DouglasBaldwin

Assuming the duck legs were heated through to 180F (82C) before the heater shut off, then all the common food pathogens would have been destroyed. The problem, is that the temperature is not sufficient to destroy the spores of clostridium botulinum (type A,B) or the spores of clostridium perfringens. If either of these spores started growing and multiplying, they would not cause any obvious signs of spoilage. However, heating the meat through to 180F (82C) and holding it at that temperature for at least 10 minutes will inactivate the c. botulinum neurotoxins. Moreover, the spores of c. perfringens need about 15 hours below 130F (55C). So, finishing your cooking is probably okay, but it is outside FDA guidelines.

Well I ran out and got a kilowatt meter this morning, and found that when set at 141F that the Auber PID controlled steam table averaged about 60 watts once up to temperature (to be precise, it used 0.07 kW-h in 1:15). I'm not surprised by this (rather) low power usage because the outside of the food warmer is never uncomfortable to the touch. [Edit: To go along with NathanM's excellent post below, I thought I should mention that the steam table was covered with a metal lid to minimize evaporation. Also, measuring over 4 hours, it turned out to consume 69 watts.]

Using an uncirculated steam table and an Auber PID, I found that the spacial uniformity of the water was ±0.6°F (±0.3°C). That is, using a Thermoworks MicroTherma 2T, I found that the difference between the hottest and coldest spots in the water bath was 1.2°F (0.7°C). To test the spacial uniformity, I first let the water bath come up to temperature, then moved the probe all around the water bath and recorded the max/min temperatures. I then added three frozen chicken breasts, and repeated this measurement every 15 minutes. The average spacial uniformity was ±0.6°F (±0.3°C), the max was ±0.8°F (±0.4°C), and the min was ±0.4°F (±0.2°C). While it may not be necessary, I still feel circulation is important because it will cause the surface temperature of the meat to come up to temperature much faster.

Up thread, pounce mentioned using a counter top food warmer/steam table with a PID. When using a swamp cooler water pump to circulate the water, he said it worked just as well as an immersion circulator. If a water pump (or air bubbler) is not necessary in a rice cooker, it may not be necessary in for a counter top food warmer either. Since I have an Auber PID and a food warmer, I will experiment with them this coming week and report back.

For a good discussion on why time is important, see NathanM's post #181. You can also see my sous vide web guide which goes into quite a bit of detail here. Basically, there are two time scales in sous vide: how long it takes to come up to temperature and how long it takes to dissolve the collagen into gelatin. The first strongly depends on the thickness of the meat, and can be approximately calculated using either NathanM's or my own tables. The long cooking times (8-48 hours) must be at or above 131F (55C) for food safety reasons (so no fish or rare meats); the long cooking times are only appropriate for tough meats, because a tender cut of meat would turn to mush.

You are probably being overly cautious. Reynolds Handi-Vac bags were discussed at some length up thread, see posts: 1046-1048 and 1055-1060. I use them when I'm at my parents house (where they use a slow cooker with a Ranco ETC and air bubbler) and I cannot smell or taste the plastic bags.

You are most welcome. I calculated the cooking times for frozen meat last night, but it meant solving a nonlinear heat equation that is numerically "stiff" (that is, very difficult to calculate). I only have a thermapen and so have not been able to test the accuracy of my calculations. Indeed, all my calculations are based on the thermal conductivity and specific heats I found in journal articles and not my own experiments. If any of you have the equipment necessary to check my calculations for frozen meats, I would really appreciate. Thanks, Douglas

After reading through this amazing thread, I thought I might try and summarize the information into a brief guide for new (and old) users. The first draft is linked below: http://www.douglasbaldwin.com/sous-vide.html It is of course woefully incomplete, but I will continue to work on it in the coming weeks/months. Any suggestions for improving the guide would be greatly appreciated.

Since I always set my water bath at just above my desired core temperature, I put just those times in a convenient PDF for myself. I uploaded it here if you would like to download it.

Thanks for the replies. I guess I'll stick to the amazingly delicious 24 hour/131F (55C) flat iron steaks, and not tempt getting sick from c. perfringens (or bacillus cereus or staphylococcus aureus, whose growth ranges apparently both go up to 122F {50C}). Just to be clear, the opinion is that Blumenthal's steak recipe is questionable from a safety stand point and not that doing it SV is inherently more dangerous.

I have a question about cooking steaks/roasts at temperatures lower than 131F (55C) for long times. I am thinking about Heston Blumenthal steak recipe, where he sears the outside of a roast and then heats it too 122F (50C) and holds it there for 18 hours. (Is this to allow the cathepsins enzymes plenty of time to tenderize the meat?) Anyway, I would like to try this sous-vide (with a single steak), but don't want to get food poisoning either. If I understand correctly, the main concern with steaks and roasts is surface pathogens. Since I always sear after cooking, I have been very careful to make sure I either cook the steak for less than 4 hours or at 131F for longer times (e.g., 12-24 hours for flat iron steaks {as per nathanm's suggestion in posts #203 & #675}). I am very leery however of cooking a steak in a 122F (50C) water bath for 18 hours, since that is well within the growth range of clostridium perfringens (which grows between 59F-127.5F {15C-52.3C}). In post #897, nathanm said even after searing it (officially) shouldn't be held at 125F for more than 4 hours (and then said unoffically that searing first and doing 8 hours at 125F would probably be fine). Do you think it would be safe to: drop a frozen (vacuum sealed) steak into a pot of boiling water for 30 seconds, then put it into an ice water bath (for a minute or two), and then into the 122F (50C) water bath for 18 hours? That is, would dropping the frozen steak into boiling water for 30 seconds be sufficient to destroy the surface pathogens? And, is 122F (50C) for 18 hours asking for trouble? Thanks, Douglas

Hey Mike, I know it has been mentioned up thread, but I would highly recommend using an aquarium air pump to circulate the water. I noticed substantial differences in temperature at different locations in my slow cooker before I add the bubbler. Just put the tubing into the slow cooker (no air stone required) with a little weight to keep it on the bottom and you will be good to go. I now use an immersion circulator, but find that the results are no better than my previous slow cooker, air pump, PID system. Best Wishes Douglas

Just as an update, I am now not recommending using an "airstone" with the air pump. When I did some pulled pork butt over night, my kitchen had a strange chemical smell in the morning which I was able to determine was from the airstone. Instead, I recommend just using the air hose and clamping it to a weight in the bottom of the crockpot; I checked and it is still sufficient to circulate the water.

It is just a little 4" airstone, and I basically just threw it in the pot. The air pump is for a 20 gallon tank and seems to agitate the water enough that I don't think it would matter where I put it in the pot. I don't think the airstone is actually necessary -- anything that would keep the end of the air tube/hose from floating to the top should be sufficient. I thought about putting a 'rack' on the bottom, but (with the exception of eggs) nothing has just sat on the bottom so I didn't feel it is worth the effort. Anyway, below is my crockpot setup. The blue thing is the airstone, the gray wire is the temperature sensor. The lid then sets on top, but I took it off for the picture.

You could also just trying calling some of the smaller meat lockers in your area (say, search Google maps for "category: Meat Packers"). Often they are very friendly and will likely know a farmer who raises what you want (and how you want it). We found our beef supplier through word of mouth (and get the calf of the same cow every year). But when a friend wanted a whole lamb, I gave the locker (where we hang our beef at) a call and they found just what my friend needed. At least with beef, it will likely be a substantial wait for your meat once you find a farmer who raises what you want. When we switched farmers, it took a good 4-5 months to get our side of beef -- a couple months to get the animal to market weight (1300 lbs on the hoof) and 28-days of dry-aging. The price is based on the weight "on the hoof" and that days market price (plus a packaging fee). All told, I think it came out to be around $2-3/lbs (for the packaged meat).

Hello All, I just started reading about sous vide last week and find it fascinating. As an experiment (until the immersion circulator I won on eBay arrives), I have set up a 6-quart crock-pot (on low heat) with a PID controller and let it stabilize at 141°F. I then put in a single thawed (vacuum packed) chicken breast. The temperature reading on the PID stayed nice and steady the whole time. After one hour I checked the water temperature with my favorite thermapen, and found that the temperature ranged from 136°F to 141°F. The 141°F, of course, was at the temperature probe of the PID (on the bottom of the crockpot) and the 136°F was near the surface in the center of the pot. At least in my crockpot, the food seemed to really hamper the normal convection currents in the pot. Before I put in any food, the water temperature varied by less than 1°F when I measured it at various points with my thermapen. I am now cooking a pork chop at 141°F with an aquarium bubbler (air pump $15, tube and "airstone" $4). After about an hour, I measured the temperature at various points in the pot with my termapen and found there was no more than 1°F difference between the hottest and coldest points.