Baldwin Guide

[Trisha Quercioli]

Thisguide attempts to distill the science of sous vide cooking to provide you with the tools you needed to safely realize your creative visions. Part I discusses the techniques and safety concerns of sous vide cooking. Some prototypical recipes are explored in Part II. The mathematics of sous vide cooking are detailed in Appendix A. Finally, Appendix B discusses the specialized equipment used in sous vide cooking.

Sous vide is a method of cooking in vacuum sealed plastic pouches at relatively low temperatures for fairly long times. Sous vide differs from conventional cooking methods in two fundamental ways: (i) the raw food is vacuum sealed in heat-stable, food-grade plastic pouches and (ii) the food is cooked using precisely controlled heating.

Precise temperature control is important when you cook fish, meat, or poultry. Suppose you want to cook a thick-cut steak medium rare. You could cook it on a grill at over 1,000F (500C) until the center hits 120F (50C) and then hope the center will come up to 130F (55C) after a short rest. You might sear one side of the steak in a pan, flip the steak over, put it in a 275F (135C) oven, and pull it out just before the center comes up to 130F (55C). Or you could vacuum seal the steak, drop it in a 130F (55C) water bath for a few hours, pull it out of your water bath just before you want to serve it, and sear the outside in either a smoking hot pan or with a blowtorch; what you'll get is a medium-rare steak with a great crust that is the same doneness at the edge as it is at the center. Moreover, you can cook the flavorful flat iron steak (very safely) in a 130F (55C) water bath for 12 hours and it'll be both medium-rare and as tender as filet mignon.

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 122F (50C), but the common food pathogen Clostridium perfringens can grow at up to 126.1F (52.3C). So in sous vide cooking, you usually cook at 130F (54.4C) 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 130F (54.4C) 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 130F (54.4C) as it does at 140F (60C). What you are cooking is also important: at 140F (60C), 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:

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 want to learn more about food safety, please continue reading below; see my book Sous Vide for the Home Cook; the excellent free guide by Dr. Snyder; the FDA's food safety website; or your local health and human services department.

My goal is to maximizing taste and minimizing the risk from food pathogens. While pathogenic microorganisms can be controlled with acids, salts, and some spices, sous vide cooking relies heavily on temperature control (Rybka-Rodgers, 2001).

We can divide sous vide prepared foods into three categories: (i) raw or unpasteurized, (ii) pasteurized, and (iii) sterilized. Most people cook food to make it more palatable and to kill most the pathogenic microorganisms on or in it. Killing enough active, multiplying food pathogens to make your food safe is called pasteurization. Some bacteria are also able to formspores that are very resistant to heat and chemicals; heat the food to kill both the active microorganisms and the spores is called sterilization. [Sterilization is typically achieved by using a pressure cooker to heat the center of the food to 250F (121C) for 2.4 minutes (Snyder, 2006). To sterilize food sous vide, you'll need special retort plastic bags that can be used in a pressure cooker or an autoclave.]

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 130F (54.4C) 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 41F (5C) and 130F (54.4C) for less than 4 hours (FDA, 2009, 3-501.19.B).

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 130F (54.4C) 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.

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

In contrast, circulating water baths heat veryuniformly and typically have temperature swings ofless than 0.1F (0.05C). To prevent undercooking,it is very important that the pouches are completelysubmerged and are not tightly arranged or overlapping(Rybka-Rodgers, 1999). At higher cooking temperatures,the pouches often balloon (with water vapor)and must be held under water with a wire rackor some other constraint.

Seasoning can be a little tricky when cooking sousvide: while many herbs and spices act as expected,others are amplified and can easily overpower a dish.Additionally, aromatics (such as carrots, onions, celery,bell peppers, etc.) will not soften or flavor thedish as they do in conventional cooking methodsbecause the temperature is too low to soften thestarches and cell walls. Indeed, most vegetables requiremuch higher temperatures than meats and somust be cooked separately. Finally, raw garlic producesvery pronounced and unpleasant results andpowdered garlic (in very small quantities) should besubstituted.

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