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Sous Vide: Recipes, Techniques & Equipment (Part 5)

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#571 Camano Chef

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Posted 14 July 2009 - 01:37 PM

Down the page is indicated "*Temperature range and stability vary depending on bath volume, surface area, insulation and type of fluid.
Notes: Performance specifications determined at ambient temperature of 20ºC/68ºF."


I understand "temperature range" = "temperature precision".
Should we also have to conclude that Polyscience machine cannot assess the quantity of water contained in a container, the ambient temperature...and therefore Polyscience can't guaranty temperature precision?

Jean-François

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Jean-Francis

I have a Polyscience immersion circulator. It usually is used in a 20 Liter All-Clad brand stock pot. I have the stock pot wrapped with about 1/2" (12MM) bubble type aluminized insulation. The top is covered with a 1/4"( 8mm) plexiglass sheet that I cut out to fit tightly around the Polyscience circulator in order to reduce evaporation water loss. I have run this unit for at least 24 hours without more than 1/2" (12mm) water level loss.

The Polyscience circulator easily maintains 90C in this water bath. ( the highest I have used so far.)

I have tested the temperature variations in the water bath using a Thermoworks Microtherma 2 thermometer and find the temperatures within .5C in all locations.

I think that my water bath is probably larger than is typical but my results seem to confirm the capability and accuracy of the Polyscience immersion circulator. I do feel the larger mass of water makes the whole system much more stable. For example dropping a 2# (approx 1 kilo) frozen pot roast into the bath never drops the temperature more than .5C and that is for just a few minutes.

The unit is so dependable that I never hesitate even the longest (up to 48 hours) cook times.

I hope my observations are helpful.

Phil

#572 Scout_21

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Posted 15 July 2009 - 07:32 PM

"I understand "temperature range" = "temperature precision".
Should we also have to conclude that Polyscience machine cannot assess the quantity of water contained in a container, the ambient temperature...and therefore Polyscience can't guaranty temperature precision?"


I do not think that temperature range = temperature precision. The polyscience circulator (all circulators for that matter) have some upper limit of the volume of the liquid they can heat to a given temperature. For example no immersion circulator I know of can heat a million liters of water to 99 C. As for the precision (or repeatability of measurement) I can say that my polyscience (and laudas and some other immersion circulators I have used) is quite precise by multiple comparisions of its stated temp to that of several external thermometers.

By your previous posts you mention something about being at the "correct temperature." I think you mean accuracy. Again with external devices I can safely say that the polyscience is quite accurate as well. At least to the needs of any amateur (and many, many professional) chef(s).

I also do not see why an immersion circulator would need to know the volume of the bath or the air temperature to work properly....it is the temp of the cooking fluid that you want to control and maintain. Even 3-4000 dollar circulators used for scientific purposes do not take into account air temp or need to "know" the amount of liquid in the bath (please correct me if I am wrong). In any instance there is some level of error that has to be accepted.

Any immersion circulator (for cooking needs) such as Polyscience, Lauda, etc. should have more than enough accuracy and precision to work. I do not think that control down to .001C is really needed to produce excellent results.

I hope I haven't been rude...just a long day of research....and I do really hope this helps in some manner.

Cheers

#573 Paul McMichael

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Posted 15 July 2009 - 07:47 PM

I do not think that temperature range = temperature precision.  The polyscience circulator (all circulators for that matter) have some upper limit of the volume of the liquid they can heat to a given temperature.  For example no immersion circulator I know of can heat a million liters of water to 99 C.  As for the precision (or repeatability of measurement) I can say that my polyscience (and laudas and some other immersion circulators I have used) is quite precise by multiple comparisions of its stated temp to that of several external thermometers.

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The issue is the effect of time on the tuning parameters of the controller. When I put my 1KW circulator in the regular 10 liter bath, it responds quickly in a 0.4 degree F range. When I mount it in a large poly cooler (~50 liters) it is much slower and reset functions cause greater over and under shoot. There is no problem heating a million liter bath, if your insulation is adequate.

Paul

#574 Scout_21

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Posted 15 July 2009 - 09:45 PM

I would love to see this insulation...how large of an R-value?

I'm surprised that your circulator does not stabalize with a large amount of water in an insulated container. One would think that the thermal mass would prevent a great amount of under and over shooting. Perhaps the PID on your device is having some issues?

#575 KennethT

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Posted 16 July 2009 - 02:35 PM

I do not think that temperature range = temperature precision.  The polyscience circulator (all circulators for that matter) have some upper limit of the volume of the liquid they can heat to a given temperature.   For example no immersion circulator I know of can heat a million liters of water to 99 C.  As for the precision (or repeatability of measurement) I can say that my polyscience (and laudas and some other immersion circulators I have used) is quite precise by multiple comparisions of its stated temp to that of several external thermometers.

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The issue is the effect of time on the tuning parameters of the controller. When I put my 1KW circulator in the regular 10 liter bath, it responds quickly in a 0.4 degree F range. When I mount it in a large poly cooler (~50 liters) it is much slower and reset functions cause greater over and under shoot. There is no problem heating a million liter bath, if your insulation is adequate.

Paul

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Paul - yes, of course the same 1KW of power will take much longer to heat 5X the volume of water, and that mass of water will take much longer to cool - so it's slower to respond in general. However, if tuned properly, your circulator should not overshoot or undershoot much more than normal. Do you autotune it each time you change bath sizes? In theory, every time a parameter changes, (i.e. the bath size changes, or you add insulation to the bath, or you decide to cover it when it was tuned uncovered, etc., ) you should re-tune your circulator parameters, otherwise, it will use the same parameters for all situations, which is not a good fit. Or, if you constantly alternate between a couple of situations, you should autotune each and copy down the settings. That way, when you change situations, you can just enter in the new settings as opposed to running a lengthy autotune every time.

#576 Sousvidecooking.org

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Posted 16 July 2009 - 04:23 PM

KennethT,

I agree with you. The temperature controller of an immersion circulator (such as Julabo and Polyscience) has a fix parameter which cannot fit to all kind of water volume. Therefore the PID will never be 100% optimized.
Do you know if an automatic adaptative temperature PID controler (according to the amount of water) is sold on the market?

Jean-François
http://www.Sousvidecooking.org a blog about cooking sous vide with low and constant temperature.

#577 KennethT

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Posted 16 July 2009 - 05:42 PM

Jean-Francois - most circulators have an 'auto-tune' function - you just have to read the manual to find out how to initiate it. Once you run the auto-tune (the process takes about an hour, usually), the circulator will set the P, I and D values, along with some other values, into memory that work best for the situation it was tuned with. These values tell the heater how much power and how fast to react to any changes in the system - like adding a cold piece of chicken. Changing anything, liek the water volume, insulation of the vessel, covered vs uncovered, etc. will necessitate changing these values since it will affect how fast the volume of water heats and cools.

For instance, let's say you have a heavily insulated vessel that is covered to minimize evaporation... well, evaporation is a cooling process, so the less water that evaporates, the less heat the system needs to keep it at the same temperature. If you take the cover off, you get more evaporation, more cooling, hence the heater has to run with more power to keep the temperature of the system stable.

I guess the bottom line is to read the manual and find out how to turn on the auto-tune function with your circulator. If, for some reason, yours doesn't have an autotune, then I suggest reading a bit about how to set the PID values and play around with it to get it to work properly. There's tons of information on the internet and I think somewhere in this thread about how to tune your PID system. Maybe you want to try a search in this thread for "autotune" or "tune" or something.....

Hope this helps...

#578 Paul McMichael

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Posted 16 July 2009 - 07:01 PM

My circulator has fixed settings - no auto tune. But for $30 on ebay, I cannot complain too much. Only my Bradley smoker has full PID control.

They make PID controllers that accept parameter inputs from an external computer. With a proper level detector you can build an adaptive controller.

#579 Sousvidecooking.org

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Posted 16 July 2009 - 11:33 PM

KennethT,

I checked the manual of my Julabo EC and I can't find any tune function. I also searched on google for "Julabo EC PID tuning" but could not find anything relevant. It seems Polyscience 7306C manual cannot be downloaded from Polyscience site. Could someone tell me if the Polyscience 7306C benefits from tune or autotune functions?

Jean-François
http://www.Sousvidecooking.org a blog about cooking sous vide with low and constant temperature.

#580 Werdna

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Posted 17 July 2009 - 12:09 PM

I'm wondering if anyone has used sodium nitrate in sous vide applications to prevent the greyish color of beef/pork/etc after a long slow cooking? I'm doing some reading up on it and it looks like it might be a good idea to add some ascorbic acid as well to retard nitrosamine formation, as well as for its antioxidant properties. But then high acid content can cause the meat to turn greyish as well..

I'm also considering a short (1-2 hour) initial cooking at ~115F 'cause McGee is saying that the myoglobin reacts around 120, and if you heat it up slow then the other proteins are mostly done reacting and less reactions occur to change the color when you hit 120.

Anyone play around with this and color retention? I'm thinking about cooking very-thin sliced meats (mexican-grocer-bbq style cuts) for a long time, and searing on these I consider kinda counterproductive texture-wise.

#581 nathanm

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Posted 18 July 2009 - 02:50 PM

most circulators have an 'auto-tune' function - you just have to read the manual to find out how to initiate it.  Once you run the auto-tune (the process takes about an hour, usually), the circulator will set the P, I and D values, along with some other values, into memory that work best for the situation it was tuned with.  These values tell the heater how much power and how fast to react to any changes in the system - like adding a cold piece of chicken.  Changing anything, liek the water volume, insulation of the vessel, covered vs uncovered, etc. will necessitate changing these values since it will affect how fast the volume of water heats and cools.

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I agree with this, but there is some variation here.

Some older PID controllers, water baths, or immersion circulators have no auto-tune function. This is true of many of the used baths on eBay.

Many circulators with a built-in tank for the bath have no autotune function because the bath size can't change. They still ought to have auto-tune becase different fluids will lose heat differently, but many don't.

There are also "continuous autotuning" or "adaptive autotuning" or just "adaptive" controllers that are constantly in autotune mode - you never need to tell it to autotune, it figures it out for itself. Some controllers boast fuzzy logic or neural network controllers - these are common variations on adaptive control.

Adaptive control is best because it simply adapts to the situation at hand no matter what. However this is only very new and high end PID controllers and/or high end water baths or immersion circulators that have this feature.

None of the systems "knows" how much water is there, because that isn't relevant. What is relevant is how much heat from the heating coil does it take to change the temperture in the bath. During autotuning (or during adaptive autotuning) the controller tries to calibrate how much heat it takes to raise the temperture.

The relationship between heat in and temperature depends on many factors - temperature of the bath, temperature of the room, degree of insulation, size of the water, initial tempertaure, surface area, is the bath is covered with a lid (changes evaporation), what liquid is in the bath (water evaporates, oil does not), how much cold food is in the bath and so forth.

Any of those factors can effect the heating performance, and thus the PID parameters. However, PID controllers without an autotune can still do a pretty good job, so don't despair if your bath doesn't have this feature.
Nathan

#582 nathanm

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Posted 18 July 2009 - 02:54 PM

I'm wondering if anyone has used sodium nitrate in sous vide applications to prevent the greyish color of beef/pork/etc after a long slow cooking?  I'm doing some reading up on it and it looks like it might be a good idea to add some ascorbic acid as well to retard nitrosamine formation, as well as for its antioxidant properties.  But then high acid content can cause the meat to turn greyish as well..

I'm also considering a short (1-2 hour) initial cooking at ~115F 'cause McGee is saying that the myoglobin reacts around 120, and if you heat it up slow then the other proteins are mostly done reacting and less reactions occur to change the color when you hit 120.

Anyone play around with this and color retention?  I'm thinking about cooking very-thin sliced meats (mexican-grocer-bbq style cuts) for a long time, and searing on these I consider kinda counterproductive texture-wise.

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Sodium nitrate surely works, but it gives a ham-like taste to meat, not just color change.

Heating to 115F for a while does promote some enzyme action, and acts to tenderize meat. I have tried this for tenderness and it works, but I have not noticed a color retention difference.
Nathan

#583 Scout_21

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Posted 22 July 2009 - 03:25 PM

I just got an e-mail back from Polyscience. Their 7306C's PID parameters will alter based on feedback from the RTD temp sensor.


The 7312 (about $1000USD more expensive) has a more advanced autotune function that will also incorporate data on the viscosity of the liquid being used and the volume of the bath to adjust the PID settings. I do not know if you have to manually enter the viscosity data or if it has some sensor in the pump. You do have to enter the volume of the bath though.

So basically the 7306 has a continuous autotune feature and the 7312 has a continuous sutotune that can incorporate info on the fluid and the volume. Probably why the the stability of the 7312 is +/-0.01 C while the 7306 is +/-0.05C

Not sure about fuzzy logic or neural network controllers. I've only seen those mentioned with the heating/cooling baths.

That's all the info I got. If anyone has anymore info please correct me.

Cheers

 

 

 

 

[Moderator note: This topic continues in Sous Vide: Recipes, Techniques & Equipment (Part 6)]


Edited by Mjx, 24 July 2013 - 02:16 AM.
Moderator note added.






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