The National Center for Home Food Preservation
Guide and Literature Review Series:
Smoking and Curing

 
 

Curing and Smoking Meats for Home Food Preservation
Literature Review and Critical Preservation Points


Document Use | Preface | Table of Contents | References



2. Curing Foods

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

2.1. Salting / Corning

Salt inhibits microbial growth by plasmolysis. In other words, water is drawn out of the microbial cell by osmosis due to the higher concentration of salt outside the cell. A cell loses water until it reaches a state first where it cannot grow and cannot survive any longer. The concentration of salt outside of a microorganism needed 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, whereas other types are able to survive in much higher salt concentrations, e.g., up to 20% salt for Staphylococcus or up to 12% salt for Listeria monocytogenes (Table 5.3.). 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 accomplished by adding salt dry or in brine to meats. Dry salting, also called corning originated in Anglo-Saxon cultures. Meat was dry-cured with coarse "corns" or pellets of salt. Corned beef of Irish fame is made from a beef brisket, although any cut of meat can be corned. Salt brine curing involves the creation of brine containing salt, water and other ingredients such as sugar, erythorbate, or nitrites. Age-old tradition was to add salt to the brine until it floated an egg. Today, however, it is preferred to use a hydrometer or to carefully mix measured ingredients from a reliable recipe. Once mixed and placed into a suitable container, the food is submerged in the salt brine. Brine curing usually produces an end product that is less salty compared to dry curing. Injection of brine into the meat can also speed the curing process.

2.2. Nitrate/ 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 1800's it was realized that saltpeter (NaNO3 or KNO3) present in some impure curing salt mixtures would result in pink colored meat rather than the typical gray color attained with a plain salt cure. This nitrate/nitrite in the curing process was found to inhibit growth of Clostridium. Recent evidence indicates that they may also inhibit E. coli, Salmonella, and Campylobacter if in sufficient quantities (Condon 1999, Doyle 1999).

Several published studies indicated that N-nitrosoamines were considered carcinogenic in animals. For this reason, nitrate is prohibited in bacon and the nitrite concentration is limited in other cured meats. In other cured foods, there is insufficient scientific evidence for N-nitrosamine formation and a link to cancer (Pariza 1997).

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

2.3. Cure Mixtures

For the home food preserver, measuring small batches of cure for nitrites or nitrates would require an analytical scale that few consumers have access to. Therefore, some manufacturers sell premixed salt and nitrate/nitrite curing mixes for easy home use. Caution is needed when using pure saltpeter instead of commercially prepared mixes, since accidental substitution of saltpeter for table salt in recipes can result in lethal toxic levels (Borchert and Cassens 1998).

Some examples of commercially prepared cures include:

2.3.1. Prague Powder #1, Insta Cure, or Modern Cure.

This cure contains sodium nitrite (6.25%) mixed with salt (93.75%). Consumers are recommended to use 1 oz. for every 25 lb. of meat or one level teaspoon of cure for 5 lb. of meat.

2.3.2. Prague Powder #2

This mix is used for dry cured meats that require long (weeks to months) cures. It contains 1 oz. of sodium nitrite and 0.64 oz. of sodium nitrate. It is recommended that this cure be combined with each 1 lb. of salt and for products that do not require cooking, smoking, or refrigeration. This cure, which contains sodium nitrate, acts like a time-release cure, slowly breaking down into sodium nitrite, then into nitric oxide. The manufacturer recommends using 1 oz. of cure for 25 lbs. of meat or one level teaspoon of cure for 5 lbs. of meat.

2.3.3. Mixes

Many individual manufacturers and commercial sausage makers produce curing mixtures, often combining sugar and spices with the salt and nitrite/nitrates. It is important that consumers follow manufacturer directions carefully.

For more information, please refer to the following products, companies, and available resources:

  1. Morton Salt Meat Curing Products (Morton Salt Co. 2001). Their products include Tender Quick, Sugar Cure, and Smoke Flavored Sugar Cure.
  2. Curing Products (Mandeville Co. 2001). Their products include Poultry Cure, Quick Cure, Golden Cure, Complete Cure, Maple Flavor Cure, and Myco Pickle.

2.3.4. Saltpeter, Sodium or Potassium Nitrate

Commercially, nitrate is no longer allowed for use in curing of smoked and cooked meats, non-smoked and cooked meats, or sausages (US FDA 1999). However, nitrate is still allowed in small amounts in the making of dry cured uncooked products. Home food preservers should avoid the direct use of this chemical and opt for the mixtures described above.

2.4. Combination Curing

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

2.5. Flavor of Cured Meats

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

2.5.1 Salt

Because of the amount of salt used in most curing processes, the salt flavor is the most predominant.

2.5.2. Sugar

Sugar is a minor part of the composite flavor, with bacon being an exception. Because of the tremendous amount of salt used, sugar serves to reduce the harshness of the salt in cured meat and enhance the sweetness of the product (ie. Sweet Lebanon Bologna). Sugar also serves as a nutrient source for the flavor-producing bacteria of meat during long curing processes.

2.5.3. Spices and Flavor Enhancers

Spices add characteristic flavors to the meats. Recent studies have suggested that some spices can have added preservative effects (Doyle 1999). However, the quantities of spice needed to achieve these effects may be well beyond the reasonable quantities of use.

2.5.4. Nitrates/Nitrites

Nitrites and nitrate conversion to nitrite provide the characteristic cured flavor and color (see below).

2.5.5. Fermentation

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

2.5.6. Smoking

The process of smoking gives the product the characteristic smoky flavor that can be varied slightly with cure recipes and types of smoke used.

2.6. Color of Cured Meats

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

Generation of Nitric Oxide (NO):

(1)
(2)
(3)
NaNO3
----->
NaNO2
----->
HONO
----->
NO

  1. Sodium nitrate is reduced to sodium nitrite by microorganisms such as Micrococcus spp. present on meats.
  2. 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).
  3. Nitrous acid forms nitric oxide. Nitric oxide reacts with myoglobin (meat pigments) to form a red color.

The time required for a cured color to develop may be shortened with the use of cure accelerators, e.g., ascorbic acid, erythorbic acid, or their derivatives. Cure accelerators tend to speed up chemical conversion of nitric acid to nitric oxide. They also serve as oxygen scavengers, which slow the fading of the cured meat color in the presence of sunlight and oxygen. Some studies have indicated that cure accelerators have antimicrobial properties, especially for the newly emerging pathogens like E. coli O157:H7 and Listeria monocytogenes (Doyle 1999). Since cure accelerators are rarely used in home curing, this information needs further review or research to determine what benefits home curing would have by using certain cure accelerators.


Document Use | Preface | Table of Contents | References