Mash tun- how accurate of a thermometer is needed?

Hi, I'm in the process of switching over from extract to all grain. I already have pots, burners, and a cooler mash tun that I will be batch sparging with. I already have a digital thermometer that seems very accurate, but the mfg specs list it's accuracy at 1.8 degrees +- is that close enough? Will I be fine or is more accuracy needed? Thanks

IMHO it's fine. Other may disagree but I can't think of any time in brewing where the temperature is actualy that critical that a +/- variation of 1.8 degrees is going to matter. I doubt that anyone can tell the difference between a beer mashed at 150 and one that 's mashed 1.8 degrees higher or lower.

What might matter is how persnikity you are when it comes to accurracy. If you're kind of guy that weighs out ingredients to 3 decimal places, you might find that knowing that your temp readings have the potential to be off by almost 2 degrees is really irritating. The beer won't know or care, but you will.

MrAverage said:

If you're kind of guy that weighs out ingredients to 3 decimal places, you might find that knowing that your temp readings have the potential to be off by almost 2 degrees is really irritating.

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Whats wrong with that?? does that make me weird?

I would check the thermometer in boiling distilled water, and compare your reading with your boiling point at your elevation, I would also cross check it in icewater to verify accuracy of your thermometer.

azscoob said:

Whats wrong with that?? does that make me weird?

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Not at all. I'm one of those guys myself.

...and your suggestions re:checking the thermometer in boiling and ice water are right on.

...and your suggestions re:checking the thermometer in boiling and ice water are right on.

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You have to watch out with this also. I had a thermometer that was right on 212 and 32 but was off 6-8*F low in the 150*F range. I couldn't figure out why 3-4 batches ended up finishing at 1.020. I tracked it down to the thermometer and the fact that I was actually mashing at 160-161 when I thought I was at 154. Replaced the thermometer with a lab grade mercury one and it fixed the problem.

2* can make a big difference. Really it's all about how much you care. It's not like the beer will be ruined if you are off by a couple degrees....it just won't be exactly what it would have been if you'd hit your temp....no biggie, but depends on how much that matters to you.

Thanks for the tips. I have already tried it in boiling and freezing water and both are within a couple 1/10ths of a degree. That's why I thought it was fairly accurate, but I have not checked it at mash temps. I will have to find a known good thermometer to check it against. Thanks, I think I should be ok with my current thermometer

Another thing to consider: Just because the accuracy specs are +/- 1.8 degrees doesn't necesarily mean that it will be off by that amount. It could be right on or off by less than that. That's just the manufacturer's accaptable range of tolerance for that product.

Go forth and worry not.

So long it's consistent. If you do a single infusion at 152 and it finishes too high you'll drop the temp a degree or two next time. If the temp was really 153 or 151 is not that important so long you don't keep changing thermometers.

I don't think that there's a good reason to stick to a 1.8 degree accuracy thermometer, when a new alcohol lab thermometer can be had for under $10...

M_C

Go to a Kitchen supply store, where chefs buy their gear. You can get a Taylor brand digital for $15. They are waterproof and accurate and more importantly, won't break under normal use. A glass thermometer is just dumb, sorry.

Those $10 lab thermometers even with a certificate of accuracy are rated for +/- 1 degC. You will have to pay for thermometer guaranteed to be more accurate.

Northcalais40 said:

Go to a Kitchen supply store, where chefs buy their gear. You can get a Taylor brand digital for $15. They are waterproof and accurate and more importantly, won't break under normal use. A glass thermometer is just dumb, sorry.

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Not as a calibration device it isn't. Having no idea if your thermometer is accurate in the mash range is dumb.

_

Nah, its ignorant, not necessarily dumb.

JRems said:

Thanks for the tips. I have already tried it in boiling and freezing water and both are within a couple 1/10ths of a degree. That's why I thought it was fairly accurate, but I have not checked it at mash temps. I will have to find a known good thermometer to check it against. Thanks, I think I should be ok with my current thermometer

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I think if it's accurate in boiling and iced water, it's also going to be accurate at all points in between.

-a.

ajf said:

I think if it's accurate in boiling and iced water, it's also going to be accurate at all points in between.

-a.

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Not necessarily

Oh, come on . We're not saving lives here. If it is accurate as ajf describes, its accurate enough for me.

I think if it's accurate in boiling and iced water, it's also going to be accurate at all points in between.

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I can assure you that this is not always true. I had personal experience with one that was not accurate from ~125F-~190F but read right on 212 and 32. I have no idea why or how, just that it happened and I saw it with my own eyes. It took me about a month of daily backtracking to figure out what was going wrong and why my beers weren't finishing out. Replaced the thermometer and been good ever since.

o4_srt said:

Not necessarily

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Why not?
I don't mind you disagreeing, but back it up with some facts.

-a.

MachineShopBrewing said:

I can assure you that this is not always true. I had personal experience with one that was not accurate from ~125F-~190F but read right on 212 and 32. I have no idea why or how, just that it happened and I saw it with my own eyes. It took me about a month of daily backtracking to figure out what was going wrong and why my beers weren't finishing out. Replaced the thermometer and been good ever since.

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Let me ask you, how do you know that your thermometer was inaccurate between ~125F-~190F?
The fact that you changed your thermometer, and the problems went away doesn't mean that the thermometer was wrong. It just means that something changed.
Did you compare the readings with the new thermometer against the old at temperatures between 125 and 190F?
If you did and they were different, how do you know which one was accurate?

-a.

ajf said:

Let me ask you, how do you know that your thermometer was inaccurate between ~125F-~190F?
The fact that you changed your thermometer, and the problems went away doesn't mean that the thermometer was wrong. It just means that something changed.
Did you compare the readings with the new thermometer against the old at temperatures between 125 and 190F?
If you did and they were different, how do you know which one was accurate?

-a.

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Does comparison to lab grade, yearly calibrated thermocouples and thermometers at my place of employment count as proof that a thermometer can be calibrated at freezing and boiling but not at all points between the two?

Let me ask you, how do you know that your thermometer was inaccurate between ~125F-~190F?
The fact that you changed your thermometer, and the problems went away doesn't mean that the thermometer was wrong. It just means that something changed.
Did you compare the readings with the new thermometer against the old at temperatures between 125 and 190F?
If you did and they were different, how do you know which one was accurate?

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I compared it to a lab grade glass thermometer throughout all temp ranges. The one that was bad was a cheap metal one from the HB shop. I can assure you that nothing else changed in my process other than the thermometer and things have been better since.

And don't trust these style either. http://tinyurl.com/67ra8vh

I bought one of these and it was 20*F off over all temp ranges to 212(I didn't care about anything over that)
I noticed it when I knew the temp outside was 65-70*F and the thing was sitting on the workbench reading in the mid 40s. I then compared it to both of the others and it was completely wacked. Brand new and brand new battery.


YMMV