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Old 01-14-2011, 08:36 PM   #1
MTHarrington
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Default thermocouple mash tun reading problems

I have been getting some variable temperature readings in my mash tun with a type K thermocouple probe.

http://www.auberins.com/index.php?ma...products_id=27

I mash in, stir the holy hell out of the the mash and then take a reading
and often times I get about about 10 degrees of variability with my thermocouple. Never do I get that sort of variability in say, my hot liquor tank.

My mash tun is a big 60 qt Igloo ultratherme cooler, so it shouldn't be leaking that much heat.

Anyone know if there is some sort of interaction going on with the probe? Could I really still have heat gradation that big even after a good stirring?

If I put in a dial thermometer, of course I get a less jumpy reading.. but I'm not sure if that's because it's so slow...

I am thinking somehow, there is some sort of interference going on with the type K probe..

Ideas? This has been frustrating, because it seems I cannot trust my K probe to give me a good read, and sometimes I get pretty nervous that I might have overshot my temp and decreased my fermentability.

Maybe I just need to dump the thermocouple and get something like this:
http://www.etundra.com/Waterproof_Po...er-P15959.html

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Old 01-14-2011, 08:44 PM   #2
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I noticed quite a difference in temperature in the mash even with my long stem dial thermometer and I was doing "boil in a bag" so I had a very liquid mix and i stirred like mad. Eventually it evened out. I had a short stem digital in the same mash but reading nearer the top because of the short stem and I was seeing 5 to 10 degrees difference between the tow thermometers.

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Old 01-15-2011, 04:23 PM   #3
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The mash requires considerable time for the temperatures to even out. This can take from 10-15 minutes even with thorough stirring. The grain bed temperature will likely never be completely uniform throughout when doing the infusions. A good average temp close to your target is about the best you can expect and it is also plenty good enough. Stirring well and often is good, but it is also a trade off as every time you open the cooler lid, heat will escape. I've found it best to stir well initially at dough in and once again prior to running off the wort. Do a short vorlaugh before running off the wort after you stir things up.

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Old 01-16-2011, 11:25 AM   #4
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I switched from a herms to motorized stirring direct fired to minimize temperature stratification and reduce step lag times. I use 2 "K" t/c's one about an inch above the false bottom and one about 1/4 lower than the top of the mash. It takes my system about 10 minutes to get to a < 2dgf differential. So I think your temperature variations are accurate, assuming you are using a sheathed probe and the correct instrumentation to read a K thermocouple.

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Old 01-16-2011, 11:57 AM   #5
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Quote:
Originally Posted by jdieter View Post
I switched from a herms to motorized stirring direct fired to minimize temperature stratification and reduce step lag times. I use 2 "K" t/c's one about an inch above the false bottom and one about 1/4 lower than the top of the mash. It takes my system about 10 minutes to get to a < 2dgf differential. So I think your temperature variations are accurate, assuming you are using a sheathed probe and the correct instrumentation to read a K thermocouple.
How do you manage to stir the wort below the false bottom? Seems to me that overheating/scorching of the unstirred wort would be a problem when direct firing such as you describe.
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Old 01-16-2011, 12:04 PM   #6
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If you have any kinks in the thermocouple wire you'll get varying readings that will jump ten to twenty degrees. I have a dial thermometer and the same k type thermo hooked up to a PID in my electric kettle. Once in a while I'll get a drastic difference in the two readings, so I gently move the thermocouple wire around until the two are within a degree or so. Takes only a few seconds to fix so I've never tried anything to remedy it permanently. As far as interference goes, my thermocouple runs parallel and crosses the 220v supplies coming into my boil kettle and hot liquor tank and I haven't found that it causes any harm to the accuracy of the temp probe.

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Old 01-16-2011, 02:32 PM   #7
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cat22, my stirator is a dual paddle that sweeps appx. 1/8" above the false bottom. With constant motion I haven't encountered any scorching. I also have a nylon strainer on top of the fb so no grist can get past the fb. The nylon is cut from paint strainer bags and clipped around the perimeter of the fb with small 18ga ss pieces bent in a u shape. So to answer your question I don't stir below the false bottom but there is eonough mash movement to eliminate scorching. My stirator motor is 20rpm, I'll tried a 50rpm and the differential was zero but it was too fast with the mash splashing around everywhere, I would like to try a 30rpm if I ever find the correct motor.

JayBullen the reason for erratic readings with a kinked t/c lead wire is most likely another junction is being created, The Iron and Constantine (I think that's a K t/c) should only be joined at the tip.

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Old 01-16-2011, 02:45 PM   #8
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Quote:
Originally Posted by jdieter View Post
cat22, my stirator is a dual paddle that sweeps appx. 1/8" above the false bottom. With constant motion I haven't encountered any scorching. I also have a nylon strainer on top of the fb so no grist can get past the fb. The nylon is cut from paint strainer bags and clipped around the perimeter of the fb with small 18ga ss pieces bent in a u shape. So to answer your question I don't stir below the false bottom but there is eonough mash movement to eliminate scorching. My stirator motor is 20rpm, I'll tried a 50rpm and the differential was zero but it was too fast with the mash splashing around everywhere, I would like to try a 30rpm if I ever find the correct motor.

JayBullen the reason for erratic readings with a kinked t/c lead wire is most likely another junction is being created, The Iron and Constantine (I think that's a K t/c) should only be joined at the tip.
I would never have guessed that what you have described would work very well. That's a very innovative approach, especially using the paint strainer over the false bottom. Never thought of doing that before. I may have to give it a try.
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Old 01-16-2011, 07:38 PM   #9
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Quote:
Originally Posted by jdieter View Post
So I think your temperature variations are accurate, assuming you are using a sheathed probe and the correct instrumentation to read a K thermocouple.
Interesting.

Well, I guess that explains a lot. I've always seen this variability - and seems to settle down a 1/2 hr later.. or so. Surprising this isn't referenced in Palmer's book or the like.
Was hard for me to figure out if this was an instrumentation issue or what.

Initially I thought it was because of my sh*tty thermometers, so I was more confused when I finally got a type K thermocouple and reader (it's a Cole Palmer)
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