose is flavour, the nitrites giving a sharp, piquant flavour to the meat. Second, the nitrites react with substances in the meat to produce nitric oxide. Nitric oxide prevents iron from breaking down the fat in the meat, thus halting rancidity. The binding also creates the characteristic reddish colour found in most cured meat. Finally, the nitrite inhibits the growth of botulism-causing organisms that would ordinarily thrive in the oxygen-deprived environment in the sausage casing. German scientists originally named botulism poisoning Wurstvergiftung or "sausage poisoning". The term botulism derives its name from the Latin term for sausage.

Eating cured meat products has been linked to a small increase in gastric cancer, as well as chronic obstructive pulmonary disease. The negative effects are presumed to be caused by nitrates and nitrites, as well as nitrosamines which are formed by nitrites reacting with meat. These risks are generally regarded as minimal, and regulations in the United States limit ingoing nitrites to 156 parts per million (0.0156%) (less for bacon) as a precautionary measure.

The second curing salt blend is called "prague powder II" or "insta-cure #2". Also coloured pink to differentiate it from table salt, this blend is produced from salt and sodium nitrate. This mixture is used for dry sausages that require a longer drying period which requires the presence of nitrate.

Curing salt blends

Two main types of curing salt mixture are used by the charcutier. The first is known by multiple names, including "tinted cure mix", "pink cure", "prague powder", or "insta-cure #1". The mixture is 93.75% sodium chloride and 6.25% sodium nitrite. When used, the recommended amount is a ratio of 4 oz for each 100 lb (1 kg for each 400 kg) of meat or 0.25% of the total weight of the meat. This blend is colored bright pink to keep the charcutier from confusing the mixture with regular salt.

The second curing salt blend is called "prague powder II" or "insta-cure #2". Also coloured pink to differentiate it from table salt, this blend is produced from salt and sodium nitrate. This mixture is used for dry sausages that require a longer drying period which requires the presence of nitrate.

Seasoning and flavouring agents

Sweeteners and other flavouring agents are necessary in the production of many cured products due to the harsh flavours of the salt. A number of sweeteners can be used in curing foods, including dextrose, sugar, corn syrup, honey, and maple syrup. Dextrose is seen often in cured meat, as it not only mellows the harshness, but it also increases the moisture content of the cured product while adding less sweetness to the cured meat. The sweeteners also assist in stabilizing the colors in meat and help the fermentation process by giving a nutrient to the bacteria.

Numerous spices and herbs are used in the curing process to assist with the flavour of the final product. The sweet spices regularly used include cinnamon, allspice, nutmeg, mace, and cardamom. Other flavouring agents may include dried and fresh chilies, wine, fruit juice, or vinegar.

Pickling salts (not to be confused with curing salt)

Pickling salt is a salt that is used mainly for canning and manufacturing pickles. It is sodium chloride, as is table salt, but unlike most brands of table salt, it does not contain iodine or any anti caking products added. A widely circulated legend suggested that iodisation caused the brine of pickles to a change of colour. This is false, however, some anti-caking agents are known to collect at the bottom of the jars, a minor aesthetic issue. Pickling salt is very fine-grained, to speed up dissolving in water to create a brine, so it is useful for solutions needing salt.

Other uses - pickling salt can be used for things other than pickling. It can be used in place of table salt, although it can cake. A solution to this would be to add a few grains of rice to the salt, or to bake it (draws the moisture out), and then break it apart. Pickling salt sticks well to food, so it can be used in place of popcorn salt, which also has fine grains.

Curing salt (not to be confused with pickling salt)

Curing salts are used in food preservation to prevent or slow spoilage by bacteria or fungus. Generally they are used for pickling meats as part of the process to make sausage or cured meat. Curing salts are generally a mixture of table salt and sodium nitrate. Common types of curing salts are Prague powder, which is 6% sodium nitrite and 94% table salt, and Prague powder which also includes sodium nitrate.

Types -  two types of curing salts are used in the preservation and sausage making, both called "Prague powder", and both dyed pink to help it blend better with meat and to prevent it from being confused with common table salt. Prague powder or pink salt contains 93.75% table salt and 6.25% sodium nitrite. Prague powder contains sodium nitrate in addition to sodium nitrite. The sodium nitrate found in Prague powder gradually breaks down over time into sodium nitrite, and by the time a dry cured sausage is ready to be eaten, no sodium nitrate should be left.mAs an additive, the sodium nitrite or nitrate serves to inhibit the growth of bacteria, specifically Clostridium botulinum in an effort to prevent botulism, and helps preserve the colour of cured meat.