Mash tun too big??

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Jun 10, 2023
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Hi, kids. I recently upgraded to a 20 gallon Ss Brewtech mash tun, and I'm having trouble maintaining mash temp. I normally do 10 gallon batches, but in the summer I will do an occasional 15 gallon. Has anyone else had trouble holding steady temps in a bigger MT? I can't apply heat like I could in my keggle tun, and have been using my HLT and a counterflow chiller to get the temp back up, but that's a pain in the neck. Should I just get a smaller mash tun?? I just realized that I posted this question before... Still, if anyone has any ideas.... Cheers!
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The vessel is insulated, which is why I can't add direct heat. I'm wondering if a 20 gallon tun is just too big for 10 gallon batches. I thought going larger would give me more options, but perhaps, like shoes, I need a better fit...
fwiw, I do 10 gallon batches on a 20 gallon mlt on a 3v2p herms rig and my 1.107 OG stout barely fits with maybe 2 inches of freeboard. I definitely would have problems using a 15 gallon mlt...

Are you using it outside, cold weather, wind?
Have you tried extra insulation around the tun, and on top of the lid? Such as 2 or 3 layers of Reflectix and/or some thick (moving) blankets or an old sleeping bag.

Also putting the tun on top of some (dense) styrofoam or a double or triple layer of those 1/2" thick foam rubber floor tiles.

For comparison, I use a 13 gallon plastic beverage cooler mostly for 5 or 6 gallon batches. So it's also only about half full. The walls are probably a good inch thick. I lose most heat while doughing in and 3-4 °F during the hour-long mash, so I start high when doughing in and when I reach my target mash temp (or a degree or 2 higher) I close the lid.

I brew indoors.
The lids on the SS Brewtech Infussions are already insulated, they float in fact! Just got one and need to alter it so I haven't brewed with it yet. Mine is the 10 gallon and will be part of a 3V2P EHerms, so it will hold temp since it will be recirculating. A suggestion from SS Brewtech is to "prime" the MT with hot water first. I wouldn't need to do that since I am using EHERMS so I didn't read carefully about the process. It is however on their website, I think in the MT Q&A section. I was thinking it was a wasteful idea as far as energy and water. There is also a document detailing how much grain one might expect to be able to fit in the unit.
Are you familiar with the product or are you thinking it is more of a pot? The OP didn't mention exactly that it is an Infussion, but given the mention of no heat application, I am reasonably confident that it is. My tight fitting insulated lid weighs 3.75 lbs and is SS on both sides. More insulation can help but it seems a pretty real lid. SS Brewtech also posts data for heat loss experiments they have done. Again, I'm not worried about that given my system but it did appear well insulated in general already as there wasn't much loss. I switched out an uninsulated keggle so certainly a big upgrade as far as holding in the heat!


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A suggestion from SS Brewtech is to "prime" the MT with hot water first.
I second the motion to preheat the MLT before mashing in. It might be as simple as experimenting to find out how many degrees the strike water temp drops after adding it to the MLT (and placing the lid) before stabilizing. Then add that many degrees to your strike water temp. Then when mashing in, let the strike water temp stabilize before adding the grain.

Brew on :mug:
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I second the motion to preheat the MLT before mashing in.

Brew on :mug:
I use a igloo cooler but even so I preheat to ~68 degrees. I mostly brew in the winter months so I'm mashing in the garage. Preheating in winter brings the vessel up to basement ambient and allows me to dial-in Beersmith as though I only brew in the basement which is much more temperature stable.
Pre-heating a mlt is helpful for establishing an initial condition. But the same endpoint can be accomplished with a strike temperature that accounts for equipment losses.

I plug grain and mlt temperatures into Beersmith3 and it tells me the strike temperature to use to hit my desired initial mash temperature (typically between 150 and 152°F). No preheating required...

Pre-heating a mlt is helpful for establishing an initial condition. But the same endpoint can be accomplished with a strike temperature that accounts for equipment losses.

This is true, and I would just clarify that you can get the strike water into the tun well in advance of the grain so you can let the tun take all the heat it wants. I also recommend either tilting the tun to expose the upper walls to the hot water as air is not a great conductor of heat. When the grain goes in, the displacement exposes the mash to the colder areas.
Those all sound like good suggestions. I only brewed with a cooler once so no tips from me on that score. I need to enlarge the upper port to fit my float valve, I got the bit today at least. I read a number of SsBrewtechs FAQs and literature on the mash tun but I was mainly looking for dimensions. I think they mentioned that the mash temp might drop ~4 degrees on an average batch? Not sure if that is the correct number and not sure what might be an equivalent cooler drop. Honestly I think its just a shiny cooler. I think it looks better than an insulated keggle. I got mine for a great price used.

Here's something though. Even though I haven't brewed with it yet, I did already go in to change my equipment profile in Beersmith 3. SS Brewtech suggested no deadspace loss and some small amount recoverable, which I entered but don't remember offhand. However, while I had the weight, I had no idea what the specific heat capacity might be as it is only partly stainless as well as the rest being insulation. Once I start brewing with it I think I will get a better idea if there is any bias in the equipment profile and hopefully a pattern may emerge.
@bobby_1 Another HBT member ordered a customized heating mat for theirs which they added to the bottom inside the removable bottom plate. There's a thread on it here.
Just to clarify on this, for the 20g you will want a bigger heat mat than the one I have listed for the 10g.

Before I had the heater deployed I found it essential to preheat the tun as it is a decently large thermal mass. I just would fill my my wife's electric tea kettle, get the water to a boil, and I found that about 1 kettle worth would get me fairly close.

Best of luck!
Are you preheating the mash tun?

Since it has such a large thermal mass, you need to soak it in hot tap water for about 30 before use and drain just before mashing in

Thats what I did with my 5 gallon one and it held like a champ
I have the 10G SS Brewtech MT. If you are basing your temp loss on what the included thermometer in the thermowell measures, then you may be off. For some reason, on mine, that one always dropped quickly.

I was using a RIMS tube and the temp of the liquid. running through the tube (unheated) was always warmer than that stupid thermometer on the front of the MT. I eventually just put a cap on that TC, so i didnt have to look at that off temp.

I’d open the lid on your next brew and stick it with a thermometer in a few places, just to make sure you’re not experiencing the same thing.
I read back what I wrote and wanted to clarify something. When you hear "pre-heat", I know a lot of people think of it as adding water to heat it up and then dump that out and start fresh with strike water. I don't know why anyone does that because it's a waste of water and time. Whatever your software says is the correct strike temp based on your grain amount and temp, add like 20F to that number. Put that in your mash tun, close the lid and let it soak for about 10 minutes. Open up the lid, tilt it to let the water touch all the sides, give it a stir until the water measures what the software wants. Stir the grain in. That is the BEST you can do without adding external heat sources.
Before I had a pump and RIMS, I’d preheat my SSBT 10G MT by heating 8-9gallons of water to strike temp. Then fill the MT. Let it soak for 10 minutes. Drain the excess water from the MT into my HLT, add the rest of the batch sparge volume of water to the HLT and start heating the HLT. Then I’d mash in.

If I measured temp by sticking the mash with a temp pen at the end of 60 minutes it held temp within a few degrees. Often temp within a couple of degrees. Measuring temp in the same way at the begging and end of mash. If however I measured temp with the SS Temp probe on the front of the MT it showed 5-7 Degree F drop over the same period. I even tried putting insulation round the TC fitting. Made not diff.

Even. with a RIMS and recirculating, the SSBT Temp probe ALWAYS showed a much greater temp drop. It read correct til grains were added. I brew in a 75-78F Garage.
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