The Mash Tun

by Michael Wood

This article is a description of the mash tun I designed for my brewery. I hope to write a series of articles on my brewery and its construction divided by the various stages of the brewery and I figured that mash tun is as good a place as any to start.

Before I started designing anything, I first went out and did research on the Internet and various book and magazines to see what others have developed. I also gleaned knowledge from talking with homebrewers such as the members of my homebrew club The Draught Board and various email correspondences through the Usenet and the Homebrew Digest mail list. I write this article in the spirit of those who have shared their brewery ideas for the good of everyone such as myself. I don’t represent my designs as the best possible but only as the one I adopted and why. I hope that I can share my ideas, failures and successes so that others might use this knowledge in their own efforts.

Before I started to design a mash tun, I wrote down a wish list:

Able to do step mashes

Large enough for #50 of grain

Stainless steel to prevent rust.

Low drain plug to collect the maximum liquor

Must double as a Lauter tun.

Easy to get temp measurements

It must be able to be insulated to keep temperature during starch conversion

Easy to construct with minimum effort

It has to be as safe as possible

In order to raise this much mash up in temperature, I decided it had to be direct fired. I wanted a true false bottom so that I could heat the mash without scorching the grain. One of the problems this method has is that the liquid under the mash tun doesn’t mix well with the solid grains above it. I figured that I could solve this by some sort of recirculation of the liquor from below the false bottom to the top of the grain bed to keep the grain bed a uniform temperature and not scorch the liquor. I have heard of problems in RIMS like designs before but I figured that even if it didn’t work as planned, I could always direct fire the mash for Single Step infusion and use the direct fire to kill the enzymes for mash out.

My solution to collecting as much liquor as possible was to make the bottom of the mash tun at an angle with the drains for the recirculation and boil kettle on the low side. You may wonder why I have two drains instead of one. There is one for the boil kettle and one for recirculation pump so I could keep the pump connected while collecting the wort. This way I can avoid having to move tubing full of hot liquor around (see safety point above) and could reset the bed with the pump or recirculate if I wanted without any fuss.

I wanted to make the mash tun easy to construct for several reasons. Foremost is that I had just finished 6 months of welding and had never built anything this big before, so I figured that less is more. Another reason is if I ever had to build another one, I could do it within minimal time. And lastly, I was trying to complete it in the last week of my welding course and didn’t have a lot of time.

In the end I came up with a rectangular container with a slopped bottom able to hold 20+ gallons of water with a stainless steel false bottom screen. I don’t want to get too much into math but I figured that most containers are round because you use less material per volume of container than in a rectangular shape. At the same time, the cylindrical shape uses a larger footprint or area than a square shape (I can show you the math if you really want to see it). On top of that, it would be hard to cut a precise bottom for the cylindrical shape so a rectangular shape made more sense.

Another way I made it easier to make was to incorporated butt welds and fusion welds throughout instead of more complicated welds which would have numerous complications in preheating the metal. I also made the design so that if I was off in cutting or if it warped a little from the heat, it could still be put together without redoing the whole piece (luckily this didn’t happen).

For measurement of temperature, I was able to find some cheap thermal wells at the junk yard and purchased others from a local supplier. I place the thermal wells into the mash tun, one in the reservoir and one in the mash itself. This way I could monitor both the temperatures and make sure I don’t heat the enzymes too much and know when I’ve hit the right temperature for the mash.

I also placed a lip on the top and bottom so that I could place insulating redwood slats around the vessel to help keep the mash temperature steady and still be able to afford some protection to the wood from water getting behind the slats. The lip also made it possible to have a Lid with a decent seal; which really helps in heating and keeping the mash at a stable temperature.

The mash is heated by a couple of jet burners placed on the stand. I used two so that I could widen the area that I’m heating to reduce the possibility of scorching. If I want to really heat up the strike water for single infusion, I can turn on both burners and do it in a flash. With one burner on and 12 gallons of water in the tank, it takes less than 30 minutes. I haven’t tried both yet.

The whole thing sits at the top of my brewery on a couple of rails of stainless tubing. It can be easily taken down to dump out all the grain. Unlike my previous mash tun, I left the opening clear of obstruction to facilitate the dumping of the grain. I used to have a lip around my converted keg mash tun that would trap grain when you tried to dump it.

There are some changes I would like to make to my mash tun now that I have used it. Some of these include a new sparge apparatus to allow a float valve to automatically keep the level while sparging. I will modify the mash lid to allow for the sparge head to be clamped at the appropriate height and also allow the recirculation manifold to sit in the tun and be removed if necessary. I may also want to add a motorized stirring mechanism at some point in time to further mix up the mash.