Crock pot with accurate temperature control

[e_monster]

I am wondering when using an immersion heater, I wonder if it doesn't make sense to bring the water close to the target temperature on the stove and then turn the stove off and let the immersion heater/PID combo maintain the temperature.

If one has a gas stove, it is probably more energy efficient as well to do that since a gas stove is a more energy efficient heat source than an electric immersion heater.

Have you tried that?

[arbeck]

I am wondering when using an immersion heater, I wonder if it doesn't make sense to bring the water close to the target temperature on the stove and then turn the stove off and let the immersion heater/PID combo maintain the temperature.

If one has a gas stove, it is probably more energy efficient as well to do that since a gas stove is a more energy efficient heat source than an electric immersion heater.

Have you tried that?

←

That's what I'd do. It can't take much power to keep the water at the right temperature, but getting it there could be a problem. For added efficiency, you could also wrap your stock pot in the rolls of aluminum duct insulation they sell at the hardware stores. In fact I might have to try this with my 16qt stock pot if I ever find the crock pot too small.

[slkinsey]

I am wondering when using an immersion heater, I wonder if it doesn't make sense to bring the water close to the target temperature on the stove and then turn the stove off and let the immersion heater/PID combo maintain the temperature.

If one has a gas stove, it is probably more energy efficient as well to do that since a gas stove is a more energy efficient heat source than an electric immersion heater.

Have you tried that?

This is exactly what I do. I bring the water bath up to within 1C of the target temperature on the stove. I've also considered leaving the burner on low -- too low to maintain the temperature, but high enough that the circulator's heater has a very reduced workload and is mostly for accuracy.

[DouglasBaldwin]

I'd be curious to see some numbers on bath heterogeneity, as I'm currently trying to figure out the best compromise for a cheap(ish) water bath (leaning towards the stovetop mod).

←

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.

Edited January 11, 2008 by DouglasBaldwin (log)

[TheSwede]

 

...

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.

←

That is interesting! As I said above I tried using a small submersible circulation pump. It worked extremely well, but died on me when I let it run in 82 C for 8 hours. Not entirelly suprising. When you use an air pump, you don't put any heat sensitive parts into the water.

[Mallet]

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.

←

Welcome to eGullet, Douglas! This is exactly the sort of information I've been looking for.

[e_monster]

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.

Thanks for the post. I just received my Auber Instruments controller Sat. and I am impressed at the stability with my 6 qt presto multi-cooker. I am going to try an immersion heater in a large pot of water (that will by brought to temp on the stove).

Where did you place the airstone?

Did you use a little one? (Any pictures of your set-up?)

Do you use any kind of 'rack' to keep the food off the bottom of the pot?

Anyone know where one can find those little immersion heaters? I tried a few hardware stores and Target with no luck.

Thanks,

E

[DouglasBaldwin]

Where did you place the airstone?

Did you use a little one? (Any pictures of your set-up?)

Do you use any kind of 'rack' to keep the food off the bottom of the pot?

←

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.

Edited January 14, 2008 by DouglasBaldwin (log)

[e_monster]

Thanks Douglas

[ChefCrash]

Anyone know where one can find those little immersion heaters? I tried a few hardware stores and Target with no luck.

I'd try places that sell camping equipment.

[e_monster]

What kind of immersion heater?

←

One similar to this one ($ 5):

http://www.amazon.com/Nordic-559-Immersion...JGCWREHKMQ12ZMW

←

I looked at an immersion heater like that at the store and I have a couple of questions. It looks like the one I saw is very much like the Nordic one and is designed to hang over the side of the cup with the handle staying dry:

1) The one that I saw seems to have a tiny little "trip-wire" (for lack of a better term) near the junction of the handle and heating element that would cause it to shut off if the heater were completely immersed

2) Since these aren't designed go be totally immersed, is the seal where the cord enters the unit waterproof enough?

Could you post a picture of your immersion heater in action?

Thanks,

E Monster

[TheSwede]

My heater has no kind of auto turn of mechanism. It has a a small plastic fork like thing where the heating element meets the handle. You hang that fork on the edge of the pot and the heater stays in place. It looks like a waterproof seal where the cable meets the handle but I wouldn't be entirelly comfortable submerging the whole thing.

Sorry, no photos of that particular setup. But basically the heater just hangs on the edge of a pot and the submersible (now burnt out...) small pump is attached to the side of the pot with suction pads.

[e_monster]

My heater has no kind of auto turn of mechanism. It has a a small plastic fork like thing where the heating element meets the handle. You hang that fork on the edge of the pot and the heater stays in place. It looks like a waterproof seal where the cable meets the handle but I wouldn't be entirelly comfortable submerging the whole thing.

Sorry, no photos of that particular setup. But basically the heater just hangs on the edge of a pot and the submersible (now burnt out...) small pump is attached to the side of the pot with suction pads.

←

Thanks for the clarification. I am glad I asked. I mistakenly thinking that you were completely submerging the thing.

What size/how deep was the pot that you were using this with?

[TheSwede]

Five or six quarts perhaps (not home right now)? Since I had a pump, it didn't really matter that the heater was only submerged halfway down in the pot.

Heating from tap water temperature up to working temperature did take some time, but was entirelly doable if you weren't in a hurry.

[DouglasBaldwin]

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.

[e_monster]

I wanted to post an update on my experiments. I am about 20 hours into a 147F cook using a 12 qt dutch oven and a 300 W immersion heater, Auber instruments controller, airstone, and a gas stove.

I have found that the immersion heater is not strong enough even at 100% power (i.e. plugged directly into the wall) to maintain, let alone heat, the water in the stockpot BUT if I set the gas flame very very very low (at which setting the gas flame is not quite enough to maintain temperature). the immersion heater controlled by the Auber instruments controller adds enough heat to maintain temperature. I have set P to 0 since at any higher setting, the setup cannot maintain the temperature.

With this setup, there is more temperature cycling than when I use my 6 qt Presto multicooker (where the temperature appears to stay constant) because the immersion heater is a bit underpowered for this particular application and takes longer to make up for heat loss..

So, with a pot of this size, the immersion heater is a decent solution when used with another very low constant heat source but not enough by itself (whereas it would be fine in a pot of the size that TheSwede used). Also, the temperature cycling might not be ideal for cooking something like eggs but then again for eggs I wouldn't need to be using a large pot.

In the pot I am using, I can do a small brisket (about 4 lbs). So, the immersion heater plus aquarium air pump seems to be a nice inexpensive solution for small pots but not ideal when one needs a larger pot.

I'll update as my experiments continue.

[Joe Blowe]

Maybe something like this would be better suited for your experiment...

[e_monster]

Maybe something like this would be better suited for your experiment...

←

Thanks for the response. It probably would be the right thing if I knew of a safe way to mount/house it and connect it to power in a safe way.

If anyone has ideas how to easily and inexpensively do that I'd love to know about it.

Preferably, one would be able leave the lid on the pot (even loosely) since that reduces power consumption considerably.

[dougal]

I wanted to post an update on my experiments. I am about 20 hours into a 147F cook using a 12 qt dutch oven and a 300 W immersion heater, Auber instruments controller, airstone, and a gas stove.

...So, with a pot of this size, the immersion heater is a decent solution when used with another very low constant heat source but not enough by itself ...

←

Would there be any problem using *two* of the 300w heaters (controlled together, as though one 600w) ???

Or three.. ?

ADDED: A charity/junk shop pan (of about the right size) could donate its lid to be customised to provide openings for heater(s) probe, etc...

Edited January 18, 2008 by dougal (log)

[e_monster]

I wanted to post an update on my experiments. I am about 20 hours into a 147F cook using a 12 qt dutch oven and a 300 W immersion heater, Auber instruments controller, airstone, and a gas stove.

...So, with a pot of this size, the immersion heater is a decent solution when used with another very low constant heat source but not enough by itself ...

←

Would there be any problem using *two* of the 300w heaters (controlled together, as though one 600w) ???

Or three.. ?

ADDED: A charity/junk shop pan (of about the right size) could donate its lid to be customised to provide openings for heater(s) probe, etc...

←

Adding more immersion heaters could work but isn't the right solution for me, personally. For me the solution of adding more and more of the 300 watt immersion heaters would be less than ideal -- the cost would then approach the cost of getting something like the 18 qt roaster Auber mentions in its application notes (they can be had for about $40 new and even less in thrift shops) or of the Hamilton Beach multicooker that is basically an immersion heater. The solution would also get messy and require using extension cords which is best avoided for long cooks since they can be fire hazards (the immersion heaters say clearly that they aren't to be used with extension cords)

Using a single water heater element like JB mentioned is an interesting idea to me -- but I am not really sure how to put together an appropriate housing for the element that would ensure that it is safe. I hope someone out there has an idea.

If anyone has ideas about putting together a reliably waterproof enclosure for the power junction, please post it.

The other thing that I have wondered about is aquarium heaters. But I haven't found one (at least not an inexpensive one) those thermostat can be turned off (and all of the ones I have seen have a maximum temperature that is far too low).

[dougal]

Personally, I wouldn't be too worried about the fire hazard of extending the cable run, or using two heaters... BUT it would scare me silly to be leaving a live mains power cable over a gas flame for many hours!

Just goes to show that we all have different risk tolerances, I suppose.

I did wonder about the idea of putting the stockpot into an insulated container (like an insulation filled cardboard box), but Auber's Application Note indicates that one should expect better control with a greater energy throughput -- but I suspect that this may principally relate to the effectiveness of convection mixing to spread the heat.

ANYWAY... the reason for digging up this thread was to note that, with all this publicity, Auber are now out of stock (likely until March) on both models of ready-to-run PID.

[jackal10]

I have purchased an Auber Instruments unit, and its excellent.

Nice people to deal with as well, and delivery no hassle despite being overseas (UK).

It makes me question why, if these people can make it in small batch quantities for $99, which means I guess the bill of materials must be more like $30 for volume, and a rice cooker is say $15 from Amazon, then why cant domestic equipment manufacturers make an accurate cooker, or laboratory water bath manufacturers (who are entering the sous vide cooker market) make one selling for, say $150...

[arbeck]

Well they probably could make one for that price. It wouldn't surprise me that you could increase the cost of a crock pot by 20 or 30 dollars and add some sort of circulation and a PID temperature control instead of the simple hi-med-low settings.

The question would be, what is the market for such a device? I don't know many people who are interested in buying one. Most people who I explain sous vide to think I'm crazy. If they are only going to sell a few thousand a year, it's not worth it.

The other thing that may be an issue is liability. If you aren't careful and don't follow the instructions, you could cook something this way and do some damage to yourself or others. Imagine the first lawsuit when someone cooks something at 135F but the sensor was malfunctioning and it's actually at 120F. Someone put some herbs in there, and then they get botulism.

[Smithy]

Hmmm, a slow cooker like this one also looks interesting:

http://www.shoppingwarehouse.net/prod-1221...ice#description

However, the description doesn't say if you actually can set the temperature and in what ranges. And there is no telling how accurate it is.

←

*bump*

I am now in the unfortunate position of being able to report on this particular slow cooker. (Hamilton Beach 6-qt Set 'n Forget Programmable)

The temperature setting is a cruel hoax. The cooker only has 3 thermal settings: high, low, and keep warm. In temperature probe mode, you set the desired temperature - and when the probe senses that temperature, the cooker turns down to "warm". Which is pretty low.

You can set the cook time under timed mode, and when it reaches the end of the cook time it will turn down to "warm". That's all the "timed cook" mode does, though: you can't program it to turn on at a specific time.

I still don't know the set points of the 3 heat settings, and it isn't worth trying to work it out. This cooker will not maintain a specified temperature. It's going back.

Edited to add the make and model, in case the link I quoted above quits working.

Edited November 23, 2008 by Smithy (log)

[e_monster]

The plug-n-play PIDs from Auber Instruments or Sous Vide Magic work great and are probably the only way to turn a crockpot or similar into a reliable sous-vide tool.

Hmmm, a slow cooker like this one also looks interesting:

http://www.shoppingwarehouse.net/prod-1221...ice#description

However, the description doesn't say if you actually can set the temperature and in what ranges. And there is no telling how accurate it is.

←

*bump*

I am now in the unfortunate position of being able to report on this particular slow cooker. (Hamilton Beach 6-qt Set 'n Forget Programmable)

The temperature setting is a cruel hoax. The cooker only has 3 thermal settings: high, low, and keep warm. In temperature probe mode, you set the desired temperature - and when the probe senses that temperature, the cooker turns down to "warm". Which is pretty low.

You can set the cook time under timed mode, and when it reaches the end of the cook time it will turn down to "warm". That's all the "timed cook" mode does, though: you can't program it to turn on at a specific time.

I still don't know the set points of the 3 heat settings, and it isn't worth trying to work it out. This cooker will not maintain a specified temperature. It's going back.

Edited to add the make and model, in case the link I quoted above quits working.

←