Author Topic: Mash bed temp  (Read 2233 times)

Offline benamcg

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Mash bed temp
« on: October 23, 2011, 07:39:09 AM »
Today I had to adjust the mash bed with cool water since the strike was a little hotter than usual (mash bed at t=0 was 160 F).  A while ago I had some issues with the standard lab thermometers (3 thermometers were giving me vastly different readings) so I bought a digital thermometer probe.  The probe is nice since I can monitor different depths of the mash bed. However, today I noticed that I was getting readings between 160 and 140 F depending on the bed.  I stirred the bed on multiple occasions (more than I would like), sealed the tun and waited.  I figured that the bed would adjust to a semi-uniform temperature.  45 mins in right now and it hasnt.  The variability improved somewhat (143-156).  I had never noticed this before, but might have been because I used lab thermometers which cant be buried to different depths while giving a reading. 

So my question is, is there is inherent variability in the mash bed (other specifics: rubber maid cooler, 30 lbs of malt), or is this an effect of fiddling with the strike water.  If there is the inherent problem with differences in the mash bed temp, do you measure temp from a specific location or depth (e.g. middle of the tun, 4" deep) or do you look for an average temp across your measurements to fall into the 150-155 range?   I would imagine that the size (lbs of malt) and shape of the container matter too.

Offline mabrungard

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Re: Mash bed temp
« Reply #1 on: October 23, 2011, 09:12:09 AM »
You substituted a potentially incorrect digital temperature probe to replace obviously incorrect thermometers?  You still have not solved your problem.  You need a verified reference thermometer and the rest of the thermometers need to be adjusted or corrected to that standard. 

This has been a recommendation of mine for some time:  Every homebrew club should have a reference thermometer somewhere in its ranks.  That reference thermometer should be brought to the club's meetings and events so that the members can compare their working thermometers to the reference occasionally.  All that is needed is an insulated vessel with hot water (preferably in the 150F range).  That way, members have the opportunity to find out and correct errors in their temperature measuring capability.   

Temperature measurement is a critical component in brewing.  Just because you have checked your thermometer at freezing and boiling, does not mean that its reading correctly at the more important mashing temperature range. 

Using an electronic instrument does not mean its more accurate than a analog instrument!
 
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Re: Mash bed temp
« Reply #2 on: October 23, 2011, 09:39:10 AM »
So my question is, is there is inherent variability in the mash bed (other specifics: rubber maid cooler, 30 lbs of malt), or is this an effect of fiddling with the strike water.

I think it's probably the result of not stirring enough. I stir for 2-3 minutes, continuously, making sure to move the mash around in all three axes, before the temperature is more or less uniform.
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Re: Mash bed temp
« Reply #3 on: October 23, 2011, 09:56:06 AM »
Besides Martin's great advice, I'm agree with the not stirring enough.  You need to keep stirring until you get the same reading (or very nearly so) at every place and depth in your mash tun.  It's not the amount of time, it's the results that should determine when you've stirred enough.
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Offline benamcg

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Re: Mash bed temp
« Reply #4 on: October 23, 2011, 10:02:45 AM »
I totally agree that temperature is critical (I have a friend who all grain brews and yet never takes a temp - he tells me I worry too much!).  As far as calibration I also agree that a 150 calibration would be ideal.  It does seem to be accurate with the lower temps that  can calibrate against.  All I have for calibration purposes are using a sealed container (beaker with plastic wrap) in an environmental chambers at work (75-80 F) or the chest freezer (35 F).  Again, not ideal.  I always thought analog thermometers were fool proof.  I am still puzzled as how three thermometers could have a range of 20 degrees around the 150 mark?

I also agree with the other post that it might not be enough stirring to uniformly distribute the temp.  I think next time I will be more careful with the strike water and avoid having to stir.

As far as whats in the kettle> after recirc. it was flowing clear with 75% efficiency.  Maybe I do worry too much.  I just want to make consistent beers....

Offline maxieboy

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Re: Mash bed temp
« Reply #5 on: October 23, 2011, 10:08:30 AM »
+ 1 on the thermometer advice and stirring. I like to calculate my strike to mash in a degree or two above my target. This ensures the mash is thoroughly mixed because of the amount of stirring required to lose that degree or two.
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Offline andyi

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Re: Mash bed temp
« Reply #6 on: October 23, 2011, 02:19:56 PM »

I agree you stir as long as it takes.  Also, I use a minimum 1.5/1lb mash that creates a consistent mash bek temp fairly quickly.

@Martin

Any suggestions for  analog  reference thermometers. Homebrew shops label the  $8 generic glass thermometers (with mecury or whatever) as "lab" grade.   

Offline mabrungard

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Re: Mash bed temp
« Reply #7 on: October 23, 2011, 03:01:41 PM »
I picked up a NIST certified reference thermometer off of eBay many years ago.  I don't remember the price, but as with all things on eBay, waiting and watching will reward you.
 
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Offline boapiu

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Re: Mash bed temp
« Reply #8 on: October 24, 2011, 05:20:57 AM »

I agree you stir as long as it takes.  Also, I use a minimum 1.5/1lb mash that creates a consistent mash bek temp fairly quickly.

@Martin

Any suggestions for  analog  reference thermometers. Homebrew shops label the  $8 generic glass thermometers (with mecury or whatever) as "lab" grade.   

I was considering one of these. You might take a look at the "gear" forum.

http://vwrlabshop.com/vwr-lollipop-thermometers/p/0025608/
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Offline andyi

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Re: Mash bed temp
« Reply #9 on: October 24, 2011, 01:03:24 PM »


Thanks Martin


@boapiu

I have this same lollipop thermometer.  The probe length (heh) is great for getting into the mash bed but....

When the readout is to close to the mash surface the steam will cause it to blank out for a time.  I suggest keeping the readout at least four inches above the mash surface

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Re: Mash bed temp
« Reply #10 on: October 24, 2011, 01:39:14 PM »
I have this same lollipop thermometer.  The probe length (heh) is great for getting into the mash bed but....

When the readout is to close to the mash surface the steam will cause it to blank out for a time.  I suggest keeping the readout at least four inches above the mash surface

I don't use mine for the actual brewing.  I use it to calibrate the bimetal dial thermometer I use for brewing.
« Last Edit: October 24, 2011, 01:56:41 PM by dbeechum »
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Offline davidgzach

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Re: Mash bed temp
« Reply #11 on: October 25, 2011, 05:33:34 AM »
Good advice here, thanks.
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Offline beerdoc

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Re: Mash bed temp
« Reply #12 on: October 25, 2011, 06:51:34 PM »
In my experience, it is difficult to get a uniform temperature in a stiff mash with any  reasonable amount of stirring. Another concern is  that some thermometers are sensitive to the extent of immersion. One thing to watch out for in any type of electrical probe is that the actual temperature sensor is not always at the tip. So you may sometimes have the probe out of the mash without knowing it. With all that, the real issue is that there is that usually some stratification of the temperature, so if your thermometer is reasonably fast and easy to move, you will pick that up. Best not to worry too much; bad for the spleen and liver.

Offline phunhog

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Re: Mash bed temp
« Reply #13 on: October 29, 2011, 05:23:36 PM »
Now how would this apply to a direct fired RIMS setup? Of course I stir when doughing in and recirculate after I get it all the grain in the mash tun. I like to compare my two thermometers. One is a bimetal and one is a floating. They read the same when I am heating my strike water. Once I start the mash though it isn't unusual to have a difference of 6-8 degrees F even after stirring/recirculating. I think part of my problem is that the probe on the bimetal doesn't go deep enough into the mash, only an inch or so, and it usually reads on the low end. I do wonder though how easy it is to get a truly uniform mash temp and what is the effect of mash temp variance. Do the enzymes care that some are at 150 and some are at 154? That is why I just shoot for a range of mash temps say 150-152 and call it good.

Offline bluesman

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Re: Mash bed temp
« Reply #14 on: October 29, 2011, 05:57:52 PM »
A NIST traceable thermometer is a desireable tool to have in one's toolbox. I have a lab grade thermometer that I use to calibrate my digital thermometer. I also have a Thermapen which is precalibrated and fast reading. A reliable thermometer is one of the most valuable tools a homebrewer can own.

I like to stir the mash until I reach the point when there is +/- 1 degree temp differential in the grain bed. At that point I will let the mash rest. I will check the mash temp again 30 min into the mash.
Ron Price