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



5. Food Safety of Cured and Smoked Meats

5.1. Food Safety Concerns

Concern for food safety has arisen over: (1) the public’s desire for variety and healthfulness that leads them to both non-traditional foods and non-traditional processes that may lack research into their safety and (2) the emergence of new foodborne diseases that challenge the safety of traditional food preservation methods. Bacteria, yeasts and molds find meat a suitable substrate for growth, resulting in meat quality and safety deterioration. Foodborne diseases are mostly of bacterial origin and meat has been implicated in roughly one third of the foodborne outbreaks in North America (Saucier 1999). The pathogenic microorganisms representing the greatest risk with meat and poultry borne diseases are Salmonella spp., Campylobacter spp., verotoxigenic Escherichia coli, Listeria monocytogenes and Toxoplasma gondii (Saucier 1999). Consumers and home food preservers should be warned that microorganisms are ubiquitous in the environment and that pathogens may survive traditional and non-traditional food preservation techniques if they are improperly processed (Bruhn 1997).

5.1.1. Non-traditional foods and non-traditional processes

Today, consumers demand foods that are minimally processed, as "natural" as possible, and yet are convenient to use. Complicating these factors is a consumer preference toward cured and smoked foods that are processed with lower salt, lower nitrate and higher moisture levels. These parameters have a tremendous impact on the safety of a given cured/smoked food or process. Preferences for low fat and low sugar have less impact on the safety, but these factors can change the traditional curing and smoking process. It will be difficult to completely eliminate the use of nitrite, as there is no known substitute for it as a curing agent for meat. Nonetheless, the demand for fewer chemicals added to foods has put pressure on the industry and the scientific community to seek new alternatives.

In-home vacuum packaging machines have become popular in recent years. It is important to realize that in-home vacuum packaging is not a substitution for cooking or any form of food preservation, e.g., refrigeration, freezing, or curing (Andress 2001). In-home vacuum packaging can reduce the quality deterioration of foods catalyzed by oxygen, such as rancidity. Many food spoilage and food poisoning organisms require oxygen for growth and would also be inhibited by this process. However, the most deadly food poisoning organism, Clostridium botulinum requires a low oxygen atmosphere and therefore, vacuum packaging favors its growth (Andress 2001). In cured meats, careful attention must be paid to proper use of nitrates/nitrites that inhibit Clostridium botulinum prior to use of in-home vacuum packagers. To further reduce the risk of botulism after vacuum packaging, properly refrigerate the cured/smoked meats. Under normal processing, freezing of salt-cured meats is not recommended, due to oxidative rancidity that affects the quality and flavor of the product.

5.1.2. Emergence of new foodborne diseases

More than 200 known diseases are transmitted through food (Mead et al. 2000). The causes include viruses, bacteria, and parasites. Many of the pathogens causing foodborne illness were not recognized 20 years ago (Mead et al. 2000). Major emerging pathogens include Campylobacter jejuni, Salmonella, Listeria monocytogenes, and Escherichia coli O157:H7. Many emerging foodborne diseases can cause chronic and serious health problems (Mead et al. 2000).

5.2. Food Poisoning Organisms

Microorganisms are ubiquitous in foods. Some can be present and harmless. Others can be present and produce chemicals that alter the acceptability of the food, hence food spoilage. Lastly, microorganisms can be present where they themselves or the products they produce can cause food poisoning. Details on pathogenic organisms mentioned below can be found in the FDA Bad Bug Book (US FDA 1992).

5.2.1. Botulism

The majority (65%) of botulism cases are a result of inadequate home food processing or preservation (CDC 1998). Botulism results from ingestion of a toxin produced by the bacterium C. botulinum. This bacterium requires a moist, oxygen-free environment, low acidity (pH greater than 4.6) and temperatures in the danger zone (38-140°F) to grow and produce toxin. C. botulinum forms heat resistant spores that can become dangerous if allowed to germinate, grow, and produce toxin. Sufficient heat can be used to inactivate the toxin (180°F for 4 min., Kendall 1999). C. botulinum thrives in moist foods that are low in salt (less than 10%), particularly when they are stored at temperatures above 38°F. These organisms will not grow in an aerobic environment, but other aerobic organisms in a closed system can rapidly convert an aerobic environment to an anaerobic environment by using the oxygen for their own growth, permitting growth of C. botulinum.

    For more information, please refer to the following resources:
  1. Botulism in the United States, 1899 - 1996 (CDC 1998).
  2. Potential Hazards in Cold Smoked Fish: Clostridium botulinum type E. (US FDA 2001c).
  3. Botulism (Kendall 1999).

5.2.2. Clostridium perfringens

Spores of some strains of Clostridium perfringens are so heat resistant that they survive boiling for four or more hours. Furthermore, cooking drives off oxygen, kills competitive organisms, and heat-shocks the spores, all of which promote germination to vegetative or growing cells. Once the spores have germinated, a warm, moist, protein-rich environment with little or no oxygen is necessary for growth. If such conditions exist (i.e., incorrectly holding meats at warm room temperature for smoking), sufficient numbers of vegetative cells may be produced to cause illness upon ingestion of the contaminated meat product.

5.2.3. Listeria monocytogenes

L. monocytogenes has been found in fermented raw-meat sausages, raw and cooked poultry, raw meats (all types), and raw and smoked fish. Its ability to grow at temperatures as low as 3°C, permits multiplication in refrigerated foods. The organism grows in the pH range of 5.0 to 9.5 and is resistant to freezing. It is salt tolerant and relatively resistant to drying, but easily destroyed by heat. (It grows between 34 - 113°F).

    For more information, please refer to the following resources:
  1. Potential Hazards in Cold Smoked Fish: Listeria monocytogenes (US FDA 2001c).

5.2.4. E. coli O157:H7

Ground beef is the food most associated with E. coli O157:H7 outbreaks, but smoked and cured foods also have been implicated, including dry-cured salami, game meat, and homemade venison jerky. Studies have shown that E. coli O157:H7 can survive the typical dry fermentation processing conditions (Tilden and others 1996); E. coli O157:H7's tolerance of acidic conditions has also been reported in the processing of other foods such as apple cider and mayonnaise. These findings led to significant changes in the food industry and in the manufacturing of dry fermented sausage in the U.S. In August 1995, USDA/FSIS recommended using a heat process (145°F for 4 minutes) to inhibit E. coli O157:H7 growth in sausage (USDA FSIS 1995).

5.2.5. Trichinosis

Details on trichinosis can be found in a publication by the National Pork Producers Council (Gamble) and on trichinosis statistics in the USA (CDC 1988). Trichinosis is an infestation of trichinae, or Trichinella spiralis or other Trichinella spp. The parasites invade the muscles causing severe pain and edema. It can be avoided by ensuring that cooked pork or certain wild game meat reaches an internal temperature of 150°F or more. Freezing the pork according to the following chart also can kill trichinae:

Table 5.1. Freezing Pork to Kill Trichinae
Freezer Temperature Group 1 Days Group 2 Days
5°F 20 30
-10°F 10 20
-20°F 6 12
Group 1 comprises product in separate pieces not exceeding 6" in thickness or arranged on separate racks with the layers not exceeding 6" in depth. Group 2 comprises product in pieces, layers or within containers the thickness of which exceeds 6" but not 27" (US FDA 1999).

Although the incidence of trichinosis has decreased markedly from 300 to 400 cases annually in the 1940's to less than 90 cases per year in the early 1980's, this disease remains a problem in the United States. According to USDA recommendations, T. spiralis in pork is rendered non-viable if held at 5°F, a temperature achievable in noncommercial freezers, for 20 days. However, meat from wild game, such as polar bear or walrus meat that has been infected with T. spiralis, remains infective even after 24 months of storage at 0°F. The difference in susceptibility may be caused by different strains of T. spiralis found in domestic versus wild animals. Adequate cooking (170°F. internally), well above the thermal death point of the organism (137°F), remains the best safeguard against trichinosis in game meats (CDC 1985).

5.2.6. Staphylococcus aureus

Staphylococcus is more salt-tolerant than most other bacteria. It is naturally present on human skin. Some species of Staphylococcus produce toxins that cause food poisoning. So, handling of cured meats with unwashed hands, followed by holding the food at warm temperatures (>40°F), can result in bacterial growth and toxin formation. While temperatures of 120ºF can kill the bacterium itself, its toxin is heat resistant; therefore, it is important to keep the Staphylococcus organism from growing in foods. Use proper food handling practices to avoid contact with potentially contaminated surfaces and materials. Keep food either hot (above 140°F) or cold (below 40°F) during serving time, and as quickly as possible, refrigerate or freeze leftovers and foods to be served later. Staphylococcus aureus is destroyed by cooking and other thermal processing, but can be reintroduced via mishandling; the bacteria can then produce a toxin that is not destroyed by further cooking. Dry curing may or may not destroy S. aureus, but the high salt content on the exterior of dry cured meats inhibits these bacteria. When the dry cured meat is sliced, the moist, lower salt interior will permit staphylococcal multiplication.

5.2.7. Salmonella

Salmonella outbreaks have been recorded for raw meats, poultry, and fish and beef jerky. Salmonella bacteria thrive at temperatures between 40-140°F. They are readily destroyed by cooking to 165°F and do not grow at refrigerator or freezer temperatures. They do survive refrigeration and freezing, however, and will begin to grow again once warmed to room temperature.

5.2.8. Campylobacter

Raw chicken is a primary source of this organism, which grows best in a reduced oxygen environment. It is easily killed by heat (120°F), is inhibited by acid, salt and drying, and will not multiply at temperatures below 85°F. Campylobacter is the leading bacterial cause of diarrhea in the U.S.

5.2.9. Vibrio

Infections with this organism have been associated with the consumption of raw, improperly cooked, or cooked and recontaminated fish and shellfish. A correlation exists between the probability of infection and warmer months of the year. Improper refrigeration of seafood contaminated with this organism will allow its proliferation, increasing the possibility of infection. People with liver disease are particularly at risk for infection caused by undercooked seafood containing V. vulnificus (US FDA CFSAN 1998).

5.2.10. Parasites (other than Trichinella)

Anisakis simplex parasites are known to occur frequently in the flesh of cod, haddock, fluke, pacific salmon, herring, flounder, and monkfish. However, only 10 reported cases annually in the U.S. are attributed to them. Diphyllobothrium latum and Nanophyetus spp. parasites are known to occur frequently in the flesh of fish. Foodborne illnesses attributed to them are few in number. Sufficient cooking of foods would destroy the parasites.

In the Great Lakes region of the U. S., the Broad Fish Tapeworm has resulted in food poisoning outbreaks related to pickled pike. The larvae pass through small fish until they hatch as small worms in larger fish. If consumed at this stage by humans the worms can grow in the intestines (Schafer 1990). Sufficient cooking of foods would destroy the parasites.

5.2.11. Viruses

Shellfish are the food most often implicated foods in outbreaks of viruses such as Norwalk and Hepatitis A. Ingestion of raw or insufficiently steamed clams and oysters poses a high risk for infection with viruses. Sufficient cooking of foods would destroy the viruses.

5.3. Inhibition of Pathogens in Cured Meats

Salt and nitrates or nitrites are the primary chemicals that are responsible for the inhibition of pathogen growth when curing meats. Adding to that, pH and temperature (below 40°F or above 140°F), these factors can act in concert to prohibit the growth of pathogens in these foods. Table 5.3. indicates some extreme parameters for growth of pathogens.

Table 5.3. Critical Parameters for growth of some Pathogens (Corlett Jr 1998).
Organism min. pH max. % salt min. temp. oxygen req.
Campylobacter 4.9 2 86°F MA1
Clostridium 4.7 10 38°F AN2
E. coli 3.6 8 33°F FA3
Listeria 4.8 12 32°F FA
Salmonella 4.0 8 41°F FA
Staphylococcus 4.0 20 41°F FA
Vibrio 3.6 10 41°F FA
1MA=microaerophilic; requires limited levels of oxygen; 2AN=anaerobic, requires the absence of oxygen; and 3FA=facultative anaerobic, can grow either with or without oxygen.

5.4. Cured / Smoked Food Poisoning

5.4.1. Ham

Trichinella, Staphylococcus, and molds are the microorganisms most associated with ham. All ham should be processed to specifically kill trichinae (USDA FSIS 1995c). Staphylococcus aureus, which is salt tolerant, can survive the high salt levels of the ham surface. Once the ham is sliced, S. aureus can grow on the interior tissues where there is a lower salt concentration. Therefore, the USDA-FSIS recommends that all sliced ham be refrigerated (USDA FSIS 1995c). Molds can grow on the ham surface, especially on country-cured hams. The USDA-FSIS recommends that you wash the ham free of the mold with a stiff vegetable brush and that consumption of the ham is safe (USDA FSIS 1995c). We were unable to find any studies of aflatoxin formation with molds associated with hams.

    For more information:
  1. Outbreak of Type E Botulism associated with home-cured Ham Consumption (Rosetti et al. 1999).
  2. Tainted ham suspected in deadly bacteria outbreak (Associated Press 1997).
  3. Outbreak of Staphylococcal Food Poisoning Associated with Precooked Ham -- Florida, 1997 (CDC 1997b).

5.4.1. Bacon

Like other cured products, Listeria monocytogenes has been responsible for a number of recalls of ready-to-eat bacon, e.g., State of Ohio Department of Agriculture Recall Announcement (ODA/ODH) 99 05a. Packages stored at room temperature sampled positive for the pathogen.

5.4.2. Beef

Pastrami made in a small Idaho commercial firm tested positive for Listeria monocytogenes in July 2000. No reports of food poisonings were recorded, but the products were recalled (USDA FSIS 2000a). Corned beef samples also tested positive for Listeria monocytogenes from a Michigan commercial firm (USDA FSIS 2000b). Corned beef was cooked and temperature abused at a deli in Ohio resulting in an outbreak of C. perfringens food poisoning (CDC 1994).

    For more information, please refer to the following resources:
  1. Clostridium perfringens Gastroenteritis Associated with Corned Beef Served at St. Patrick's Day Meals -- Ohio and Virginia, 1993 (CDC 1994).

5.4.3. Poultry

Much of the reports of food poisoning and recalls of poultry products for have been with commercial ready to eat products, such as chicken or turkey lunchmeats.

5.4.4. Fish

Listeria monocytogenes has been found in commercial samples of cold smoked fish leading to product recalls in New York (Cold smoked sea bass FDA Recall No.F-313-1) and Seattle, WA (Cold smoked salmon FDA Recall #F-265-1). These recalls demonstrate that even with HACCP and careful plant sanitation, commercial processors have contamination incidences in their cold smoked fish processes. In New York, fish sausage was recalled because laboratory analysis found pH (acidity), salt and water activity levels in the product were such that they could potentially permit Clostridium botulinum to develop and produce the toxin (NY State Agriculture Commissioner 2000).

    For more information, please refer to the following resources:
  1. Uneviscerated Fish Products that are Salt cured, Dried, or Smoked (US FDA 2000).
  2. International Outbreak of Type E Botulism Associated With Ungutted, Salted Whitefish (CDC 1987).
  3. Vibrio parahaemolyticus Infections Associated with Eating Raw Oysters -- Pacific Northwest, 1997 (C.D.C. 1997c).
  4. Vibrio vulnificans (US FDA CFSAN 1998).
  5. Processing Parameters Needed to Control Pathogens in Cold Smoked Fish (US FDA 2001c).

5.4.5. Sausage

Recent concern about the safety of sausages has been in the semi-dry fermented sausages, such as summer sausage. E. coli O157:H7 has been found to survive the acidity of these products (Corlett 1998). Some commercial, ready-to-eat sausages and luncheon meats have been implicated in Listeria monocytogenes growth and outbreaks. Additional concerns with trichinae may occur in any pork sausage.

    For more information, please refer to the following resources:
  1. Pennsylvania Firm Recalls Lebanon Bologna Nationwide (Lombardi and Redding 1995).
  2. Illness outbreak associated with Escherichia coli O157:H7 in Genoa salami (William and others 2000).
  3. A new route of transmission for Escherichia coli: infection from dry fermented salami (Tilden and others 1996).
  4. Interim Guidelines for the Control of Verotoxinogenic Escherichia coli Including E. coli O157:H7 in Ready to Eat Fermented Sausages Containing Beef or a Beef Product as an Ingredient: Guideline no. 12 (Health Products and Food Branch - Canada 2000).
  5. Escherichia coli O157:H7 Outbreak Linked to Commercially Distributed Dry-Cured Salami -- Washington and California, 1994 (CDC 1994).

5.4.6. Game

Precaution should be used since venison, bear, elk, wild boar, wild turkey, rabbit and other game animals are usually field dressed in unknown sanitary conditions or kept from immediate refrigeration. Two areas of special interest should be noted: (1) E. coli O157:H7 outbreaks in game sausage and jerky, and (2) Trichinosis in game meats from northern U.S. areas (Zarnke and others 1997). Several outbreaks of E. coli O157:H7 have occurred in venison jerky (USDA FSIS 1998).

T. nativa is an Alaskan, Canadian, and Arctic strain of Trichinella that is freeze-resistant. Unlike pork, freezing arctic meat will not kill larval cysts. Wild game, e.g., bear or walrus meat, is safe once the entire piece is completely cooked. USDA recommends attaining an internal temperature of at least 170°F (CDC 1985). Since cooking may be uneven, microwaving of game meats is not recommended, (Zarnke and others 1997).

    For more information, please refer to the following resources:
  1. Five Cases of Trichinosis - Why Bear Meat Must Be Thoroughly Cooked (State of Alaska Epidemiology 2000).
  2. E. coli Cases Associated with Wild Game Pepperoni (Idaho Central District Health Department 1999).
  3. An outbreak of E. coli O157:H7 infections traced to jerky made from deer meat (Oregon Health Division 1997).

5.5. Cured/Smoked Food Spoilage

Not all microbial growth leads to food poisoning. Indeed, many organisms simply spoil cured and smoked foods making them unpalatable. Keep in mind that it is a general rule that if conditions exist to allow growth of spoilage organisms, these same conditions can allow for the growth of food poisoning organisms. Good judgment should prevail.

5.5.1. Lactic Acid Bacteria

Lactic acid bacteria are frequent spoilage organisms on cured/smoked meats. They are tolerant of some of the conditions in the curing/smoking process or are contaminates after processing. They grow slowly, but eventually spoil the food by producing organic acids.

5.5.2. Mold and Cured Meats

Moldy cured or smoked meat is a controversial topic. Very often country hams will have a moldy surface. Currently the USDA FSIS recommends cleaning the mold and soaking the ham in water to refresh it is a safe procedure (USDA FSIS 1995c). Other suggestions are to wash the ham in acetic acid (acetic acid Avinegar@ 10% in water; Marriott and Graham 2000).

5.5.3. Greening of Cured/Smoked Meats

Lactobacillus viridescens, or similar bacteria that produce hydrogen peroxide may cause greening in meats. The H2O2 reacts with myoglobin to produce a green sheen pigment. The meat, while less appealing, is not dangerous to consume.

5.5.4. Slime Producers

Some Micrococcus spp. and other bacteria are capable of producing slime on the surface of hams, bacon, and sausages.

5.5.5. Gas Producers

Some organisms can produce gas pockets inside cured and/or smoked meats.

5.5.6. Rancid Flavors in Home Cured Pork

Salt increases oxidation during long cures and can lead to a rancid flavor. Prolonged frozen storage may also contribute to oxidation leading to rancid flavors. Many consumers prefer these flavors. For those that do not, shorter curing and aging times should be considered (Marriott and Graham 2000).

    For more information, please refer to the following resources:
  1. Some Solutions To Difficulties of Home-Curing Pork (Marriott and Graham 2000).
  2. Protecting Home-cured Meat from Insects and Mites (Townsend 1997).


Document Use | Preface | Table of Contents | References