If you smoke and vac-pack the ham then pasteurize in the sous-vide, it's good for......
"from Baldwin's tutorial"....
1. Food Safety
Non-technical Summary
You cook food to make it safe and tasty. Sous vide cooking is no different: you just have more control over both taste and safety. In sous vide cooking, you pick the temperature that equals the doneness you want and then you cook it until it’s safe and has the right texture.
Raw food often has millions of microorganisms on or in it; most of these microorganisms are spoilage or beneficial bacteria and won’t make you sick. But some of these microorganisms are pathogens that can make you sick if you eat too many of them. Most food pathogens are bacteria, but some are viruses, funguses, and parasites. Your yogurt, aged cheese, and cured salami can have hundreds of millions of spoilage or beneficial bacteria in every serving; but they don’t make you sick because spoilage and beneficial bacteria are distinct from pathogens. Since pathogens don’t spoil food, you can’t see, smell, or taste them.
While there are many ways to kill food pathogens, cooking is the easiest. Every food pathogen has a temperature that it can’t grow above and a temperature it can’t grow below. They start to die above the temperature that they stop growing at and the higher above this temperature you go, the faster they die. Most food pathogens grow fastest a few degrees below the temperature that they start to die. Most food pathogens stop growing by 122°F (50°C), but the common food pathogen
Clostridium perfringens can grow at up to 126.1°F (52.3°C). So in sous vide cooking, you usually cook at 130°F (54.4°C) or higher. (You could cook your food at slightly lower temperatures, but it would take you a lot longer to kill the food pathogens.)
While there are a lot of different food pathogens that can make you sick, you only need to worry about killing the toughest and most dangerous. The three food pathogens you should worry about when cooking sous vide are the
Salmonella species,
Listeria monocytogenes, and the pathogenic strains of
Escherichia coli.
Listeria is the hardest to kill but it takes fewer
Salmonella or
E. coli bacteria to make you sick. Since you don’t know how many pathogens are in your food, most experts recommend that you cook your food to reduce:
Listeria by at least a million to one;
Salmonella by ten million to one; and
E. coli by a hundred thousand to one. You can easily do this when you cook sous vide: you just keep your food in a 130°F (54.4°C) or hotter water bath until enough bacteria have been killed.
How long does it take for you to reduce, say,
Listeria by a million to one? Your water bath temperature is very important: when cooking beef, it’ll take you four times longer at 130°F (54.4°C) as it does at 140°F (60°C). What you are cooking is also important: at 140°F (60°C), it’ll take you about 60% longer for chicken as it does for beef. Other things, like salt and fat content, also affect how long it takes; but these difference are small compared with temperature and species.
Since sous vide cooking in a water bath is very consistent, I’ve calculated the worst-case cooking times so you don’t have to. My worst-case cooking times are based on the temperature, thickness, and type of the food and will give at least a million to one reduction in
Listeria, a ten million to one reduction in
Salmonella, and a hundred thousand to one reduction in
E. coli:
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- Table 3.1 has the pasteurization times for fish;
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- Table 4.1 has the pasteurization times for poultry; and
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- Table 5.1 has the pasteurization times for meat (beef, pork, and lamb).
Thick pieces of food, like a rib-roast, take much longer to cook and cool than thin pieces of food: a steak that is twice as thick takes about four times longer to cook and cool! So unless you are cooking a rib-roast for a party, you should cut your food into individual portions that can be cooled quickly and easily. It’s important that your pouches of food do not crowd or overlap each other in your water bath and are completely under the water; otherwise my tables will underestimate the cooking time.
If you’re not going to eat all your food immediately, then you need to know that some bacteria are able to make spores. Spores themselves will not make you sick, but they can become active bacteria that could. Cooking to kill active bacteria like
Listeria,
Salmonella, and
E. coli will leave these spores unharmed. If you keep your food hot, then the spores will not become active bacteria. But when you cool your food, the spores can become active bacteria: if you cool your food too slowly or store it for too long, then these active bacteria can multiply and make you sick. To keep these spores from becoming active bacteria, you must quickly cool your food – still sealed in its pouch – in ice water that is at least half ice until it’s cold all the way through. You can then store your food in your refrigerator for a few days or freeze it for up to a year.
Table 1.1 has approximate cooling times in ice water based on thickness and shape.
Foods you’ve pasteurized must either be eaten immediately or rapidly chilled and refrigerated to prevent the outgrowth and multiplication of spores. Moreover, the center of the food should reach 130°F (54.4°C) within 6 hours to prevent the toxin producing pathogen
Clostridium perfringens from multiplying to dangerous levels (Willardsen et al., 1977).
Raw or unpasteurized food must never be served to highly susceptible or immune compromised people. Even for immune competent individuals, it’s important that raw and unpasteurized foods are consumed before food pathogens have had time to multiply to harmful levels. With this in mind, the US Food Code requires that such food can only be between 41°F (5°C) and 130°F (54.4°C) for less than 4 hours (FDA, 2009, 3-501.19.B).
Pasteurization is a combination of both temperature and time. Consider the common food pathogen
Salmonella species. At 140°F (60°C), all the
Salmonella in a piece of ground beef doesn’t instantly die – it is reduced by a factor ten every 5.48 minutes (Juneja et al., 2001). This is often referred as a one decimal reduction and is written D606.0 = 5.48 minutes, where the subscript specifies the temperature (in °C) that the D-value refers to and the superscript is the z-value (in °C). The z-value specifies how the D-value changes with temperature; increasing the temperature by the z-value decreases the time needed for a one decimal reduction by a factor ten. So, D666.0 = 0.55 minutes and D546.0 = 54.8 minutes. How many decimal reductions are necessary depends on how contaminated the beef is and how susceptible you are to
Salmonella species – neither of which you’re likely to know. FSIS (2005) recommends a 6.5 decimal reduction of
Salmonella in beef, so the coldest part should be at least 140°F (60°C) for at least 6.5D606.0 = 35.6 minutes.
Pathogens of Interest
Sous vide processing is used in the food industry to extend the shelf-life of food products; when pasteurized sous vide pouches are held at below 38°F (3.3°C), they remain safe and palatable for three to four weeks (Armstrong and McIlveen, 2000; Betts and Gaze, 1995; Church, 1998; Creed, 1995; González- Fandos et al., 2004, 2005; Hansen et al., 1995; Mossel and Struijk, 1991; Nyati, 2000a; Peck, 1997; Peck and Stringer, 2005; Rybka-Rodgers, 2001; Simpson et al., 1994; Vaudagna et al., 2002).
The simplest and safest method of sous vide cooking is cook-hold: the raw (or partially cooked) ingredients are vacuum sealed, pasteurized, and then held at 130°F (54.4°C) or above until served. While hot holding the food will prevent any food pathogens from growing, meat and vegetables will continue to soften and may become mushy if held for too long. How long is too long depends on both the holding temperature and what is being cooked. Most foods have an optimal holding time at a given temperature; adding or subtracting 10% to this time won’t change the taste or texture noticeably; holding for up to twice this time is usually acceptable.
For cook-hold sous vide, the main pathogens of interest are the
Salmonella species and the pathogenic strains of
Escherichia coli. There are, of course, many other food pathogens but these two species are relatively heat resistant and require very few active bacteria (measured in colony forming units, CFU, per gram) to make you sick. Since you’re unlikely to know how contaminated your food is or how many of these bacteria your (or your guests) immune system can handle, most experts recommend a 6.5 to 7 decimal reductions of all
Salmonella species and a 5 decimal reduction of pathogenic
E. coli.
The most popular methods of sous vide cooking are cook-chill and cook-freeze – raw (or partially cooked) ingredients are vacuum sealed, pasteurized, rapidly chilled (to avoid sporulation of
C. perfringens (Andersson et al., 1995)), and either refrigerated or frozen until reheating for service. Typically, the pasteurized food pouches are rapidly chilled by placing them in an ice water bath for at least the time listed in Table 1.1.
For cook-chill sous vide,
Listeria monocytogenes and the spore forming pathogenic bacteria are our pathogens of interest. That’s because
Listeria is the most heat resistant non-spore forming pathogen and can grow at refrigerator temperatures (Nyati, 2000b; Rybka-Rodgers, 2001), but appears to require more bacteria to make you sick than
Salmonella or
E. coli. Most experts recommend a 6 decimal reduction in
Listeria if you don’t know the contamination level of your food.
While keeping your food sealed in plastic pouches prevents recontamination after cooking, spores of
Clostridium botulinum,
C. perfringens, and
B. cereus can all survive the mild heat treatment of pasteurization. Therefore, after rapid chilling, the food must either be frozen or held at
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- below 36.5°F (2.5°C) for up to 90 days,
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- below 38°F (3.3°C) for less than 31 days,
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- below 41°F (5°C) for less than 10 days, or
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- below 44.5°F (7°C) for less than 5 days
to prevent spores of non-proteolytic
C. botulinum from outgrowing and producing deadly neurotoxin (Gould, 1999; Peck, 1997).
A few sous vide recipes use temperature and time combinations which can reduce non-proteolytic
C. botulinum to a safe level; specifically, a 6 decimal reduction in non-proteolytic
C. botulinum requires 520 minutes (8 hours 40 minutes) at 167°F (75°C), 75 minutes at 176°F (80°C), or 25 minutes at 185°F (85°C) (Fernández and Peck, 1999). The food may then be stored at below 39°F (4°C) indefinitely, the minimum temperature at which
B. cereus can grow (Andersson et al., 1995). While O’Mahony et al. (2004) found that the majority of pouches after vacuum packaging had high levels of residual oxygen, this doesn’t imply that the
Clostridium species – which require the absence of oxygen to grow – aren’t a problem since the interior of the food often has an absence of oxygen. Most other food pathogens are able to grow with or without oxygen.