Trichinae

Trichinae is an illness caused by the consumption of raw or undercooked pork or wild game meat infected with “trichinella spiralis”. It is a round worm that can migrate from the digestive tract and settle in the form of cycts in various muscles of the body. The disease is almost non-existent in American pork due to their strictly controlled feed, but it can still be found in other meats like horse, dog or wild game. Generally pigs become infected by eating raw garbage which is illegal. Of much greater risk is exposure of pigs to rodents and wildlife that is often infected with trichinae. Pigs which are free to to range outdoors can occasionally find carcasses which they might chew on. The strictest inspection requirements are in place in Europe and countries like Denmark and the Netherlands consider themselves free of trichinae. The illness is not contagious and the food has to be consummed first. The first symptoms appear within 1-2 days of eating contaminated meat. They include nausea, diarrhea, vomiting, abdominal pain, itchy skin, and may be mistaken for the flu. Trichinae in pork is killed by raising its internal temperature to 137º F (58º C). The U.S. Code of Federal Regulations requires pork to be cooked for 1 minute at 140º F (60º C), the U.S. Department of Agriculture recommends to cook fresh pork to an internal temperature of 160º F (71º C) and The National Pork Producers Council recommends an internal cooking temperature of 155º F (68º C) for maximum juiciness and flavor.

Trichinae is also killed by storing pork at low temperatures. The U.S. Department of Agriculture’s Code of Federal Regulations, Title 9, Volume 2, Cite: 9 CFR318.10 requires that pork intended for use in processed products be frozen at:

Group 1
comprises product in separate pieces not exceeding 6” (15 cm) in thickness, or arranged on separate racks with layers not exceeding 6” (15 cm) in depth, or stored in crates or boxes not exceeding 6” (15 cm) in depth, or stored as solidly frozen blocks not exceeding 6” (15 cm) in thickness.
Group 2
comprises product in pieces, layers, or within containers, the thickness of which exceeds 6” (15 cm) but not 27” (68 cm) and product in containers including tierces, barrels, kegs, and cartons having a thickness not exceeding 27” (68 cm).

Table 1. Required Period of Freezing Indicated

Fahrenheit Celsius Days Group 1 Days Group 2
5 -15 20 30
-10 -23.3 10 20
-20 -28.9 6 12

The product undergoing such refrigeration or the containers thereof shall be so spaced while in the freezer as will insure a free circulation of air between the pieces of meat, layers, blocks, boxes, barrels, and tierces in order that the temperature of the meat throughout will be promptly reduced to not higher than 5º F (-15º C), -10º F (-23.3º C), or -20º F (-28.9º C), as the case may be. In lieu of the methods prescribed in Table 1, the treatment may consist of commercial freeze drying or controlled freezing, at the center of the meat pieces, in accordance with the times and temperatures specified in Table 2 to be found in the Prescribed treatment of pork and products containing pork to destroy trichinae.

Microwaving, curing, drying or smoking is not effective in preventing Trichinae. It should be noted that freezing will not kill larval cysts in bears and other wild game that live in Northwestern U.S. and Alaska. That meat has to be cooked to 160º F (72º C) internal temperature.

Trichinae Control in Dry Meat products

Pork products which are not cooked such as slow fermented and dried sausages are at risk of being infected with trichinae. Cured hams and butts fit into the same category and must be dealt with differently. Although it is possible to obtain certified pork trichinae free it is not something that is universally done as it requires laboratory tests. Curing meats with salt according to USDA regulations takes care of the problem. Hams were cured with salt long before USDA came to be and the procedures used in the past took care of the trichinae problem. As explained earlier, freezing pork meat is an approved method for treating trichinae and it can be applied at home. It is not practical for large scale production as it will require investment in time and space plus additional electricity costs. In addition frozen meat exhibits damaged sell structure due to the growth of ice crystals. That will affect the texture and sliceability of the finished ham. The best solution is to use enough salt what will remove moisture, slow the growth of bacteria and will eliminate trichinae problem. Most prescribed procedures call for 3.3% salt for dry sausages and 4-5% salt for large whole meats like shoulders and hams. Those amounts, which are usually applied anyhow, will cure meats and will treat it for trichinae at the same time. Keep in mind that pork used in fermented spreadable sausages should be treated for trichinae by freezing.

Treatment of Pork to Destroy Trichinae

From the Code of Federal Regulations:

Title 9: Animals and Animal Products PART 318 - ENTRY INTO OFFICIAL ESTABLISHMENTS; REINSPECTION AND PREPARATION OF PRODUCTS

§ 318.10 Prescribed treatment of pork and products containing pork to destroy trichinae.

Minimum Internal Temperature ° F Minimum Internal Temperature ° C Minimum Time
120 49.0 21 hours
122 50.0 9.5 hrs
124 51.1 4.5 hrs
126 52.2 2 hrs
128 53.4 1 hr
130 54.5 30 minutes
132 55.6 15 min
134 56.7 6 min
136 57.8 3 min
138 58.9 2 min
140 60.0 1 min
142 61.1 1 min
144 62.2 Instant

Table 1. Required Period of Freezing Indicated

º F º C Days Group 1 Days Group 2
5 -15 20 30
-10 -23.3 10 20
-20 -28.9 6 12

Table 2 — Alternate Periods of Freezing at Temperatures Indicated

Maximum Internal Temperature ° F Maximum Internal Temperature ° C Minimum Time
0 -17.8 106 hours
-5 -20.6 82 hours
-10 -23.3 63 hours
-15 -26.1 48 hours
-20 -28.9 35 hours
-25 -31.7 22 hours
-30 -34.5 8 hours
-35 -37.2 1/2 hour

Table 3A - Sausage Drying Room Times by Method No. 6

Diameter of casing at time of stuffing (1*) Days in drying room (2*)
1 inches 14
1½ inches 15
2 inches 16
2½ inches 18
3 inches 20
3½ inches 23
4 inches 25
4½ inches 30
5 inches 35
5½ inches 43
6 inches 50

Table 3B - Percentage Reduction in Drying Room Time (Table 3A) Permitted by Holding Times and Temperatures Prior to Drying (*1)

Min. Time in hours Degree ° F
70° 75° 80° 85° 90° 95° 100° 105° 110° 120°
Degree ° C
21.1° 23.9° 26.7° 29.5° 32.2° 35.0° 37.9° 40.6° 43.3° 48.9°
24 4% 5% 8% 10% 15% 23% 37% 57% 90% (*3)100%
48 9% 12% 18% 25% 35% 49% 88% (*3)100% (*3)100% (*3)100%
72 14% 19% 28% 39% 55% 74% (*3)100% (*3)100% (*3)100% (*3)100%
96 19% 26% 38% 53% 75% 98% (*3)100% (*3)100% (*3)100% (*3)100%
120 24% 33% 48% 67% 95% (*3)100% (*3)100% *(3)100% (*3)100% (*3)100%

Table 4 - Reduced Salt Content - Drying Room Times [Required percentage increase in drying room time (table 3A) for added salt of less than 3.33 pounds per hundredweight of sausage]

Minimum pounds of salt added to sausage(*1) Increase in drying room time(*2)
3.3 1
3.2 4
3.1 7
3.0 10
2.9 13
2.8 16
2.7 19
2.6 22
2.5 25
2.4 28
2.3 31
2.2 34
2.1 37
2.0 40

Treatment Schedule for Sausages 105 Millimeters (4⅛ Inches) or Less in Diameter

Minimum chamber temperature ° F Minimum chamber temperature ° C Minimum time (hours)
50 10 12
90 32.2 1
100 37.8 1
110 43.3 1
120 48.9 1
125 51.7 7

Treatment Schedule for Sausages 55 Millimeters (2⅛ Inches) or Less in Diameter

Minimum chamber temperature ° F Minimum chamber temperature ° C Minimum time (hours)
50 10 12
100 37.8 1
125 51.7 6

Monthly Temperatures (°F) for Boone NC, 1951–1980

Jan Feb Mar Apr May June July Aug Sep
Normal average temperatures
32.2 34.1 41.3 51.2 59.1 65.1 68.3 67.5 61.6
Normal minimum temperatures
22.8 24.2 30.8 39.6 48.1 54.7 58.5 57.6 51.6

Table 5. Drying Times and Temperatures for Trichina Inactivation in Hams and Shoulders *

Minimum Drying Temperature Minimum days at drying temperature Fractional period for one day of drying ° F ° C
° F ° C
130 54.4 1.5 .67
125 51.7 2 .50
120 48.9 3 .33
115 46.1 4 .25
110 43.3 5 .20
105 40.6 6 .17
100 37.8 7 .14
95 35.0 9 .11
90 32.2 11 .091
85 29.4 18 .056
80 26.7 25 .040
75 23.9 35 .029

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