Curing and smoking to preserve food at home

What is cured meat?

Curing is the addition to meats of some combination of salt, sugar, nitrite and/or nitrate for preservation, flavor and color purposes. Some publications distinguish the use of salt alone as salting, and reserve the word cure for the use of salt with nitrates/nitrites. Curing ingredients can be rubbed onto the surface of the food, mixed into dry foods (dry curing), or dissolved in water (brine, wet curing, or pickling). In the last processes, the food is submerged in the brine until it is completely covered. With large cuts of meat, brine can also be injected into the muscle. The term pickle in curing has been used to mean any brine solution or a brine curing solution with added sugar.

Salting

Salt inhibits microbial growth by plasmolysis. In other words, water is removed from the microbial cell by osmosis due to the higher salt concentration outside the cell. A cell loses water until it reaches a state where it cannot grow and can no longer survive. The salt concentration outside a microorganism required to inhibit growth by plasmolysis depends on the genus and species of the microorganism. The growth of some bacteria is inhibited by salt concentrations as low as 3%, e.g. Salmonella, while other types are able to survive at much higher concentrations, e.g. up to 20% salt for Staphylococcus or up to 12% salt for Listeria monocytogenes. Fortunately, the growth of many undesirable organisms normally found in cured meat and poultry products is inhibited at relatively low concentrations of salt (USDA FSIS 1997a).

Salting can be done by adding dry or brine salt to the meat. Dry salting originates from Anglo-Saxon cultures. The meat was dry cured with coarse “grains” or pellets of salt. Brine curing involves creating a brine containing salt, water and other ingredients such as sugar, erythorbate or nitrites. The ancient tradition was to add salt to the brine until an egg floated. Today, however, it is preferable to use a hydrometer or carefully mix measured ingredients from a reliable recipe. Once mixed and placed in a suitable container, the food is submerged in the brine. Brine curing generally produces a less salty end product compared to dry curing. Injecting brine into meat can also speed up the curing process.

Nitrate and nitrite curing

Most salt cures do not contain sufficient levels of salt to preserve meats at room temperature and Clostridium botulinum spores can survive. In the early 1800s, it was realized that the saltpeter (NaNO3 or KNO3) present in some impure salt mixtures would result in pink-colored meat, rather than the typical gray color obtained with a simple salt cure. This nitrate/nitrite in the curing process has been found to inhibit the growth of Clostridium. Recent evidence indicates that they can also inhibit E. coli, Salmonella and Campylobacter if in sufficient quantities (Condon 1999, Doyle 1999).

Published studies indicated that N-nitrosoamines were considered carcinogenic in animals. For this reason, the concentration of nitrite is limited in cured meats.

For more information, see the following publications:
Examination of Dietary Recommendations for Salt-Cured, Smoked, and Nitrite-Preserved Foods (Pariza 1997).
Nitrite in Meat (Epley et al.1992).
Safety of Cured Pork Products (Cassens 2001).

Curing salt

To preserve meat at home, measuring grams or milligrams of nitrites or nitrates would require a scale that few consumers have access to. Therefore, some manufacturers sell salt and nitrate/nitrite mixtures for ease of home use, which are called curing salts. Caution is necessary when using pure saltpeter, nitrite, or nitrate rather than commercially prepared mixtures, as accidental substitution of them for table salt in recipes can result in lethal toxic levels (Borchert and Cassens 1998).

Examples of commercially prepared curing salts include: Some familiar names are Hungarian Powder, Prague Salt, Instacure, or Curing Salt. Generally these products for the curing process contain sodium nitrite (6.25%) mixed with salt (93.75%) and some variations of these combinations with sodium nitrate (4%). In these proportions, it is recommended that consumers use 2.4g for every 1kg of meat.

Combined preservation

Some current recipes for healing have vinegar, citrus juice, or alcohol as ingredients for flavor. Adding these chemicals in sufficient quantities can contribute to the preservation of the food being cured.

Taste of Cured Meats

In addition to preservation, the curing process introduces the desired flavor and color. The flavor of cured meat is thought to be a composite result of the flavors of curing agents and those developed by bacterial and enzymatic action.

Sugar

Sugar is a minor part of the flavor, with bacon being an exception. Sugar also serves to reduce the hardness of the salt in the cured meat and increase the sweetness of the product. Sugar also serves as a source of nutrients for flavor-producing meat bacteria (starter culture) during long curing processes.

Spices

Spices add characteristic flavors to meats. Recent studies have suggested that some spices may have additional preservative effects (Doyle 1999). However, the amounts of seasoning needed to achieve these effects may be far beyond reasonable usage amounts.

Fermentation

The tangy flavor seen in dry-fermented sausages such as salami is the result of bacterial fermentation or the addition of chemicals such as glucono-δ(delta)-lactone.

Smoking

The smoking process gives the product its characteristic smoky flavor, which may vary slightly depending on the curing recipes and types of wood used.

Color of Cured Meats

A high salt concentration promotes the formation of an unattractive gray color in some meats. Nitrate, when used in some uncooked, dry-cured meats, is reduced to nitrite and then to nitric oxide, which reacts with myoglobin (muscle pigment) to produce the red or pink color. If nitrite is used as the curing agent, there is no need for the nitrate reduction step, and curing color development is much faster.

Reduction of Nitrate (NaNO3) to Nitric Oxide (NO):

NaNO3 —–> NaNO2 —–> HONO —–> NO

• Sodium nitrate is reduced to sodium nitrite by microorganisms such as Micrococcus spp. present in meat.
• Sodium nitrite is reduced to nitrous acid in the presence of an acidic environment (e.g. by fermentation or by addition of glucono-δ(delta)-lactone).
• Nitrous acid forms nitric oxide. Nitric oxide reacts with myoglobin (meat pigments) to form a red color.

The time required for the development of a cured color can be reduced by using curing accelerators, for example, ascorbic acid, erythorbic acid or their derivatives. Healing accelerators tend to speed up the chemical conversion of nitric acid to nitric oxide. They also serve as oxygen scavengers, which decrease color fading of cured meat in the presence of sunlight and oxygen. Some studies have indicated that healing accelerators have antimicrobial properties, especially for pathogens such as Escherichia coli and Listeria monocytogenes.

Translated from: https://nchfp.uga.edu/publications/nchfp/lit_rev/cure_smoke_cure.html