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nathanm

Water Baths and Immersion Circulators

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Technology in the kitchen seems to evolve fairly slowly - most of the equipment we use hasn't changed in generations. One new area that has been quite exciting is the use of laboratory equipment in the kitchen. Chemical and biological laboratories follow "recipes" with even more precision that chefs do, and as a result they have some equipment that is very worthwhile in the kitchen.

One example is laboratory water baths - a very precise sort of bain marie. These have become widely used by cutting edge chefs such as Ferran Adria of El Bulli, Heston Blumenthal of The Fat Duck, and Wylie Dufresne of WD 50.

The water bath is just what it says - a thermostatically controlled bath of water in which you can immerse things to cook them. Typically they hold the temperature very accurately - to a small fraction of a degree. To cook with a water bath you must immerse the food in the bath - typically this is done by sealing the food in a vacuum packed bag (sous vide), although you can also place a pot or bowl in the water, much like a bain marie or double boiler.

This post is intended to be a chef's guide to the various sorts of water baths, and where to buy them.

There are several types of laboratory water bath that are relevant. Here is a manufacturer's web page that shows several varieties. Here is a different style

The first style is typically called an "immersion circulator" - it is a precise heating element, thermostat and pump. It is meant to be suspended in a tank or pot - generally by clamping to the side. The pump keeps the water circulating, much as the fan in a convection oven.

The good news about immersion circulators is that they are very versatile - you can use them with any deep container that holds water - a large stock pot or tank. Most kitchens have deep hotel pans or other containers that could be used.

The bad news about immersion circulators is that when you stick the unit onto the pot or tank, it is very difficult to cover the tank and ensure a good seal. This means that the water will be subject to a lot of evaporation. For some uses - keeping food warm, or quickly poaching fish, this is fine. For other uses - like doing confit in sous vide where the cooking time is 7 to 10 hours, it is a real problem. When the water level drops to a certain point the unit will turn off, leaving your food to come to room temperature, and probably to spoil. I ruined a batch of short ribs this way once.

One way to combat the evaporation is to use floating balls on the top of the water - such as a bunch of ping-pong balls. Lab supply places like CP, Fisher, VWR sell special ones, but ping pong balls work. However, it is much easier to use a water bath with a tank cover.

The second type of water bath is better for general purpose use – it is basically an immersion circulator that comes with a built in tank and cover. These are called "water baths", "circulating water baths", or something similar.

One variety only heats the water. Another variety is able to do both heat and cooling so you can keep the water at a temperature lower than the kitchen temperature. Those units are much heavier and more expensive, and for the moment there is much less call for chilled water bath than a hot water bath in the kitchen. So, I’ll restrict my comments to the heated ones.

Circulating water baths of this sort typically have inlet and outlet port which allow them to pump water through tubing to other scientific equipment. For kitchen use you will want to use a loop of tubing to connect the input to the output.

If you want a water bath for cooking, you probably want a circulating water bath – it is like a convention oven in that the pump causes the water to circulate and thus prevents cold spots. There are some less expensive units, usually called utility water baths that don’t circulate – I do not use them much myself. The only advantage they have is if you wanted to cook right in the unit, because they are easy to clean.

Some people report using home appliance slow cookers, or crock pots, as water baths. They are cheap, but they have several problems. First, they don't have accurate temperature control - usually it is "high" and "low" and neither one is calibrated properly. Second, they don't circulate the water. I do not recommend them.

There are other kinds of laboratory water baths – for example orbital or shaking water baths. These have a cage assembly inside the water tank, which shakes or vibrates via a motor in order to gently agitate containers placed in the cage. This is very important for some kinds of biological work, but it is not required for cooking, and is usually much more expensive.

All water baths and circulators come in either analog or digital form. The digital versions are generally easier to set and read, but either one will work.

There are dozens of manufacturers of water baths. To add to the confusion, there are also lots of companies that sell other people’s water baths under their own name.

The three largest scientific equipment companies are Fisher Scientific, http://www.vwr.com/index.htm ]VWR International and Cole Palmer. Each of them sell several brands of water baths, including one or more product lines under their own brand name. Note that they do not actually manufacture the baths, but it certainly can look that way because of the private label branding.

These supply houses sell to scientific labs – such as pharmaceutical companies or government research labs. As a result they are NOT cheap – this is a market where the customers are not very price sensitive. The units are generally $800 to $1500 depending on the size for a circulating water bath or immersion circulator. High end units can be $4000 or more. These are almost always well made and sturdy, but it comes at a price, especially if you buy them new.

The other way to buy is second hand. Because these units are built to high standards for scientific purposes, they generally last a long time. The two main sources there - used from dealers in used lab equipment, or on eBay.

Water baths are so commonly used in labs that there are literally hundreds of them for sale from used equipment dealers. Here is one example site. Models that are suitable for chefs generally go for $250 to $350. eBay generally has plenty of them also, several dozen at any point in time. The price on eBay is highly variable. Some of the sellers hold out for a lot, others don’t. I recently bought one very nice 20 liter water bath for $150. Two days later a second unit of the identical model went for $220.

To find them on eBay, the best method is to go to “see all eBay categories”, then “Business and Industrial”, then “Healthcare, Lab & Life Science”, then search for water*, bath, or circ* .

Using a water bath is pretty simple – set the thermostat at the right temperature and turn it on. That is the basic set up, but there are some other details. Most digital models allow you to switch between Fahrenheit and Celsius temperature scales. In addition, there is usually an over-temperature cut off which turns the unit off if some for reason it gets past a certain temperature. On some models things like how to switch between F and C is not obvious – then you need a user’s manual. Many of the better manufacturers, like Lauda have PDF versions of their manuals on line, even for discontinued models.

If your water is very mineralized, you may get deposits on the heating element. These can be cleaned as for any sort of heating element in water. Or, you can use softened water.

The size water bath you need depends on what you are going to cook. In general, a 10 liter model is the smallest you want to use – although I have a couple 7 liter ones that I use for small batch experiments. 20 liters is better. Sometimes you can find even larger ones, but the problem then becomes the fact that the wattage may not be enough to handle that much water.

Most of these units are relatively low wattage – 1000 watts to 2000 watts. This means that it takes a while for them to come up to temperature – often 20 to 30 minutes. The larger the water tank size, the longer it will take to heat up. However, by the same token the larger the tank, the less the temperature will drop when the food goes in.

If you get a used unit you will need to clean it very thoroughly before using it. You may need to use a water scale remover on the heating element. Replace any tubing with new rubber or plastic tubing rated to take the temperature you will use.

I generally leave the water in the water bath between uses - the tanks are stainless steel, and everything seems to be fine with that. Periodically it should be emptied - and always emptied if food particles spill into the water.

Note that in all cases you are cooking with the water as a means to heat the food, but the food is not directly in the water - it is sealed in a plastic vacuum bag, or it is inside a container . In principle, you could poach directly in the water, but in that case case you would need to clean the unit very carefully afterward, because food particles could get stuck in the pump. "Utility" water baths, mentioned above, that do not have a circulation pump are easy to clean, so they could be used that way.

Most water baths are designed to go from room temperature up to 100C / 212F. A few of them have the ability to go higher if you use oil in them, however, they are not designed for use as a deep fryer – they are intended for various synthetic oils.

That should serve as a basic primer to water baths themselves. Their use in cooking depends on what you are after, of course. The sous vide thread (elsewhere on eGullet) discusses that form of cooking. Water baths with sous vide are a great way to cook.

Convention steam ovens, such as Rational, can also be used instead of a water bath for sous vide or other cooking. However, water baths have the advantage that they are generally much smaller, and cheaper. I use Rational ovens when I am doing something big, but for a small quantity, or when I want to cook something for long periods of time (like up to 36 hours for some things), it is difficult to tie up the Rational. A water bath is much more practical in that context. The temperature control is also more accurate.

You can also use water baths to keep things warm. Any deep stainless steel container can be immersed with the bottom in a water bath – much like in a steam table, but with more accurate temperature control. This lets you keep things warm without sealing in a vacuum bag. As another example, when I make a warm foam, such as warm potato foam, with the ISI foamer, I fill the units then leave them in the water bath at 140F / 60C.

This may be more than you ever wanted to know about water baths, but hopefully somebody will find it interesting.

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Nathan, did you say that the temperature control on a water bath is more accurate than on a Rational steam oven? If so, can you explain why? I was under the (mis)impression that the steam oven provides the most accurate and precise temperature control for sous vide cookery.

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Good article.

You might make the point that watre baths with sous vide are the preferred cooking method for long-time low temperature cooking - typically 45C for fish and 58C for meat. Hard to get this by any othre method, and in particular steam ovens tend to be too hot

My favorite and local manufacturer is

http://www.grantlaboratory.com/product_select.html

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Rational ovens are great - I have two of them. I love them and if I had to choose between them and water baths, I would keep them. But I don't have to choose, so I have both!

There is inevitably a bit of variation in the temperature of any oven. I have calibrated mine and as the heating element turns off and on to maintain temperature there are variations of plus or minus 2 degrees at least, and on some ovens as much as 5 degrees. Gas versions are worse than electric.

This is a cyclic variation - it cycles around the set point. The average temperature is correct, but over a few minute time scale it varies.

At the high end of the oven range this is not bad, because if your are at 400F, then there really is not much difference between 395 and 405.

However, if you are cooking salmon mi cuit and want it retain the raw look, then you must cook at 104F. In that case plus or minus a couple of degrees is a much bigger problem. Or for cooking red meat sous vide (beef tenderloin, rack of lamb), you want to know the temp pretty accurately so that know whether you are doing rare, medium rare. I generally do rare at 125F, medium rare at 130F. With a water bath I really know what the temperature is.

Also, note that the Rational does maintain the right temperature ON AVERAGE. For a large piece of meat that variation does not matter, because a big piece of meat (or other food) takes a long time to cook and small variations do not matter much. So, when I cook a big beef rib roast in the Rational, I use a cooking program that will hold it at 125F or 130F, with an internal tempertaure probe and it will do a great job.

But Rational themselves do not recommend using the internal probe with meat less than about 2 pounds (1 kilo) weight. The temperture cycling is one reason.

Lab water baths generally maintain tempertaure to withing 0.25 degree, many to within 0.1 degree, and some of them down to 0.01 degrees. When you plop the food into the water bath the temperature drops a bit - they can't help that, but as it returns to the proper temperature it will absolutely not overshoot by more than the amounts above.

Now, do you really need 0.1 degree accuracy? No, even for critical things like salmon mi cuit, you don't need that much. However it sure doesn't hurt.

Note that most digital thermometers used in the kitchen are only accurate to plus or minus 1 degree F, and many of them plus or minus 2 degrees F.

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Jackal10 is correct - they excel for low temperatures. Mostly I use water baths between 45C / 113F (for fish), and 82C / 180F for confit.

They are great for cooking for a long time - up to 24 to 36 hours.

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This may be more than you ever wanted to know about water baths, but hopefully somebody will find it interesting.

More than that. This, and the sous vide thread you've informed so usefully, are absolutely fascinating and I suspect that you may just have sparked a mini-boom in sales of second-hand laboratory circulators. If that is the case, and you have the time and the inclination, might I suggest another project that could be worthy of your attention -- an expansion of the food safety advice you give in the main thread? An Idiots Guide to Safe Sous Vide would be indispensible for home cooks who might be tempted to pick up a used water bath.


Edited by iamthestretch (log)

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This may be more than you ever wanted to know about water baths, but hopefully somebody will find it interesting.

More than that. This, and the sous vide thread you've informed so usefully, are absolutely fascinating and I suspect that you may just have sparked a mini-boom in sales of second-hand laboratory circulators. If that is the case, and you have the time and the inclination, might I suggest another project that could be worthy of your attention -- an expansion of the food safety advice you give in the main thread? An Idiots Guide to Safe Sous Vide would be indispensible for home cooks who might be tempted to pick up a used water bath.

Don't be fooled by Nathan's relatively low post count. He's provided a treasure tove of info regarding sous-vide techniques. The topic you referenced started out with Nathan asking for advise on sous-vide cooking temps/times -- after which he provided more answers than the rest of us combined. :laugh:

I bought a Lauda MS immersion heater off of eBay (my one and only eBay purchase). There are plenty of lab water bath contraptions available, but I'm queasy about what's been processed through them. The immersion heaters have a lot less surface area to clean up. Some of the tank heaters are just nasty. :wacko:

Of course, if you can afford to buy the equipment new that's not a problem.

I submerge my immersion heater in a large (for home use, at least) stock pot. I cover the top with the lid - of course I can't completely seal it, since the heater blocks one side of the pot.

The Lauda is rated for +/- one degree C, which is plenty accurate enough for my purposes. The rated accuracy declines with the volume of water in the bath, but I haven't seen any lack of accurate temperature control even when my stock pot is full to the brim with bags of duck confit.

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I'm not a biochemist or food scientist or hygenist, but with that disclaimer

a) Keep it clean. If the food is not contaminated there is less to go wrong, and less drastic methods are needed. If you put bad food in, you get bad food out. Many pathogens excrete toxins, and if the food is bad to begin with while you may kill the pathogen, you wont destroy the toxin.

b) Acid environments are more toxic to pathogens than neutral or alkaline, so include some lemon juice, vinegar or wine if possible

c) Cooking sous-vide is pastaurising the food, assuming the seal is good, and the food cooked long and hot enough (at least 60C/140F for 12 minutes)

Heston Blumenthal in this article says

"Last week I wrote about pathogenic or bacterial contamination of meat. The trouble is that, with intensive farming and mass food production, it is far too easy for food to become contaminated. But careful cooking can eliminate this problem. If you want to pasteurise food in order to kill bacteria, all you need do is bring it to an internal temperature of 60C, but that is not quite the end of the story.

There are two critical considerations here. First, the whole piece of food - be it poultry, game, meat, fish, cheese or prepared dish - must be brought to that temperature and must be held at it for a minimum of 12 minutes. Interestingly, you can achieve the same pasteurisation even at a lower temperature - you just need to maintain the internal temperature for longer. For example, at 58C pasteurisation takes 45 minutes, so a small difference in temperature makes a huge difference to the cooking time. At Reading University, they have an amazing computer programme that can track your bacteria of choice - salmonella, campylobacter, listeria, E coli - and tell you how long you need to hold it at a particular temperature to make it safe. "

Normal food advise is to take it though the "danger zone", that is temperatures above 7C and below 60C or so as quickly as possible, especially around normal body temperatures, and many food regulations specify not more than 2 hours in the danger zone before or after cooking. In the case of sous vide, this means that the food should be brought to the cooking temperature within 2 hours of preperation and leaving refrigeration. Once cooked above 60C for at least 12 minutes it is pastaurised with the bacterial counts much reduced although not completely sterile. Treat like fresh food, and consume within 2 hours of opening the bag, unless further heated above 60C.

Very long cooking can also lead slow chemical changes including oxidation, although the amount of oxygen available in the sous-vide bag is limited, some will migrate through the plastic, Maillard reactions, leading to browning and caramel like tastes, and some fats and oils can degrade with time and temperature. None of these changes are directly biologically harmful with some desirable and deliberate, but others can make the food taste off, or change texture.


Edited by jackal10 (log)

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Regarding the evaporation of water from a container with an immersion heat source, you can simply take the cover to a metal shop and have a section cut out of the edge of the cover to accomodate the immersion unit and then get a silicone edge seal (made in various sizes for applications in both extreme heat and cold) which are good up to 600 degrees and slide that onto the cutaway edge which will effectively cut down the opening to a very small area. The seal will conform to any shape and can be cemented in place with a high temperature sealant.

We used to have a physical therapy department as part of our office and had several tanks for west hot packs and for the oversized ones we used a deep steam table pan with an immersion heater and had the cover cut the way I described. The pre-made silicone seals were not available at that time so we simply used the high temperature silicone "putty" that was available at the hardware store. It worked just fine to keep the water from evaporating.

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Regarding the concerns about food hygiene, both Jackal10 and I posted questions to Harold McGee when he most graciously visited our forum. The bottom line is that we should always be cognizant of the activity of pathogenic agents (if I may pontificate!), and the temperature of food should be monitored closely.

In other words, giving the shits to your loved ones is probably not cool. :unsure:

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How much evaporation can there be at 60C? Can't you just put some tin foil or something over the top?

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Evaporation is really not much of a concern for reasonable stretches of time. I often go to bed with the water bath happily swirling away without any worry about evaporation. My circulating heater has a "trip temperature" setting that shuts off the heater if it gets too hot.

Having said that, I would never leave the house with the water bath heater running (well at least not for more than a brief period). I've had some "incidents" where a bag of duck confit got caught in the recirculating pump, melting the bag and generating a nasty duck-fat oil-slick in the water bath. Exxon Valdez eat your heart out! :shock:

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The comments about food safety above are good, but here is my addition.

The rules of thumb about the "danger zone" are based on a mixture of good science, with a lot of well meaning safety factors and conservatism applied to make sure people don't get sick. The USDA , FDA and other health agencies are very anxious to avoid sick people, and they are aware that people have inaccurate thermometers, so they tend to oversimplify things. For example, any guide that just talks about temperature is only telling you half the story - you need to hold that temperture for a period of time to achieve food safety.

The so called food "danger zone" is not a hard and fast thing. Bacteria grow at any temperature above freezing, and they generally stop or slow down above 125F. Many experts would say that the danger zone is 30F/-2C to 130F/54C. FDA / USDA generally says 41F/5C to 140F/60C.

However, it should be noted that many very common foods are not cooked to the USDA / FDA guidelines at all. Rare beef that is "bleu" can be as low as 104F /40C, rare is usually 120F / 49C , Medium rare is 125F/52C to 130F / 54C, and so forth. Fish is cooked even less. Many chefs serve salmon mi cuit at 100F/38C to 104F/40C, while most fish is better at 113F / 45C.

If that is in the danger zone, how can that happen? How is it possible to serve food cooked at these temperature less than 140F/60C ?

There are several reasons. One is that some food is less contaminated that others. The interior of a muscle food, like beef, or even fish, is only very rarely contaminated. Ground beef is a far more serious health concern than a steak or roast as a result.

Also, because of the surface effect, the surface of a steak is much more vulnerable to contamination, but it typically is heated to a higher temperture than the interior, and held their longer (so the interior will be done). So, the FDA Food Code only requires that the exterior of a steak be brought to 145F/63C, and they don't care about the interior temperture at all (so long as the whole thing isn't held too long).

Chicken, on the other hand, is much more likely to be externally contaminated, and is more likely to have salmonella. Heston Blumenthal recommends 147F / 64C for chicken for this reason. However, the USDA (and many cookbooks following them) recommend 160F, at which point the bird is virually guaranteed to be dried out.

As the Blumenthal quote in the previous posting says, 12 minutes at 140F/60C is one standard, but there are actually a wide range of times and temperatures. Techical publications often discuss this in term of how many "log-cycles" or "D" - which means a factor of ten reduction in the bacteria. 140F/60C for 12 minutes is a 7D, or 10,000,000 factor reduction. In practice most food safety experts believe that 5D - or 100,000 fold reduction is enough, others want more.

The longer you are going to hold or store the food prior to eating, the more D you need, because during the holding time any remaining bacteria can grow back. Canned food is typically processed to 12D.

You can achieve the same results by longer time at lower temperatures, or less time at higher temperatures. Here is a table

130F 54C 112 mintues

135F 57C 35 minutes

140F 60C 12 minutes

145F 62C 4 minutes

150F 65C 1.5 minutes

165F 74C 2 seconds

Note that these are consitent with the US FDA Food Code regulations.

This shows how silly it is to give requirements in terms of temperature alone, without taking time into account. 140F is NOT SAFE if done for a very short time. It is safe done for 12 minutes. It is pointless beyond 12 minutes (unless you need more than 7D reduction).

So, if you want to cook rare beef sous vide, you need to cook until the core sits at that temperature for that long. If you use 130F/54C bath temperature, a thick fillet might well take an hour just to come up to that temperature, so that means putting it in a water bath for a total 2 1/2 - 3 hours. Then sear the outside in a pan - it is delicious this way, and the other benefit of sitting at that temperature for this long is that it will be extra tender due to collagen break down.

Meanwhile cooking below 130F for a long time period is not recommended. The highest temperature common pathogen can multiply up to 127F. However, you can still eat food cooked less than that if you don't wait too long. The flip side of cooking times/temperatures are the recommendations for holding times - i.e. if you are in the "danger zone" how long can you let it stay. The FDA recommends that in the danger zone between 41F/5C and 140F/60C, that food not spend more than 4 hours. Many souces, in an abundance of caution cut that in half to two hours, but 4 is the regulation.

A more precise chart of time and temperature is given here

This guideline explains why we can eat rare beef without getting sick - at 120F/49C the safe holding time (using similar criteria to FDA rules) is 5.6 hours. A steak which is taken from the refridgerator, prepped under clean conditions, then cooked, served and eaten in 30 minutes is well within that time period. Salmon mi cuit at 113F shouldn't sit more than 4.6 hours. Personally, I would not go anywhere close to those limits, but the interesting thing is that you don't have to for any food cooked to order in a home or restaurant.

Here is a good general guide to food safety- written for home chefs, but with a lot of interesting technical information.

Note that all of the above are for general conditions - if the acidity (pH), salinity or even sugar level is above certain values, then you don't need heat at all. That is why salt cod can stay at room temperature, and why maple syrup, or corn syrup also keeps a long time.

People cooking in restaurants have the additional requirement that health department inspectors and regulations may impose, which can often have very little to do with the reality and science of microbes. That is a different topic altogether.

Another point that I should make is that the above discussion is about times and temperatures for food that is to be served immediately. Storing food after it is cooked has another whole set of issues. When you store food for a long time after cooking, you give any remaining bacteria a chance to come back and grow. So you need to be much more careful.

When people talk about sous vide, sometimes they mean cooking for immediate service (that's what I generally do). Sometimes they mean cooking, chilling then reheating up to a week later. Storing the food after cooking, and also how you chill it and how fast you chill it require a higher degree of food saftey - it's another topic altogether.

OK, so that is my view.

For an officia, but hard to read, viewpoint you can plow through the US government version, the FDA regulations are called the "Food Code", and you can find it here. The full set of tables on times and tempertaures are found here.

They have a section on "reduced oxygen packaging" - i.e. sous vide, but it is mostly regulation speak without much information. Also, it is mainly about food sold at retail in vacuum packages.

I hope that helps.

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Nathan,

MANY thanks for the information.

What you have provided is NOT "more" than I ever wanted to know about water baths but just a good start on what I have wanted to know and have looked for more than once on Google and not found.

I especially thank you for the food safety details and references.

Actually, I suspect that many laboratories do not 'buy' equipment such as constant temperature baths and, instead, would be embarrassed at the suggestion that they could not just more easily build their own. Indeed, mostly I went looking for just the relevant parts, starting with thermocouples, electric relays, and electric stirring motors.

When I worked a summer in a biophysics laboratory, we had 'home brew' constant temperature baths. For the heating element, we just put a standard incandescent light bulb in the water. Of course, we had the electrical part out of the water. So, the bulb was 'upside down'.

So, if want 100 W of heat, then just use a 100 W bulb. Too much heat? Fine: Change to a 60 W bulb. Of course, no such set up would ever pass anything like standard electrical inspections, but that has long been common in scientific laboratories! I don't recall a bulb ever breaking while under water, but if it did then I guess we would have just depended on the circuit breaker!

Working late and then walking through the lab was errie: The lab was dark but occasionally one of the light bulbs lit.

When I was a child I had some good laboratory equipment including a ring stand and some clamps; wonder whatever happened to that stuff! Should have taken it with me when I went off to college!

It may be that getting 0.01 C temperature stability is not so easy: When I was at the US National Institute for Standards and Technology, we were doing accurate laser wavelength measurement and for our interferometer tried to keep 0.01 C stability. Our laboratory guy was very concerned about how difficult such accuracy is to achieve and basically just wanted to keep the laboratory shut with no one inside and with nothing going in or out.

I would settle just for some sources of thermocouples, thermometers, electric power relays, and stirring motors. For the tank, hoses, lids, etc., sure, just use stainless steel pots and epoxy, silicone, Teflon tape, hose clamps, etc. For a pot, once in a weak moment I bought a really cheap stainless steel stock pot. It is useless as a stock pot and is so cheap that the holes for the rivets for the handles actually leak, but seal up the holes with some silicone and the thing would make a fine container for a constant temperature bath. Also the lid is so thin that it would be easy to cut to customize.

When I overheat and ruin a Farberware pot (I have a big supply, many still new, of the old ones of stainless steel with a thick hunk of aluminum glued to the outside of the bottom, and like them a lot), I keep the old pot as a source of stainless steel scrap!

One of my pet peeves is that people selling things still have not really accepted the importance of the Internet and, thus, mostly do not seek actually to describe their products in enough detail to permit actual project design and engineering and, then, purchase and usage. Instead, the vendors seem to assume that the Internet is mostly just a calling card or first-cut brochure and that the customers either already know all about the products or will work face to face with a technical sales representative, try a bunch of products, etc. There is another problem: A surprisingly small fraction of people in business actually know how to write meaningful descriptions of their products.

These days, for a 'control', we are tempted just to connect to a general purpose PC adapter card with a digital to analog converter and some standard device driver software and write a little PC software for the control logic. Have you made some progress in this direction?

Likely one of the great fun things we are now able to do in a home shop or kitchen is to use the currently available means of connecting sensors and actuators ('transducers') to a PC and writing some simple software! E.g., put the frozen chuck roast in the oven with a sliced onion and a can of cream of mushroom soup and head off to work. When within about a hour of leaving the office, connect to the home computer and have it turn on the oven to start cooking the roast.

Better, still, would be a home computer with wheels, arms, stereo digital cameras, WiMax to a DSL modem and at the office use data gloves to remove the chuck roast from the refrigerator, unwrap it, put it in the pot, brown on the top of the stove, slice the onions, pour in the red wine and beef stock, put on the lid, set it in the oven, open the Chambertin to breath, and set out the cheese to get it up to room temperature. Instead of such progress we get, what, a new patch of a Web browser with some old outrageous security problems fixed but possibly some new ones ready to get us to have to swap again a year from now.

Of course, in the future, if we were short on onions, then we could use the data gloves to move to our second car at home and drive to the store, get an onion, drive back, and then finish the roast. For this, virtual reality at 60 MPH down the Saw Mill River Parkway, would want a really good WiMax connection! My ISP dropped the connection again? Oops.

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Many many thanks Nathanm, That is one of the best and most informative posts I have seen in a long time. I have been looking for those references...

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It was said of the first Queen Elizabeth (16th century) that she bathed once a month, whether she needed to or not.

My tuppence worth, in addtion to the very useful reams of information very usefully (and lovingly) posted above.

If you are in a professional kitchen, feeding others on a money-changing-hands basis... be very VERY careful about pathogen activity during low-temperature cooking. You may know your job, I may know mine, but remember we have a duty to demonstrate that the techniques we use are reasonably safe.

I sometimes have dealings with the Environmental Health Office (every UK chef does from time to time, usually every 6-12 months) - I presume the US Health and Hygiene people are much the same. Over here, you have to show what's called 'due diligence' - That you've taken 'reasonable steps' to guarantee the safety of the food you serve to customers.

Now, 'reasonable steps' may very from chef to chef, from dish to dish, cooking method to cooking method, and last bu not least, the EHO inspector of the moment. There are many different degrees of sailing close to the wind in your interpretation of 'due diligence', and as the UK is slowly but surely reaching a similarly litigious level of culture as the US, if we value our business we have to make sure that we are taking very carerful stock of the risks we're taking with the food that we prepare and sell.

I'm very much a Bourdain-ite with my own digestion - but since the days of the Borgias faded into history, poisoning those you host has remained both unfashionable and questionable in a commercial sense.

With that caveat aside, most EHOs I've met have been reasonable people, who appreciate a lack of bullshit and the ability to 'self-identify' points of risk in the cooking chain. I have a biochemistry degree (quite a few eGulleteers have similar scientific qualification, some a great deal more) and most EHOs know that if you have a genuine level of knowledge past the legal minimum, if you've eductaed yourself as to the risks (eG plays a part here, I think), and if you can show that your temperature checks are iron-clad, they will give you less grief than I actually thought some of my slow-cooking techniques (in past kitchens) merited from an EHO inspector.

Know what you're dealing with, please. Clostridium botulinum can kill, very easily, and low temperature sous-vide cookery (C. bot. is an anaerobe) can provide ideal conditions for it. E. Coli killed 20 people in a town a few years ago, not far from where I grew up in Scotland.

On a lighter note, most water baths I used at university are splendid pieces of kit; accurate, reliable and a pleasure to use. Be aware, though, of the old lab grumble that as soon as a medical/scientific use was found for a piece of equipment, its manfacturer charged triple for the privilege of a few extra buttons and a higher polish on the casing.

Home-made equipment, however skillfully assembled and designed, is unlikely to find as much favour with an EHO as a second-hand lab-issue water bath.

eBay, anyone?

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The references to the US FDA regulations in Nathan's excellent post above are good ammunition to help convince EHO inspectors. They give specific time/temperature processing tables.

They say "Since refrigeration alone does not guarantee safety from pathogenic microorganisms, additional growth barriers must be provided. Growth barriers are provided by hurdles such as low pH, aw, or short shelf life, and constant monitoring of the temperature. Any one hurdle, or a combination of several, may be used with refrigeration to control pathogenic outgrowth."

A restaurant or home use of water baths and sous-vide techniques, where the food is being prepared for immediate consumption is rather different from a food manufacturer preparing food for retail sale, or for long storage and use under uncontrolled conditions.

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This is a very important point. Many of the health department concerns about sous vide have to do with preparation followed by storage - eithre selling food retail to be reheated later, or preparing food in a central kitchen/factory and shipping to multiple places to be reheated.

That is VERY different than cooking for food to be served immediately.

The main reason is botulism. Botulism is the most severe form of food poisioning. It is generally NOT relevant to immediatly served food.

Botulism bacteria are quickly killed by heat - the guidelines discussed above will certainly get rid of it. However, the bacteria produce spores which are very resiliant - they require MUCH higher temperatures to kill them. This is why the procedures for home canning often involve using a pressure cooker.

Botulism generally does not affect fresh foods because it is anerobic - it can't grow in the presence of oxygen. However the spores are often present. The primary concern with sous vide food that is kept for storage is that the initial cooking and heat treatment leaves the spores intact, then while the food is stored the spores germinate into bacteria which produce toxin which can kill people who eat it.

This requires storage for a period of time - typically days. This is a real issue for sous vide intended to be stored for a long time. The food saftey issues for that form of sous vide are quite serious - it is basically food manufacturing, and you really better know what you are doing. The longer that the food is stored after cooking the more this is an issue. You need to be extremely careful about hygene, and in cases of long storage typically want to adjust the recipe accordingly - adding something acidic to help stop the bacteria growing.

Sous vide has been used this way in Europe for over 20 years so it certainly can be done. However, be aware that cooking and then storing before serving is fundamentally different and has greater potential for danger.

Generally speaking the concerns about botulism and other anerobic bacteria are not an issue with sous vide used immediately, so long as the food safety guidelines dissused above are used - i.e. 140F/60C for 12 minutes, or keeping the total time in the danger zone less than the time in the tables.

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I am a scientist in an Immunology lab at Stanford, and I would be leary about buying a used water bath for food. The water baths we have around here routinely have carcinogens, bacteria, and viral vectors thawed in them. While a good cleaning will get rid of bacteria, I would make sure to wash with bleach, both to disinfect and get rid of ethidium bromide (a common and nasty carcinogen). Then maybe a vinegar rinse, because it is the strongest acid you probably have around. I would finish with a rinse of 70% (140 proof) alcohol (pure alcohol is less anti-microbial).

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Natthanm. way back at the top of the thread you were talking about using pingpong balls or the lab equivilent and I was wondering if they're used to prevent evaporation?

Btw, this thread is fascinating and was some really great work!

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The bottom oven of a four oven AGA sits at about 60C, which I find ideal for LTLT cooking at home.

I've also seen recently a flyer about a water bath manufacturere specialising in water baths for the food and catering industry, but I can't find it. I'm surprised restaurant supply houses are not beginning to stock them.

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This is a fascinating thread, but I'm a little disappointed in the people who work in labs, and some of their advice for one niggling little point.

When we're purchasing something like a Lauda bath (I'm partial to the lauda brand), we usually call our Fisher Scientific or VWR Scientific Products International sales rep and set them to work for us.

If you have the money to purchase a new laboratory water bath to do your sous vide cooking, I would highly suggest that.

Another thing I would suggest is to get one that is intended to have the temperature controlled water pumped outside of the beast through to cool/heat something external. That will give you more flexibility to increase the size of your sous vide pot later with less expense.

Make sure the one you are looking at has a large reservoir for obvious reasons.

Make sure the one you are looking at has a large "thermal mass"

It shouldn't be terribly difficult to get in touch with one of the reps from one of those companies. Simply call a local University's science or engineering departments and ask if someone can get you the rep's contact number.

The reason I do it this way, is a good 70% of the time, we find that these reps get us a better deal than purchasing the item directly from the manufacturer.

Also, if you have a metal shop fab you some jacketed cookers that are too large for one (heaven forfend such an embarassment of riches), you can attach several of these water baths to one large cooker.

This is one of the threads that makes eGullet great. I don't know how I missed it in January.

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Fisher Scientific, Cole Palmer, VWR and others all have web sites where you can buy new lab water baths directly.

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Anyone have operating instructions for a Lauda MS?

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