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Old 02-17-2008, 06:01 PM   #1
Oct 2006
Western slope of Pikes Peak
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This may seem like a silly question, but I'm just curious how everyone measures their mash temps. When I started all-grain, I used an analog instant read thermometer, but kept getting inconsistent readings. I then bought a digital probe thermometer at Wally World that has a silicon sheath over the cable. I've checked it in ice water and boiling water and it seems to be accurate.

Yesterday, I stirred the heck out of my mash, threw the probe into the center of the mash and got a reading of 144. My strike temp was supposed to be 152. I stirred some more and the temp started to rise. I closed the lid and watched the temp rise over the next 5 minutes to 150.4 and said, "good enough". Over the next 20 minutes or so it dropped to 148.8 and held there for the rest of the hour. I stirred the mash to check for conversion and the temp quickly rose to 153.

This is typical for me, and all I can say about my mash temps is that they've been somewhere in the conversion range and that I've made beer. Since mash temp is key to getting the type of fermentables you desire, how can I determine what my mash temp is with any precision? Needless to say this is somewhat frustrating.

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Old 02-17-2008, 06:06 PM   #2
Teddi Brewski
Dec 2007
Tivertown, The Isle of Rhode
Posts: 72

Damn good question, I look forward to seeing this answered

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Old 02-17-2008, 06:12 PM   #3
Yuri_Rage's Avatar
Jul 2006
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I have a submersible temperature probe that stays in the mash during the entire process. I move it around and average several readings when I want to know exactly how the mash is doing.
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Old 02-17-2008, 06:27 PM   #4
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Feb 2008
Amherst, Western New York
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i think ome of the programs has a strike temp calculator. based on the #grain and the needed mash temp it calculates the strike temp water that will needed to be added.
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Old 02-17-2008, 07:36 PM   #5
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SenorWanderer's Avatar
Aug 2007
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what type of mash tun are you using? i use coolers and this is typical for coolers, but there are a few things you can do to help. are you pre-heating your mash tun with hot water? the insulation in a cooler can absorb quite a bit of heat. i typically fill my mash tun with near boiling water and let it cool to my strike water temp with the lid on. my strike water temp is usually around 170F. i use the calculator in beersmith to figure this out. you can also define a handful of variables in the program like how much it weights and what it's made of. this helps the program better gauge what temp you need. the other thing to consider is when you pour 70F grain into 170F water there is going to be a lot of temp variability for a while. i add 2 degrees to my calculated strike water temp and stir the mash until i settle into that temp. you're going to have to stir the mash anyway, and stirring the mash will cause heat loss. after my mash has settled in i can come back in 20 minutes and the middle of the mash is still at my desired mash temp, but the mash along the wall of the cooler could be 3F-4F lower. you can't really do too much about this besides further insulating your tun. i haven't decided whether it's better to stir, which will lower the temp everywhere, or to leave it so at least the core of your mash is at your desired temp. i think the most important thing to think about regarding mash temps (like most things in brewing) is to find a system that works and stick to it; be consistent. as long as you have a system that gets you to a starting mash temp you want, and then you do the same things to maintain that mash temp (or not) every time then you'll have the ability to make a consistent beer.

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Old 02-17-2008, 08:22 PM   #6
big supper
Jul 2007
Montreal, Quebec
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I too have had issues with this. I have been using a instant-read digital thermometer. near the end of the mash, I took a couple of readings, and it was reading low(around 146). Since the hour was pretty much up, we decided to go ahead and lauter. I took a reading of some of the first runnings and was suprised to see the temp at 152. What is up with that? I guess that I need a thermometer that will go deeper or something.

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Old 02-17-2008, 08:34 PM   #7
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Aug 2006
Whitehouse Station, NJ
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I know it's hard to get an exact reading. I've found that it really helps NOT to measure the temp until you've fully stirred well and let the grain pull in the heat from the strike water. If you're in a pocket of water, it will read high and if it's touching grain, it will read low. Close the lid for 5 minutes, let things stabilize, then go measure the temp. I like to lightly stir the mash with my instant read digital so that I'm getting more of an average rather than a pinpoint.
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Old 02-17-2008, 09:07 PM   #8
Aug 2007
Milford, CT
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This is a good question. Thanks IowaStateFan, I wondered about this myself. I always go by the reading in the middle with my digital probe thermometer. The sides are a little lower.

I shot for a high temp of 158 degrees with beersmith and it worked well on both of my PMs so far. I was right on on the first PM and at 157 on the second one. So according to my setup and beersmith, the middle seems to be the temp to take.

I guess your mash can't all be one temp. It'd be nice to know the exact layout of the temps in the mash. for instance...

15% at 157
30% at 156
35% at 155
20% at 154

I'd bet more mash is at the outside (lower) temps than the inside (higher) temps cause the outer area is larger. Just take the temps in the same places and make them work for you.
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Old 02-17-2008, 09:25 PM   #9
Sep 2007
San Jose, CA
Posts: 63
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Have you ever been swimming in a lake in the summer, and all of a sudden you swim past a nice warm spot? But then 5 feet later you hit a freezing cold spot? The point I'm making is that even pure liquids can develop hot/cold spots. It makes sense that a mixture (mash) with such high viscosity would behave the same way. I'm guessing if a speed boat zoomed through those hot spots, the lake would have a more consistent temperature in that area.

Try giving your mash a good stir. I watched AG video series (see the sticky threads in this forum) where (Yuri?) had a paint stir on the end of a drill - I'd imagine this does a pretty good job of distributing the heat in the mash tun.

I'd also imagine that even the digital thermometers aren't perfectly accurate... maybe something like +/- 2 degrees - so a 4-5 degree fluctuation might be right in line with the tolerance of the thermometer.

So my two cents: So stir it up well, and take the average of a few measurements.

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Old 02-17-2008, 09:52 PM   #10
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Jun 2007
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I have a probe through a thermothingy into a keggle, but found this to be too unreliable. Now, I just use it as a guide and use a calibrated Taylor bi-metallic analog probe thermometer at a few different locations in the mash. I calibrate it nearly every brew, but usually find it dead on. I just don't like the fact that the digitals (all the ones I've seen) aren't calibratable.

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