Mash temp increasing on its own?

What I'm describing below has been consistently happening for every batch I've brewed in the last year.

Why does the end temperature of my mash end up higher than the beginning temperature?

1. I have a 10 gallon round cooler (the typical orange type from Home Depot), with a false bottom, etc, which I use for mashing.
2. I take both the grains and the cooler out to the garage about two hours before mashing to let their temperature stabilize (I brew in the garage).
3. I measure the temperature of the grains and enter that into BrewSmith so it can figure out for me the initial temp of the mash water before putting it into the mash tun.
4. Five minutes after I put the water into the mash tun, I measure the temperature. Let's say it's 152F and it's where I want it to be.
5. 30 minutes into the mash, I measure the temperature again. Invariably, it's about 4F over the initial measurement and above where I wanted it to be. This temperature usually holds until the end, although sometimes it may be higher by a degree or two by the end.

What's going on? I figured five minutes of settle time should be plenty. And in any case, why would the temperature *increase* over time? If anything, I can see it decreasing. Enzimatic activity doesn't generate that much heat, if at all, does it?

This has me very, very puzzled.

 

Tough to say, but when I'm starting my mash, I usually end up overshooting temps by just a hair, so I end up stirring quite a bit until I hit my target temp. I think stirring gently helps equalize hot spots. Usually I will check multiple areas in my mash tun to get an average. My final (60 min) temps are typically either the exact same as start or sometimes 1 degree lower.

Are you using a probe thermometer?

 

I use a floating glass type of thermometer.

Maybe I'm not stirring enough. But my concern with stirring more is that the software calculated a specific temperature for the water given the current temperature of the grain and mash tun and their respective thermal mass. I could be letting too much heat go.

 

I always stir my mash before taking its temperature. This evens out the water temperature between the hotter water on top and the cooler water at the bottom.

 

You gotta stir it up good. No way around it unless you recirculate. The temp isn't rising on you, it just didn't get stabilized before you took your initial reading. Either that, or you didn't give the thermometer enough time to adjust before you read it.

 

Sorry guys, I don't think I was clear enough. I do stir the mash after putting in the water. I do it for a minute or two and try to mix it up well. The first temp reading I take, 5 minutes in, is after I've stirred the mash.

 

are you using the same thermometer for all the measurments?this seems odd.i used the same type of mash tun you are for quit a few batches and i always had an initial temp drop,hhmmmmmm.maybe you need a new thermometer?i used and still do for calibrating my probe therms the floating type/dairy therm and i have noticed that it does need a good amount of time to get an accurate reading.

 

Did you stir the mash before you took the temperature 30 minutes into the mash?

 

I do use the same thermometer for all mash temp measurements.

Indeed, if any change at all would be expected, it would be a temp drop.

Do you think the thermometer needs more than 5 minutes to level off? I put it in right after I stir the mash, close the mash tun, and then set the timer for 5 minutes. After I read it, I leave it in until the very end, so by the time I take the mid-point measurement (30 minutes or so), it's been sitting there for a good while.

The funny thing is that you'd expect the temp to be really high initially. So, if the water in temp is supposed to be 164F so it stabilizes at 148F (my last batch), you'd think the 5 minute reading may be something like 155F if I don't stir well, with a 30 minute reading below that. Instead, I get a 149F reading at 5 min and a 153F reading at 30!

 

No, I don't. Should I be?

 

yes

 

I'm thinking my initial reading is wrong. But could I be off by that much? And 5 minutes should be plenty of time to stabilize the reading.

 

Really? Stir the mash at mid-point? I don't doubt what you are saying, but have to admit I've never read or heard about this before...

 

Well, at this point, I suspect it's the thermometer. Get a good digital and throw out that crappy floater.

 

As your mash is sitting two things are happening. 1 the starch is turning to sugar which is heavier than water so it sinks to the bottom. 2 the water at the top is cooling and then sinks below the hotter water. Commercial brewers have paddles inside there mashtuns that slowly stir there mash. So by giving it a gentle stir you even out all your temperatures and you'll get a more accurate reading and it will boost your efficiency some.

 

Fair enough. I do have a digital thermometer, but while I'm mashing I use it to keep on top of the sparge water temperature. I can certainly use it for a quick mash temp check.

 

I wouldn't have a problem with doing some stirring at mid point. A concern would be losing heat, but since I'm "gaining" heat , maybe the loss won't be significant.

 

I think what you are gaining is heat differential within the mash. Measuring with a floating type thermometer only measures the top layer and heat rises. Stir bottom to top a few times then measure. Hell if its a round drinking water type cooler, screw the top on it and shake it if you are worried about heat loss.

 

Are you taking readings at multiple spots in your mash to start with? It takes a lot of thorough stirring to get consistent temps throughout the mash. Take 4-5 readings to begin with. You'll likely notice your temp variances here.

No need to stir mid mash. You're just letting heat out.

 

i agree with stirring mash throughout the process.you will not loose a signifigant amount of heat.i used to pre heat my cooler with hot water so i wouldnt have as much of a temp drop.now i use dirrect heat and resurculate and stir like crazy.

 

Stir it multiple times and check the temps each time. I had the same issue and just started to really give the mash a good stir a couple times a few minutes apart before I even took my first reading.

 

I've run into the same issue... Sometimes I've gotten a 4-5 F rise. Part of my problem was I had warmed my cooler a little too much, but have also found that I really don't stablize mash temps for almost a full 15min at times. I've started to get into the habit of stirring periodically for the first 15 min, focusing on bringing up grist from the bottom of the mash tun.

 

To close this up...

Today I made it a point to stir constantly for the first five minutes of the mash and to stir well. I then took a reading five minutes after that and 30 minutes later.

The temperatures this time were consistent. It was 152F (what I wanted) at ten minutes, 30, and 60.

What I'm taking away here is that I should stir well, a lot better than I was doing it. A good mixing stabilizes the temperatures and also brings them to the right level I want them.

Thanks everyone for all the posts and help. I'll make sure I post here again if my experience varies from this lesson.

 

Awesome!