nathanm

This might happen but I am pretty skeptical.

<span style='font-size:8pt;line-height:100%'>HOST'S NOTE: The main Sous Vide topic spawned this interesting discussion of cooling rates: since it was not directly related to Sous Vide and has info useful to chefs in many areas of cooking we have split it into its own discussion.</span> This is a common fallacy in thinking about heat transfer. Suppose you cook food for a period of time in a bath at temperture T1, then you move to a bath at T2, or the air in the room, or anything. The peak core temperature from the initial cooking at T1 will in general continue to rise for a bit after removing it from the bath - that is the rest time. If T2 < T1, i.e. you move it from a hot bath to a less hot bath, then after a while the core temperature will drop. HOWEVER, the peak value does NOT depend on T2. There is no difference between dropping it in liquid nitrogen, or putting it in a bath that 1 degree below T1. As long as T2 < T1. This fallacy usually presents itself in the form of saying "plunge the food into ice water to stop the cooking". Nope, doesn't work. Plunging it in ice water will chill the food quickly but it will reach the same peak temperature. The reason this is true is that the speed with which heat diffuses through food (or any solid) is fixed by the material. When you put the food in a colder bath, it starts to draw heat out of the food into the bath, but it can't speed up and overtake the heat you were putting into the food earlier. Loosely speaking the "heat wave" that you push through the food while cooking cannot be overtaken by the "cold wave" from chilling because they travel at the same speed. Our instinctive notion is that if it is really cold then it will somehow travel faster. This is like thinking that a heavier object will fall faster. Well, as Galileo showed all objects fall at the same speed. And all heat travels at the same speed. If T2 > T1, then peak caused by the initial cooking at T1 will still peak the same time, but then after that it will rise due to additional heat from T2.

Just New Delhi and Agra on this trip. I forgot to say that Agra recommendations wolud be good too...

Thanks! I think I ate there many years ago - it is mughal style food, right? I think I am staying at Taj Palace hotel.

I made the reservations in April / May for October.

I will be in Tokyo for a short business trip and want some reccomendations for the best places to eat - particularly high end Japanese food - either traditional, or modern. I have resevations at Arionia de Takazawa already. Where else should I eat?

I will be in Seoul in Ocotber and would like to find some great places to eat. I am mainly interested in high end dining, but would also stop for street food or similar if it is really good. Is there anybody doing modernist food (i.e. analogous to Ferran Adria / Heston Blumenthal) in Korea?

I will be on a business trip in Singapore and want to sample the cuisine. I am mainly interested in high end restaurants, but I would like to try some of the best of the street food also. I am trying to buy the Maknasutra book. What is there on the high end dining scene? Will the book cover that, or is it mainly street food?

I will be spending a few days in Beijing and Shanghai this fall, and would like some restaurant recommendations. I am interested in high end cuisine - both traditional and "modernist" food. If there are Chinese chefs experimenting the way Heston Blumenthal or Ferran Adria do then I would like to find them. I am interested in Chinese food however, not a purely western restaurant. In Beijiing I have been told that Made in China has the best Peking Duck (despite being in a western hotel). South Silk Road, and a place called Tianda Yia Jia have also been recommended. I have no recommendatinos for Shanghai yet.

I will be going to New Delhi this fall for a couple days and want some recommendations for great food. I am interested in both traditional Indian food, as well as more modern interpertations - if there is anybody who is cooking in India like Heston Blumenthal / Ferran Adria, I would be interested in trying it. I love all Indian food - south and north. I would like to have some great Masala Dosa while there, but also open to anything else.

There is NO point to multi-stage cooling. If you are going to store the SV product after cooking, then you should cool it to storage temp (very cold - ideally just above freezing) as soon as possible. The best way to do this is to either immerse in ice water, or use a blast freezer (like a convection oven, but with cold air not hot). The point about chilling before vacuum packing is that the boiling point of water drops with pressure. If you try to vacuum pack hot broth, it will boil over - if cold it may still boil over but can take more vacuum before it does. However, for most meat, vegetables etc, this is pointless. Some people think that the amount of vacuum matters (the last point) but there is little evidence for this for most food. Some very delicate foods can get crushed by full vacuum, but the idea of calibrating the vacuum pressure to each type of food is not at all required.

Yes this is exactly it. The only reason to have it rest is if you use a cooking bath temp that is much hotter than the final temp. Then you need to remove it and let it rest to allow the core temp to come up. But frankly this is a silly way to cook in most cases.

I have done similar charts - it is amazing how close one can get....the mathematical model matches reality very well indeed.

Yes, heat diffusion is the slow part. Roughly speaking you can expect diffusion to scale with time like the square of the thickness, so a steak that is twice as thick should take 4 times longer to cook.

I think you'll get the best results from browning on the stove, grill, griddle, torch etc. While you can program ovens like CVAP to get browning right, it is tricky. It is a bit easier with a Rational combi-oven. However you'll get the most control if you brown as a separate step (either before or after the cooking and holding).

Monitoring is pretty easy - use a digital oven thermometer like this. Most of them have a thin wire between the probe and the display unit, and you can just close the oven door on the wire and it works fine. I use a USB thermocouple interface and display the result on PC, which can then show you how the steady the temperature is, make graphs etc. But that is overkill for most people. It is much harder to control the temperature (as opposed to just monitoring it). A PID controller could in principle be adapted to the oven, but that may not be easy.

Winston C-Vap is one of a whole set of cook-and-hold ovens. Alto Shaam is likely the market share leader - it's cook and hold ovens are all over the place, but they are not that high tech in terms of temperature or humidity control - it is basically a low heat oven with humidity. Winston is a bit higher tech, but similar. The most technologically interesting one to me is Accutemp. Their ovens pull a vacuum to lower the boiling point of water - so they literally are low-temp steamers. Sort of the opposite of a pressure cooker. This ought to give you faster heat transfer and have some other effects, but I am not sure how noticeable this is. All of these units are similar to a simple version of a combi oven - it is not as powerful or does as many modes or types of cooking as a combi-oven. However, for low temperature steaming or high-humidity low-temperature baking/roasting they can be very good. The temperature control in all of these ovens is something to watch - they can have inaccurate thermostats.

Jack, you should try some experiments with pasta to see what happens! Spoilage bacteria are typically aerobic, so vacuum packing will retard them. That is part of the reason to vacuum pack in sous vide. Pre-cooking at 55C for >1 hour should kill essentially all spoilage bacteria, and thus improve the keeping aspect even further. I am not sure whether it would be big difference from simply vacuum packing, but perhaps it would. It is worth trying. The pre-cooking will not kill anaerobic spores, so keep the pasta very cold and don't keep too long (but 5 days should be fine, and longer if you keep near 1C - I put the FDA standards is a previous post). As per the post above the pre-cooking may partially gelatinize starch in the pasta but I am not sure that this is bad, or that you'll be able to tell after the final cooking. Gelatinization is a key part of cooking pasta, and since you will ultimately gelatinize it in the final cooking, it may not matter if some gelatinization occurs early. My guess is that you may need to cook the pasta less in the final cooking.

I forgot to add that the second cooking would like the bacteria - but the problem with C. perfringens is that it makes a toxin (actually more than one kind depending on the strain), and it takes lots of cooking to destroy the toxin. This, by the way, is the same pathogen that causes gas gangrene, and a diease called pig-bel, as well as two different types of toxin. It is not a friendly bug.

The problem is that C. perfringens can grow very fast under some circumstances - with doubling time of 7.5 min at 37C. This depends on the strain and so forth, but unless you really know. Worse, the spores are activated by preheating to 70C. So, this case MIGHT be one where you a lot more than 10X. To know for sure you'd have to know the strain, the pH and various other conditions. If the meat had cooled down to 120F/48C, then I would say go ahead. But the final temp was right in the maximum reproduction range, and we don't know how long it was there. Bottom line is that it is far safer to throw them out.

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. ← The risk of Clostridium perfringens is too high - throw them out. Of course I don't know that your duck was contaminated by C. perfringens, so there is a chance you'd be OK, but why take a chance of getting really sick?

I'm still coming on the thread. I too want a signed copy of my book! Alas it is not done yet. We are working on it, but like a tough piece of meat it is going to require a long cooking time to make it consumable. I do not think very highly of the Ghazala book. Yes, it is a Fluke thermometer. However I also like Extech. My favorite one (posted up thread) takes two probes so you can monitor two temperatures at once.

A combi oven inevitably has temperture fluctuations of a couple degrees. Gas units are much worse than electric in this regard. At very low temp, putting water in the pan helps even out temperature fluctuations. Above 60C/140F, the fluctuation matters less, so I usually don't do it. Always use steam mode when cooking sous vide in a Rational or other combi oven. Nathan

At low temperture energy usage really should not be an issue. It may sound strange, but it is often easier to get accurate temperature holding with less insulation because when the heater stops it cools down faster. So, if there is a small overshoot, it gets corrected faster. At higher temp, insulation is more of an issue but is still small compared to evaporation. The main way you lose energy from a water bath is evaporative cooling. Covering the water bath - either with a hard cover, or plastic film (at low temp) or aluminum foil, is the most important thing you can do to save energy. It also prevents your bags of food from becoming high and dry and thus not heated. Or your temperature sensor can be high and dry which will cause overheating. Most lab water baths have an automatic shut off feature if water level drops too low, and this can have a bad effect. Evaporating 1 liter of water (1 kg) takes 2,260,000 joules of energy. A watt is 1 joule/second. So evaporating 1 liter of water over the course of an hour takes 628 watts. Evaporation occurs whenever the air above the water is less than 100% relative humidity. Covering the water bath effectively keeps the humidity at 100% right above the water, and shuts evaporation off. The more water surface area that is exposed to the air, the more evaporation you will get. So, a wide shallow pan will lose more heat this way than a tall deep pan.

This states the situation very well. The main variation between water baths is wattage, water movement and PID control. To plug into a standard US electrical circuit, all of the devices discussed are 1800 watts or below. You get faster heat up with 208/220/250 volt, but most water baths do not feature this (but you can build or buy them that do). Commercial laboratory water baths have components chosen to do the job well. You can approximate those results with re-purposed components like Auber instruments controller, rice cookers, steam tables and so forth. The main issues that you need to watch are getting PID parameters adjusted properly (or use automatic tuning PID), and making sure that the water is stirred. If it is all set up properly there is no difference in functionality between this and a commercial water bath. On the other hand, if you don't stir the water you could get temperture stratification. If the temperure sensor is sensing unstirred water it will do the wrong thing. If the PID parameters are set wrong it won't control well. These are all simple to solve.