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Sep 5, 2012 11:23 AM

Food temperatures are more then you need

I have been interested in sous vide and low temperature cooking lately. However I have been a bit wary of some of the temperatures they cook at as far as food safety goes. One example is Heston Blumenthal's roast chicken. He does it low and slow until the internal temperature reaches 140F. However current FDA recommendations say it should be cooked to 165F. As much as I want my food to taste good I also want to be safe. So I did some research. I found this PDF which summarizes things pretty well.

It turns that it's not just temperature but also time. The standard for chicken is a 7D reduction in bacteria. This basically means the bacteria population is reduced by 99.99999% of the original population. At 165F this is attained instantaneously which is the reason the FDA chooses that temp. However the same standard can be reached by holding it at lower temperatures for a longer amount of time. According to one of the charts on the PDF you can attain this at 140F by holding it there for ~35 minutes. Since Heston cooks this for several hours, he easily meets the time requirement and the chicken is more then safe without drying out the meat. At higher temperature you can shorten the time and you can even go as low as 135F and still kill bacteria although it might be a little too rare for some people. This also means that items that are cooked sous vide for 24 hours easily meet this time requirement as well.

So my argument is that while it's better to be safe then sorry, you should also be rational in your fears. To me cooking at 165F is like walking with a helmet on. You are definitely safer with the helmet but you are also perfectly fine without it. Am I wrong in my thinking?

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  1. All good safety protocols have a margin for error. The smaller the margin, the greater the chance of a bad outcome. The USDA-FSIS recommendation are intended to ensure safety, since that is the mission of the Food Safety Information Service.

    You should take note that a recent thread discusses an incident of food poisoning from chicken cooked sous vide.

    2 Replies
    1. re: GH1618

      I think the 7D standard takes the margin of error into account. 3D kills 99.9% of bacteria and is probably perfectly safe. 7D is 5 standard deviations above that. I am not advocating anything less then that. Holding the chicken at an internal temp of 140f for at least 35 minutes will give the same bacteria death as chicken that has attained 165f for just a few seconds. The FDA recommendation make it seem like anything under 165f will have bacteria without specifying time. That being said this isn't my recipe but Heston Blumenthal, a 3 star chef. Do you think he would be so irresponsible to recommend something so dangerous?

      1. re: Captainspirou

        "The FDA recommendation make it seem like anything under 165f will have bacteria without specifying time."
        Actually, the FDA code does specify time. 15 seconds at that temperature, or the time/temp combination in the charts under 3-401.11

    2. By the way, you are misinterpreting the cooking time as the pasteurization time. If the pasteurization time is 30 minutes at 140 °F, this means that every part of the food is at 140 or more for 30 minutes. The time required for every part of a piece of meat to reach that temperature after being immersed in preheated water will depend on its thickness.

      7 Replies
      1. re: GH1618

        I have done no such thing. I think you are misinterpreting what I am saying. I did not say that you should cook the chicken with an oven temperature of 140f for 30 min. I made it clear that 140f was an internal temperature.

        1. re: Captainspirou

          What you wrote was: "Heston (Blumenthal) cooks this for several hours," appearing to compare it to the 35 minutes required at 140 °F for safety. If you did not intend that as a direct comparison, then at least you were not making yourself clear.

          1. re: GH1618

            I also wrote "He does it low and slow until the INTERNAL temperature reaches 140F. However current FDA recommendations say it should be cooked to 165F." I excluded the word 'internal' from the rest of my post because I thought it would be redundant but apparently I need to do it so people don't miss the point.

            1. re: Captainspirou

              You are still not clear about the "several hours." What is it that is cooked for several hours, what are its dimensions, and how long is the entire thing at 140 °F? When you wrote "until the internal temperature reaches 140," it seems like he stops cooking there, which would be wrong.

              1. re: GH1618

                With Sous vide it is wrong to say that the item is cooked till its internal temperature is 140deg. Rather it is cooked in a 140 deg water bath till the temperature of the food matches the water, and then it is held at that temperature for a while longer. 30 minutes may be long enough to kill enough bacteria. But some meats are held at the target temperature long enough to break down collagen. Since doneness (i.e. contraction of the meat fibers) is a function of temperature, not time, meat can be held at the target temperature without being over cooked.

                1. re: paulj

                  I see. But the question is, how is it known (the food being sealed) when the food is uniformly heated to the water temperature? In a commercial kitchen, the process can be calibrated and controlled for reproducibility. In a home kitchen, there is likely to be more variation in portion size and initial temperature, both of which will affect the cooking time.

                  1. re: GH1618

                    Sous vide pasteurization charts account for both factors and include a margin of error. The bigger problem in a home kitchen is miscalibrated equipment and technique missteps.

                    Take a look at Baldwin's charts.

      2. Sous vide is a fairly established technique, and it's as safe as any other cooking technique when done correctly. The USDA guidelines are quite simplistic and aren't designed to apply to sous vide cooking. Sous vide does have its own specific technique pitfalls, and some research (as you seem to have done) is advisable before starting to use the technique for this reason.

        The Blumenthal roast chicken is an interesting case study in non-sous vide low temp cooking. It relies on the same principles of pasteurization as sous vide does, effectively killing germs with a lower-than-normal temperature by holding the chicken at that temperature for a longer time. But notice that unlike sous vide, the cooking medium - the air in the oven in this case - is not the same temperature as the desired final temperature of the meat. The reason for this is that cooking immersed in water quickly brings the surface of the meat to the temperature of the cooking medium, while cooking in air actually ensures that the surface of the meat is cooler than the surrounding air. The main reason for this is evaporative cooling. This means that though 140 can be a safe temperature for chicken if it is held at that temp for long enough, you can't safely cook chicken at 140 in a normal oven. Add enough humidity/water vapor to the equation (as you would in with a much-more-expensive combi oven), and you put a stop to evaporative cooling and also increase the rate of heat transfer to the chicken and 140 can again be a safe cooking temperature just like it can be when cooking sous vide.

        The take home point is that if you want to cook at or to a low temperature, it can certainly be done safely but some research is advisable.

        4 Replies
        1. re: cowboyardee

          My main point in post was about internal temperatures and bacteria associated with it. Not so much the methods used to reach it.

          That being said, It won't cool forever either. There's only so much water a piece of meat can hold and it will eventually rise. Evaporative cooling is a much bigger factors for higher temperatures where evaporation occurs at a much higher rate. Not only that but temperature equilibrium means it will always reach the ambient temperature given enough time. Chicken that is roasted at 400F will reach 400F if you leave it there long enough. It's just it will be ash by then. This video goes over the recipe I am talking about.

          While my original post was referring more to his chicken cooked in a 195F oven, this one is cooked at 60C which is 140F for 4 hours. He takes a few extra precautions to account for the dangers you mention by boiling the chicken for 30 seconds and then dunking it in ice water.

          Thanks for the Douglas Baldwin link. It's very informative.

          1. re: Captainspirou

            You misunderstand. Yes, eventually chicken dry roasted at 140 or 130 will reach those temperatures, having given up their moisture. It will take a looonnnng time, btw. But the problem is what happened in the meantime. When the surface of the chicken stays below about 125 over the course of 4 hours or more, the temperature is actually ideal for the growth of many bacteria. And though most of those bacteria are eventually killed when evaporative cooling slows down and the surface heats up, you've given some bacteria a chance to produce heat-stable toxins that can also make you sick. Staph aureus is the most well known of these endotoxin-producers.

            The above only describes the case where no extra precautions are taken. In the case of the youtube video, the dunk in boiling water before cooking is a good and useful safety measure, but it's needed because the oven temperature is really at the absolute bottom end of the safe range, even though pasteurization can be achieved 10 degrees lower. And even with that precaution in place, that method still takes something of a calculated risk that cooking in a slightly hotter oven does not. Not a huge risk, but a risk nonetheless. Better be sure the oven isn't even a little bit miscalibrated (as most are).

            I am a proponent and frequent user of sous vide, and a big fan of Blumenthal - I'm not trying to steer people away from low temp cooking. But I urge people not to fall into the same trap as those who insist low temp cooking is unsafe in the home. Don't just memorize a few basic figures and guidelines and apply those to everything. Low temp cooking demands a more nuanced understanding of food safety. Either that or following recipes closely and hoping that those recipe writers have done their homework.

            1. re: Captainspirou

              I've often thought about this issue, and I agree with you totally. I never cook any meat to 165...If you do it's shoe leather. I usually cook chicken until it's just not red on the inside, no more than that and it remains juicy and flavorful. That said, I would not be suprised if cooking sous vide for several hours to 140 is safer than my more traditional fast cooking methods.


              1. re: Burghfeeder

                I think "several hours to 140" is for roast chicken. That's not sous vide, which means "under vacuum."

          2. I didn't know this - thanks for posting it. But for me, marginal improvements in the taste and texture of what I eat aren't worth the risk of landing in hospital. Better safe than sick.

            1. Bacteria activity is a function of time and temperature which addresses the food safety aspects of cooking, but how does time and temperature effect tenderness of tougher cuts?

              For example, would you sous vide a brisket? Would the collagen break down to provide an unctuous bite of food? Or is sous vide only suited for tender cuts of meat?

              4 Replies
              1. re: dave_c

                Sous vide really shines with tough cuts of meat. Collagen breaks down into gelatin (which is what makes braised and bbq'd meats tender) starting at least at 130 - probably a bit lower, but you can't pasteurize below that. The conversion just takes longer than it does at higher temperatures such as those where you traditionally braise. But you can hold food in a sous vide bath for a very long time, effectively breaking down the connective tissue in the meat without shortening the meat's fibers and pushing out its natural juices. The result is meat that's both as tender as you care to make it and extraordinarily juicy.

                This is why you can find so many recipes for sous vide short ribs and the like. You can also do sous vide brisket, but typically you'd break it down into smaller (less thick) pieces before cooking for the sake of safety and efficiency.

                Incidentally, sous vide isn't limited to cooking below 150 degrees. You can use the technique to cook at any temperature 212 and below, though some of the bags themselves are limited to the sub 180 range.

                1. re: cowboyardee

                  There might even be a way to do it at a higher temp with oil instead of water.

                  1. re: Captainspirou

                    However there is water in most food. The bubbling and sizzling you see when food is fried comes from water escaping the food and turning to steam. Some sources claim that as long as there is bubbling, the food can't absorb oil because of this escaping steam. It's after the bubbling is done, and during cooling, that the food absorbs oil.

                    Duck confit and carnitas are poached in fat, though the fat temperature is kept below (water) boiling.

                    Other than the 2 state french fry method, I can't think of recipes that use oil between 212F and 350F.

                    1. re: paulj

                      Frying chicken for one.

                      But that being said there is no food anyone would eat with an internal temperature above 212F so doing sous vide with oil would be useless. It's just in theory it can be done at higher temperatures.