Help with direct heating mash tun

I’m using a direct heated converted keg as a mash tun and usually do single infusion mashes so there is no need to add heat. However, when I try to do a step mash or just try to hold temp, I’m having a hard time getting the temp up even just a few degrees. I’m using a false bottom and pump to recirculate.
The last time I tried a step mash I used rice hulls to improve flow and a 1.5qt/lb ratio. I also continuously moved the discharge hose around the top couple of inches of the mash to insure even distribution and occasionally stirred the mash being sure not to disturb the very bottom. The flow was good (almost fully opened valve) but the temps were very uneven through the mash. Using a thermopen I was getting wort readings from the discharge hose around 152 while the top of the mash was averaging 148 and my Brewmometer (mounted about 1/3 of the way up of the tun) was 144. Ambient temp was around 50. I could easily raise the discharge temp but the Brewmometer would not budge (even after 20 minutes or more of recirc and heat) unless I were to overheat the wort.
So my questions are:

  1. Are there any suggestions on how to get more consistent temps through out the mash?
  2. Should I be concerned about over heating the wort to raise mash temp?

Thanks for your help.

I used direct heat via a hot plate on several of my first AG brews, and then switched to a HERMS. I can’t really say that either one is better.

A Sanke keg’s dimensions are 15" wide by 23" tall. Of this space approximately 15" X 15" will be occupied by the mash (for a 10 gallon batch). A recirculated mash is subject to two hydrodynamic factors: Plug flow and wall flow. Wall flow is where the majority of the recirculated mash goes down the walls, and plug flow is where the majority of the flow goes down the center.  Most of the heat will be lost through the walls of the keggle, so we would expect that the outside would be cooler than the center, and indeed this is my experience.

I measure temperature in my keggle HERMS rig at three points:

  1. A 6" thermocouple half way down the keggle.
  2. A 2" analog thermometer a couple of inches lower than the thermocouple.
  3. A thermocouple at the exit of the HERMS coil.

The 6" thermocouple in the mash tun always reads a couple of degrees higher than the analog thermometer, and I believe that this is due to it being closer to the center of the mash.

What helps keep the temperature even throughout the mash?

  1. An insulating blanket for the outside of the mash tun.
  2. Almost constant recirculation through the HERMS.

I think that a mash mixer (like we had at the production brewery) would help, but I have spent years thinking about it, and totally failed to envision one for a 10 gallon keggle rig!

Charlie

Thanks Charlie.

I figured I’m losing heat through the tun walls and have been dragging my feet on the insulation but that’s probably going to be the next step.

A good way to insulate the keggle is to go too a big box store like Lowes and purchase duct insulation.  It comes in a roll and has a sticky sponge backing that will adhere to the keggle. The outside is basically aluminum foil.  I put several layers around the keggle and that helps keep the heat in and reduce the cooling around the walls of the keggle.  I use that in my brew system for the HLT and the mash tun.  It works well and my temps remain constant.

I have a RIMS system and a burner under the keggle to assist in heating the mash more quickly when doing a step mash or a mashout.  I can heat the mash from 152 to 168 in about 5 to 10 minutes.  I keep the recirc going while heating with both the RIMS heater and the burner to avoid scorching the wort.

I use reflective ‘bubble wrap’ style insulation wrapped around my induction fired boil kettle.

Thanks everyone. Looks like I’ll be shopping for insulation.

One name for the aluminized bubble insulation is Reflectix.

Even with insulation, you’re not likely to have a completely consistent temperature. I would suggest stirring the mash periodically. There is no harm in doing so. You also need to make sure that you are pulling wort off the bottom at a pretty slow rate. If you pull too fast, you will compress the grain bed and can introduce channeling as the wort tries to find an easy path to get to the bottom. when I use my HERMS, I watch the temp coming out of the mash tun and don’t let the wort that is coming back in to the tun go above 170. You lose a fair amount of heat going through the pump and lines, so even if you’re pulling substantially warmer wort off the bottom, it should cool a few degrees when it goes through the pump and lines.

I read on one of the brew forums that the ideal recirculation rate was 1 GPM. If your pump rate is higher than that you can use a Variac (variable transformer) to reduce its speed. And I did that for a while, but what I ended up doing was using 1/4 inch ID copper for the HERMS coil, and that reduced the flow to slightly less than 1 GPM without the Variac. Anyway, the 1 GPM rate seems to work for me.

Charlie

Will direct heat affect the bubble insulation? I think I’ve heard that on other threads.

My last batch I definitely was pumping more than 1 GPM. I wasn’t worried about channeling so much since a lot of rice hulls in the mash (10% of the grist). My other concern is overheating the wort. If a mash out at 170 stops enzymatic activity, isn’t that what you’re doing when you heat wort over that temp?

I once, quite by accident, hit 165F on mash in. Although I cooled it down quick the beer was undrinkably sweet, and that’s the only brew out of the 180 or so I have made that went right down the drain. So 170 F is definitely going to mess things up.

Try putting a short (6 inches or so) section of 1/4 inch copper tubing in the line and see what it does to your flow rate.

Charlie

In operationg a lauter tun, the metric that matters is not flow rate, but velocity – not gallons per minute, but inches per minute  – in order to establish the proper flow to avoid channeling or compaction and to optimize permeability and diffusion.  The relationship of velocity and flow rate will vary widely depending on the geometry (surface area) and loading of your tun, so there can’t be said to be an ideal flow rate.  The same principles will apply to a recirculating mash system as well, since that is essentially a continuous lautering operation.  This article specifically addresses conventional lautering process, but clearly outlines the principles and fundamental calculations and might give you some idea of how to calibrate your flow, or at least issues investigate further.  brewlikeapro.net

I haven’t ever measured the flow rate, but I shoot for between 45-60 minutes lauter time.  When I recirc, I try to achieve a similar flow rate to lautering. Once you know what that flow looks like coming off the mash tun, you can eyeball it.  The easiest way I’ve found to achieve this flow rate when recirculating it is to use a wort grant.  You can use a kitchen pot, even. Basically, you lauter in to the grant, then pump from the grant back in to the mash tun.  You will likely need to keep adjusting the flow rate to avoid the grant emptying, but you are assured of the correct flow this way. If you want to get fancy, you can make a grant out of a stainless 2 or 3 gallon kettle and add a port near the bottom for the outlet and an inlet port in the lid.

That was an interesting read and aligns so well with my experiences.  I start with a very slow recirc rate then increase it a bit as the mash thins with temperature through a Hochkurz mashing regimen (BIAB HERMS).  I have had noticeable bed compression from too fine of a crush and with too high of an initial rate (velocity, essentially in my situation) and have used rice hulls, mid-mash stirring and throttling flow.  The throttling of the flow has worked the best and most consistent for me.

Meh. I’m too lazy to do the math, and one GPM works for me. :wink:

Charlie

I, too, established my flow rate (I use a lauter tun) by long time experience teaching me what works.  Then I ran all the calculations from the article and found out… I was dead nuts on the perfect velocity.  So that kind of proves (in a bass ackwards way) the validity of the formulas and theories, which means if somebody’s having trouble, they should get them to a solution faster than trial and error.  But yeah, Charlie, those of us who lucked into it really don’t need to hurt our brains with extra math!

If direct heat means an open flame source — yes it will melt and even possibly ignite. Either way it’s gonna smell like @$$. If direct heat means electric coil — less of a problem (don’t let it touch).  Induction — no problem.

FWIW — my recirculating mash combination sweet spot is 5/16” on a pump output linear flow control valve (which is ~.7 gpm), a 1.75 qt/lb mash thickness, and a course crush where the kernels are broken into grits vs flour (.040 at the center of a JSP two roller mill).

I found it interesting that Mecca Grade recommendation for their malt is to “achieve the best possible extract and flavor, please consider using at least a .040” mill setting to maintain a fine crush on our malt.

No whole kernels

All kernels broken into at least three pieces

Starch exposure is critical”

I appreciate all the input on this subject.
It is open flame direct heat so any insulation will have to contend with that. In previous brews I have used a slower flow (not sure of the rate) with less than great results. Either the heat loss through the hoses, pumps and mash tun does not raise temps or the wort temp rises (190s +) under the false bottom and boils the wort which really restricts flow.

As I said in the original post, ambient temp has been around 50 in my garage and even when doing a single mash no recirc my temps are falling 8 degrees in a 60 minute mash. Thats with covering the lid of the tun with a blanket and covering the entire mash tun past the bottom with a flannel lined sleeping bag. The weird thing is, I used to use this method when I lived in Wisconsin and wouldn’t lose more than 4 degrees during winter months. And thats with removing everything and stirring the mash every 15 minutes.

I did increase the coarseness of my grind just a bit to improve flow but did not lose efficiency which is at 75%.

BTW how do you measure crush on your mill? I use a 2 roller Monster Mill.

Measure the gap on your mill using feeler gauges from the auto parts store, about $6 for a set.  I have the MM2 Pro with the 2" rollers and set it to 0.032" with good results, but that means little as you need to optimize the crush for your rig.

If you’re having heat loss in the hoses, you could try wrapping them with foam pipe insulation.