Crazy-low mash temperature when making my pumpkin beer!

Hi,

I was brewing my Southern Tier Imperial Pumking clone today. My grain bill was:

14 lbs - Briess 2-row
3 lbs - Pumpkin puree
1 lbs - Caramel 80L
1 lbs - Rice hulls
Some crushed up graham crackers

Based on all my calculations, both in Brewtarget and on several websites, my strike temp should have been right around 170 to hit a mash of 156 (yes, mashing high). I transferred the strike water to my 10 gallon cooler and allowed it to warm the cooler for a few minutes.

I then added the 3 lbs of pumpkin puree (temperature 67~ degrees). I then added my grain and stirred vigorously. After 15 minutes, I returned to ensure I was hitting my mash temp. 146!!!!! WTF???? I thought my floating thermometer was wrong, so I grabbed another. Ditto.

How can this be? I only had the lid off for about 2 minutes to add the pumpkin and the grain. This makes no sense. I've never had trouble with hitting my mash temp before. If anything, I usually overshoot by a degree.

Any thoughts? I don't get it, unless I REALLY didn't read my HLT thermometer right when I transferred, but I really don't think that's the case.

Easy answer, but I can understand your dismay: 10° down... Now what?

The thermal mass of pumpkin puree is quite high. Do the calculators really have a "dense pulp" function built in?

I'm ready to brew a pumpkin ale and intend to just use the absolute minimum of spices, so it doesn't taste like pumpkin pie. Pumpkin has a very delicate flavor and I've made ice cream out of it. Without all the over-the-top spice it tastes really good. I'd like a pumpkin ale similar to that.

IslandLizard said:

Easy answer, but I can understand your dismay: 10° down... Now what?

The thermal mass of pumpkin puree is quite high. Do the calculators really have a "dense pulp" function built in?

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Haha, dense pulp function - that falls into the statistically improbable phrase category. I wish. I didn't think of that. Most "things" you can add have low density. Pumpkin is basically a big heat sink in the mash tun. I managed to adjust on the fly and still hit my target gravity, albeit at the sacrifice of some mouthfeel I would imagine. Now, the stuck lauter and sparge was a whole 'nother beast. I plan to brew this again in a few weeks. I think, based on my experience, I'm going to raise my strike temp about 10 degrees.

I did a pumpkin this afternoon also. My recipe called for the pumpkin to be cooked in the oven at 350 for an hour. I took it out and let it cool for about 15 min so mash temp wouldn't go crazy high. It still was 2 degrees hotter than I wanted.

And I also got a stuck sparge....

So I did some googling to find the thermal conductivity value for pumpkin. Some university physics course website in New Zealand had the value at .83 J/ m-1 s-1 deg. C -1, which is actually equivalent to the more standard Watts/m-1 deg K-1. That's really high, especially among the fruit and vegetable group (see here).

So, with Fourier's heat transfer law, you are looking at a very large temperature gradient and relatively high thermal conductivity compared to grain. Solutions --- overheat the water to compensate, or preheat the pumpkin puree to close to mash temperature. Both would reduce the temperature gradient, and subsequently, the thermal transfer.

waldzinator said:

So I did some googling to find the thermal conductivity value for pumpkin. Some university physics course website in New Zealand had the value at .83 J/ m-1 s-1 deg. C -1, which is actually equivalent to the more standard Watts/m-1 deg K-1. That's really high, especially among the fruit and vegetable group (see here).

So, with Fourier's heat transfer law, you are looking at a very large temperature gradient and relatively high thermal conductivity compared to grain. Solutions --- overheat the water to compensate, or preheat the pumpkin puree to close to mash temperature. Both would reduce the temperature gradient, and subsequently, the thermal transfer.

Click to expand...

The OP used pumpkin puree so the thermal conductivity of chunks of pumpkin is not the issue here. Rather it's the high specific heat of the pumpkin compared to grain that's the problem. It takes a lot of energy to warm up that three pounds which results in a lower mash temp.

BackAlley said:

The OP used pumpkin puree so the thermal conductivity of chunks of pumpkin is not the issue here. Rather it's the high specific heat of the pumpkin compared to grain that's the problem. It takes a lot of energy to warm up that three pounds which results in a lower mash temp.

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Agree. I was the OP. I was thinking of pumpkin chunks because that was my ideal situation --- I just couldn't find fresh pumpkins yet. But yeah, the specific heat of the pumpkin puree is the issue here.

Either way, both situations require adjusting either the strike water temperature of the starting temperature of the pumpkin.

I use brewtarget since I'm a Linux guy. Does any other brew software handle pumpkin and other popular fruit/vegetable adjuncts better? There was nothing in my fermentables category that I could add that even comes close to pumpkin in terms of conductivity or specific heat.

Maybe next time you could take the pumpkin puree, add it to a big bowl, add some water to it that is around 190 degrees stir it around, and then dump it all in.

waldzinator said:

Agree. I was the OP. I was thinking of pumpkin chunks because that was my ideal situation --- I just couldn't find fresh pumpkins yet. But yeah, the specific heat of the pumpkin puree is the issue here.

Either way, both situations require adjusting either the strike water temperature of the starting temperature of the pumpkin.

I use brewtarget since I'm a Linux guy. Does any other brew software handle pumpkin and other popular fruit/vegetable adjuncts better? There was nothing in my fermentables category that I could add that even comes close to pumpkin in terms of conductivity or specific heat.

Click to expand...

I would assume that the specific heat of pumpkin is about that of water. Therefore, you could treat the pumpkin as if it was additional water in your strike. Let's say the software said you needed 4g at 170F and you're using 3lb pumpkin (about 3/8 gallon) at a temperature of 70F. Your 3.625 gallons of strike water then would need to have a temperature of T:

3.625*T + 0.375*70 = 4*170

Therefore:

T = (4*170 - 0.375*70)/3.625 = 180.3F

Of course I could be totally wrong here but the results seem reasonable.

BackAlley said:

I would assume that the specific heat of pumpkin is about that of water. Therefore, you could treat the pumpkin as if it was additional water in your strike. Let's say the software said you needed 4g at 170F and you're using 3lb pumpkin (about 3/8 gallon) at a temperature of 70F. Your 3.625 gallons of strike water then would need to have a temperature of T:

3.625*T + 0.375*70 = 4*170

Therefore:

T = (4*170 - 0.375*70)/3.625 = 180.3F

Of course I could be totally wrong here but the results seem reasonable.

Click to expand...

One problem I'm running into is finding a good specific heat of pumpkin. So far, the only source I've found is the link above which indicates it is 3.97 kJ kg-1 degK -1. I believe this is somewhat less than water, right? Still, pretty close. So the algebra to me seems right. It also jives with the empirical data...I fell about 10 degF short.

Lots of crazy math going on in here...just do what I do in the future...add the puree to the strike water as you heat it up then add you grains at your proper strike temp. Usually end up a degree or two higher when the dust settles

Calichusetts said:

Lots of crazy math going on in here...just do what I do in the future...add the puree to the strike water as you heat it up then add you grains at your proper strike temp. Usually end up a degree or two higher when the dust settles

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Yeah, I just don't want to crap up my HLT. That's the one vessel that I don't have to clean religiously.

I would just heat the pumpkin puree to the correct mash temperature, or a bit higher, and then add it to the infused mash.

There's an article in this month's Zymurgy on pumpkin ale and they use a 10 minute protein rest at 120°F.

The biggest problem we have with cooler-type mash tuns is that we can't raise the temperature that easily except by adding more boiling water, often thinning the mash more than we want.

What I was thinking is to drain the wort in a pot and heat that up, carefully, not to exceed your next step's temperature or you're denaturing those target enzymes by the minute. That leaves the grain bed still at the lower temp, but then needs less boiling water to raise that. Then add the preheated wort. I can easily see why people resort to RIMS systems at some point. Or decoction mashes, if you have the time.

IslandLizard said:

I would just heat the pumpkin puree to the correct mash temperature, or a bit higher, and then add it to the infused mash.

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Agree. This is by far the easiest approach, though most ovens don't go that low so you would need to monitor it a bit and run the oven at the lower setting.

IslandLizard said:

I can easily see why people resort to RIMS systems at some point. Or decoction mashes, if you have the time.

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Amen. In the process of building a direct-fire mash right now. I have the arduino PID controller built, now I just need to cut up my keg and get some low pressure propane plumbing and furnace valve. Step mashing --- here I come.

IslandLizard said:

I would just heat the pumpkin puree to the correct mash temperature, or a bit higher, and then add it to the infused mash.

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Probably because I'm an engineer but to me running a couple of numbers in a simple equation feels easier than breaking out another pot, heating and stirring and measuring temps.

waldzinator said:

Yeah, I just don't want to crap up my HLT. That's the one vessel that I don't have to clean religiously.

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*faceslap*

Sorry for the ill-advice. I don't have a HLT, just a direct-fire mash tun I heat the strike up in.

waldzinator said:

Yeah, I just don't want to crap up my HLT. That's the one vessel that I don't have to clean religiously.

Click to expand...

You could probably just do what I mentioned and put the puree in a bowl and mix in some hot water in it, then put it in the mash tun. You could even microwave some water in a 1 - 2 quart pyrex and use that to mix with the pumpkin, instead of worrying about the strike water temperature.

Calichusetts said:

*faceslap*

Sorry for the ill-advice. I don't have a HLT, just a direct-fire mash tun I heat the strike up in.

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Do you do no-sparge, or do you have an alternative way to heat up your sparge water?

EDIT: I guess after further consideration, you probably heat the sparge water in the MT? Haha, if so, dunce cap for me! That probably adds a bit of time to your brew day, if that's the case, right?

waldzinator said:

Do you do no-sparge, or do you have an alternative way to heat up your sparge water?

EDIT: I guess after further consideration, you probably heat the sparge water in the MT? Haha, if so, dunce cap for me! That probably adds a bit of time to your brew day, if that's the case, right?

Click to expand...

I got another pot for my sparge water...I heat up the sparge just before I start my mash out. I pour the grains through a paint strainer in a colander into my kettle...do it back into the MT then to the kettle. I start boiling the wort while I add the sparge to my MT and repeat the process using the sparge pot and MT. Super ghetto but I hit 70% everytime...I hit 80% on a 12% barleywine and turned it into a monster. Super cheap and and no hassle with smaller batch sizes.

I bought I 5 gallon kettle..got the drilled hole and the kettle conversion kit. Even got a cooler and the conversion kit. They just sit in my basement never used as I see no need to change my system after several years, especially with the consistent results I get.

Calichusetts said:

They just sit in my basement never used as I see no need to change my system after several years, especially with the consistent results I get.

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It ain't broke, don't fix it!