How to make a Coffin Mash Tun

A local homebrewer has long had a large cooler he mashes in that has been dubbed the coffin. For NHD 2006 we decided to make a coffin for club use (CARBOY) and to do a 20+ gallon batch of 1.090 beer. The large cooler was a donation to the club by a member so all that was needed was the parts to assemble the system and the time to drill the tubing. The cooler that was donated was about 140 qt.

Having made a 100qt cooler conversion for another brewer out of CPVC, I knew that it could easily be accomplished out of a few parts from the local home improvement store and local homebrewing shop. It uses a bottling spigot much like my other two rectangular mash tuns but then instead of a coil and copper, it is laterals of CPVC. If we were batch sparging we could have used a single outlet point and a braid or a SS scrubbie on the back of the bottling spigot, but due to the need to maximize grain in the batch, not enough room remained for the sparge water additions, so we elected to make a fly sparge system. The key is to keep the laterals off the walls to avoid channeling through the grain.

Here is the parts list and the prices paid (including tax):

Price each
Bottling Spigot
Extra Gaskets for Spigot
90º Elbows - 1/2" CPVC
45º Elbows - 1/2" CPVC
Tees - 1/2" CPVC
3/4" x 1/2" Reducer Busing CPVC
3/4" Threaded Female to Glue Female CPVC
    Grand Total

Parts for the manifold (note that three Tees are not pictured)

The layout is pretty simple. The bottling spigot will be put into the cooler through an enlarged drain hole after the old drain is removed. The 3/4" Threaded Female connector will then be used on the backside of the bottling spigot and additional gaskets as needed. The bushing will reduce the size from 3/4" to the 1/2" CPVC.

From there the 45º Elbows can be used to get the pipe system to lay flat on the bottom of the cooler. The 90º Elbows are for the corners and the Tees are for the middle laterals and connecting to the 45º Elbow section. Of course your cooler configuration may differ, some coolers have the drain lower and some higher, your parts list would need to be adjusted for your configuration and cooler.

In looking at the bottom inside of the tun (be sure to measure the bottom, not the top, most coolers taper), it became apparent that there was only enough room for 3 laterals if space was to be left at the sides to avoid channeling. I like to drill everything in the field, lats and connecting pieces, but I don't drill any fittings.

Let's run through the tun fabrication from start to finish.

First up, remove the existing cooler drain.

The cooler drain is generally threaded with a coupler tightened on the inside and a few gaskets. Once this is removed the hole may need to be enlarged. If so mark the cooler using a gasket from the bottling spigot as the guide and then remove the marked area.

For enlarging the drain hole I use a spiral saw, and mine just happens to be coordless. I have used other methods in the past from utility knives to saws and most are too violent for the operation and can end up damaging the cooler.

Once the hole is enlarged, insert the Bottling spigot with a gasket on the outside and at least one on the inside. Then tighten down the 3/4" Threaded female. On this cooler it took two inside gaskets to make that connection.

After the spigot is installed the next piece is the bushing and then later you must figure a method to either move upward to the manifold or downward. If upward you may be able to use a single 45º Elbow, on ours to move downward it took two 45º Elbows and some transition pipe. This is probably the most difficult part to create so save it for last. Move on to the manifold. Try to stay 2" off the walls at all times. That should allow you to cut the laterals, three in this cooler. Measure the inside length and cut the lats 5-6" shorter. 2" for each end and ~1" for the elbow. You can always recut them even shorter, but to add back will take a coupler. The nice thing is that the pipe is extremely inexpensive if more is required.

Once those are cut, trial fit them with the elbows in the bottom to see how you did. In my case the middle lateral had to be moved down in order to accomodate the transition piece for the manifold to lay flat. If this is the same in your case, just cut a short 1-2" piece of pipe for the bushing, put on the 45º Elbow and then take the other elbow and a short straight edge and find the point where you can get them lined up and one is on the bottom of the cooler at a 90º angle to any lateral. In this cooler it took a cross piece and a few extra Tees to make the connection work out.

Once the lats and the connection to the back of the valve is decided, drill the bottom side of every pipe piece that lays flat to the bottom and that is 2" away from the walls with a 5/64" bit. I used a two speed cordless drill and found that the low speed setting was best. Put the holes fairly close together, no more than 1/2" apart.

After drilling, reinstall the mainfold and see if any joints need gluing. Most of the time, none will. In this cooler only one required glue. Use cleaner and glue designed for CPVC.

Now you'll have a coffin mash tun all ready for those team brews!


This tun was used for our2006 NHD brew and achieved 78% efficiency on a 70 lb grist and a 23 gallon finished batch size.


NOTE: Use CPVC for the mash tun manifold, not PVC. CPVC is made for the temperature ranges of mashing, PVC is not.