Mash Temp Regulation

Does anyone else have difficulty with this? I'm using a Coleman Xtreme cooler, and the issue isn't with keeping temp up once it's stabilized, but for some reason, I'm having some difficulty figuring out how to accurately hit my desired mash temp...

I've only on my 3rd AG batch, and maybe I just don't have my system dialed in yet...today, as an example, I calculated my strike temp as 176*F (based on the grain temp of 64*F, which is the temp in my garage where the grain has been stored for > 24 hrs, and 14.5 lbs of grain) The temp seemed to stabilize at 160*F rather than the desired temp of 155*F After stirring the mash with the tun open for about 15 min, I became concerned that it wasn't starting to cool off very fast, so I added some cold water, but then I undershot, and ended up at 148*F.

I've made a practice of pre-heating the cooler with the hottest water from my tap (presumably a fixed value as I've not changed the water temp on my hot water heater). I figured this would make my tun's thermal mass relatively stable from batch to batch...How do you actually calculate the thermal mass?

Does the ambient temp have much of a role? On my other batches I've had more of an issue with coming in a little *under* where I wanted to be (never off by as big of a difference as today). Both of the other batches were brewed when it was a bit colder out...

I use software and always hit mine fine. Heat water a bit above your mash in temp..let the temp drop to your mash in temp. Mix and than wait 10 minutes, re mix and check temp. It takes a few minutes for the mash to settle..so if you check them temp right after you mix the grain in you will get a range of temps..mix and wait and recheck in 5 to 10 minutes. If you continue to be 5 degrees above your mash than just adjust your intitial temp to hit your target.

I had that problem using a cooler that was only 1/2 full. Went to a 5 gal igloo and can hold with in 1 degree for 90 min. It's filled to the very top with 11 pounds of grain.

I use a 52qt Coleman Xtreme as a mash tun, and I use Beersmith Software. I have all of my equipment set up in the program, and when taking the grain temp and tun temp into consideration, BS gives me a extremely close strike water temp. However, I do heat my water up about 5° hotter than what BS says before adding it to my MLT.

As asn example, if my strike water temp from BS is 167°f, then I'll heat up to around 172°f-ish, I pour all of my strike water into the MLT, close the lid, and let it sit for about 10 minutes before doughing in. When I add my grain, I dump it all in at once, and stir, stir, stir for 5-10 minutes ensuring any doughballs are eliminated.

Taking your example into consideration, I think that preheating your MLT with the hottest tap water available, may not be the best way to go about it. If your tap water temp is much cooler than your actual strike water temp, then your MLT will still be sucking some of the heat out of your strike water before equilibrium occurs. And it seems like a waste of water, unless you are using that tap water for something productive afterwards . If you just heat up your strike water as normal, make it a little hotter than what your calculations say, allow your tun to preheat for bout 5-10minutes befoer doughing in, I think you'll be okay.

Take note though, the strike temp (IMO) givres you some leeway to stir, obviously there will be some heat loss as you are breaking up doughballs and ensuring your mash is thoroughly infused.

Ambient temps may play a small role in how much heat you lose over the 60 minute mash, but I think with the Coleman Extreme coolers it is anegligible amount, when ambient is ~80°f I don't even lose a degree, but when it is chilly outside, or really breezy, it seems like I can lose about a degree over the hour.

Stirring is the best way to cool off your mash, by bringing the hot part of the mash from the bottom of the tunto the top to dissipate heat, and gently stirring the top after doing so, it may take a few minutes, but it has worked well for me when I am a few degrees over. Adding water can be tricky because of the volume it takes to actually drop the temperature, and it creates cool spots when not thoroughly mixed.

Jbt said:

I had that problem using a cooler that was only 1/2 full. Went to a 5 gal igloo and can hold with in 1 degree for 90 min. It's filled to the very top with 11 pounds of grain.

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While this may seem like a solution, I'm not buying it. I call it coincedence, and more likely that the new cooler insulated better.

I use a coleman xtreme 72qt cooler. Rarely do i have it filled above halfway. I usually hit my mash temps dead on. Here's a trick: Preheat the tun. I fill my MLT with the hottest tap water while I am setting up my brewing and keep it closed. Once I am ready, I empty the tap water and keep the tun shut until its time to dough in. Also, I use a calculator that takes the grain temp and target mash temp into account and tells me what temp whatever volume i have needs to be. (Brewzor calculator app for androids)

NuclearRich said:

While this may seem like a solution, I'm not buying it. I call it coincedence, and more likely that the new cooler insulated better.

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This maybe. I'm not arguing the point was just my experience.
I also have a 52qt extreme. I made about 30 batches with the 52qt and probably about 12 with the 5gal. And I can tell you from my experience that in "my process" the 5gal was effortless to hold temp..

I also heat my strike water about 8-10 degrees above my strike temp, pour it into the tun and close the lid for 15min. Then I open it up and stir until I reach strike temp then dough in.


Schnitzengiggle Great explanation!! :rockin:

Thank you all for the replies...

@ Schnitzengiggle -- I think that I may start foregoing the pre-heating step, but not for the exact reasons you suggest. I'm sure that if my tun is cooler than the hot water, I'll be pulling less heat out of the strike water than I would otherwise (especially if the tun was on my deck at 45*F like it was the night before last!). If stirring is the best way to cool the temp, it sure seems slow! It seemed to me that the Coleman Xtreme was so efficient at holding heat, that even with the lid open, and me actively stirring for a full 15 min, the temp was holding rock solid at 160*F! I definitely started freaking out a little, and that's when I added the cold water...I added a little, and it dropped to 157*, a little more (about the same amount) and it plummeted to 148*F...

@NuclearRich -- I think I may start doing what you and Schnitzengiggle suggest, and putting the strike water in to the tun a little hot, stirring to get the strike temp where it needs to be, then adding the grain to it. At risk of introducing a separate debate to the thread, I had been putting all the grain in, then adding the strike water. I have seen other threads debating this issue, and from what I can tell, there's no hard reason why one way or the other should be considered best practice...I think in my case though, going to the water first way may help me learn how to regulate my tun's temperatures.

@Jbt -- I agree that the issue is not the holding temp part...It's just getting the right temp to hold! Once I equalize to a given temp, the cooler is rock solid at keeping that temp for the full duration of the mash.

I brewed this winter in temps close to freezing, so the ambient temps are as close to being able to affect my temps as possible. However, the MLT held strong. When I first started the all-grain process, it took some dialing in for "my process", which it probably will for you as well. Give your thermometer a couple minutes to equalize (as well as the temps in your mash to equalize after your dough-in); I found that the temps swing widely if you are too nervous and keep checking it.
Brewing software has really helped me, because it makes calculating the temps really easy and takes into account the temp of the grain (15lbs of 45dF vs 9lbs of 70dF grain makes a difference). Even with these calculations, I still felt like I was undershooting the mash temps by a few degrees, so I figured it was from the MLT temp and took that into account by preheating the tun.
All of this was made possible by the great notes and advice found within the pages of these books we call HBT threads.
Good luck, I am sure you will dial it in sooner than later.

NuclearRich said:

... it took some dialing in for "my process", which it probably will for you as well.

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This is what I figured...

NuclearRich said:

Give your thermometer a couple minutes to equalize (as well as the temps in your mash to equalize after your dough-in); I found that the temps swing widely if you are too nervous and keep checking it.

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Yes, the nervous factor is there...which is why I freaked out and added water (twice...) I think I'm going to invest in a digital thermometer recommended on another thread so I can get a more instantaneous reading, and also not have to open the tun to get a reading.

NuclearRich said:

Brewing software has really helped me, because it makes calculating the temps really easy and takes into account the temp of the grain (15lbs of 45dF vs 9lbs of 70dF grain makes a difference). Even with these calculations, I still felt like I was undershooting the mash temps by a few degrees, so I figured it was from the MLT temp and took that into account by preheating the tun.

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I do use software (ProMash), and I agree it's way easier...I'm still planning on trying to figure out how to calculate a better number/correction factor for my tun's thermal mass. I think once I get a different thermometer, I'll also check to see how accurate my estimated grain temp has been....

biochemedic said:

This is what I figured...



Yes, the nervous factor is there...which is why I freaked out and added water (twice...) I think I'm going to invest in a digital thermometer recommended on another thread so I can get a more instantaneous reading, and also not have to open the tun to get a reading.

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That's an awesome price... it seems to have at least a few positive reviews here based on the searching I did. I struggle with mash temps as well, and I'm going back and forth on ordering something like this or just biting the bullet and picking up a Thermapen. I'd love to hear your thoughts if/when you get this, particularly in the construction of the probe.

Preheating the cooler seems to work well for me.

I have a 48Qt igloo and i usually add about 4-5 gallons of 190' water while I set up and mill my grain, usually 10-15 minutes.

I use Beersmith and I heat the water up about 3-5 degrees above what BS says. Usually hit my target temps no problem, and it stays for the full hour usually. sometimes it drops a degree or two by the end of the hour.

I dont preheat but go 10* over what BS says and ive been. hitting perfect. Sometimes a degree or high so after doughing in i give it a good stir and wait. I have a digi therm with a probe in the cooler lid closed. After 10 i check and stir if needed. Usually im within a degree above and happy. I use a coleman 48qt. My cooler is in the spare bedroom so its always at house temp. Never cold on the porch or garage like a few of you. Brewzor on the droid is excellent for calculations on the fly.

So, first chance I've had to brew since this last batch was this morning. I think I did pretty good with the advice here...

I "over heated" the water into the 170's, dumped into the mash tun, and let sit for 10 min. It dropped 8 degrees to 170*F. (I'm going to track this number vs the ambient temp to get a better idea of the thermal mass of my tun...) I stirred until the water reached my desired strike temp (162*F). Added the grain and when things settled, I hit 150*F! Now, my target was 152*F, but this is still a far sight better than what was happening to me before! I think I just need to take into account temperature losses while actually doughing in, and add 2 degrees to my strike temps -- next time I should be able to nail it dead on!

Thanks all for the help!!!

I know this is an old thread but I was wondering how your mashing is coming along biochemedic. I have learned a few tricks from this thread and plan on heating my mash tun for around 15 minutes prior to adding grains. For example, I will put my strike water in at around 180 and let the cooler absorb the heat. Open the top and let the temp come down to around 165-168 because I want to add the grains and stir for a few minutes until I hit my mash temp at 154.

I was also considering adding a styrofoam top on the grain bed because I mash in a 10 gallon cooler and I'll probably only use half that. I'll probably add a layer of aluminum foil between the foam and mash just in case something wierd happens. Any thoughts?

pharaohpierre said:

I know this is an old thread but I was wondering how your mashing is coming along biochemedic. I have learned a few tricks from this thread and plan on heating my mash tun for around 15 minutes prior to adding grains. For example, I will put my strike water in at around 180 and let the cooler absorb the heat. Open the top and let the temp come down to around 165-168 because I want to add the grains and stir for a few minutes until I hit my mash temp at 154.

I was also considering adding a styrofoam top on the grain bed because I mash in a 10 gallon cooler and I'll probably only use half that. I'll probably add a layer of aluminum foil between the foam and mash just in case something wierd happens. Any thoughts?

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You have it exactly right on the process. You may find you only need 5-10 minutes of preheat. Grain temp and mash tun temp make a difference. For example my grain and mash tun are at 68° in the summer and 64° in the winter so I have to make slight adjustments. But your understanding is spot on.

thanks for the input iaefebs. Tomorrow is brew day and I'm excited about trying out this new process and hope I nail it to within a degree or two after 60 minutes.

pharaohpierre said:

I know this is an old thread but I was wondering how your mashing is coming along biochemedic. I have learned a few tricks from this thread and plan on heating my mash tun for around 15 minutes prior to adding grains. For example, I will put my strike water in at around 180 and let the cooler absorb the heat. Open the top and let the temp come down to around 165-168 because I want to add the grains and stir for a few minutes until I hit my mash temp at 154.

I was also considering adding a styrofoam top on the grain bed because I mash in a 10 gallon cooler and I'll probably only use half that. I'll probably add a layer of aluminum foil between the foam and mash just in case something wierd happens. Any thoughts?

Click to expand...

Yeah, process is working great...I heat to about 10*F over my desired strike temp (calculated with software, taking into account my grain weight and temp, which I measure by sticking a digital meat temp probe way down in the center of the bag/bucket of grain). I put the strike water in the mash tun, close it for 10 min so everything can equilibrate then stir it until I get to about 2-4 degrees over my strike temp, then dough in. By the time I get all the grain in and mixed up well, I am usually at my mash temp, occasionally have to stir a bit more to get it where I want if the ambient temps are on the warmer side.

FWIW, I also have a bigger than needed cooler, and I don't worry about the extra air space...at least in my cooler (coleman xtreme 6) I never drop at all over an hour mash, even when it is 33*F in NC like it was today when I mashed in at 5:30 am! After nailing the mash temp, the cooler kept an even 156*F the whole time...

Thanks for the response biochemedic, if it worked for you and many others then it should work for me as well. If it doesn't then clearly I am the problem. I'll let you guys know in a few days how it turned out. I thought I was brewing tomorrow but of course something unnessarily stupid came up. Now brew day is hopefully this Saturday!!

Thanks for all the comments. We have done well over 200 batches and most of my practices are fairly solid. Currently we are trying to get our decoction draw practice understood. Thanks to this site, I know better that to try for anything better than 20% accuracy by volume.

Also, thanks to the clues laid down in this thread, I know that the thermal mass of the grain (barley, oats, corn, & rice) is the same and constant (within tolerance) . I have found tables on the Wikipedia that make the same claim for liquid water (freeze to boil). The hydrometers used in brewing consider a 1% variation in specific gravity a significant change. Also, the software seems to make the same assumptions regarding heat energy and thermal masses. So, now I know, that the goal is attainable.

For my strike water practice I would like to predict the amounts of boiling and chilled waters needed to make first step mash (beta amylase) as close to 18 qts as possible (that is my decoction baseline) for the alpha amylase rest. It is probably more logical to begin with the initial strike, but the decoction has caused many more problems (squeaky wheel and all that).

Well, I brewed with the cooler today and it worked real well (almost too well). I had initially added about 180F water and put the lid on for 10 minutes. I opened it up and the temperature was around 170F. It was amazing to me how well it held at 170F. I was standing there for like 8 minute waiting for the water to get down to around 164F so I could throw my grains in there. After I put the grains in, I mashed for around an hour and lost about 2 degrees. Overall, a better performance than I expected.

Thanks for the posts everyone.