Build a Cooler Mash/Lauter Tun

You finally got that 10-gallon round beverage cooler to make a mash/lauter tun, but now what? What type of false bottom works best? How do you hook everything up? What about sparging? After countless hours at the hardware and homebrew stores I have come up with this simple yet practical and cost-effective design.

The first and most important thing you must consider is the false bottom. Some false bottoms don’t fit very tightly and let grain get by. Others may float when you dump in the grist if you mash in a separate vessel. My false bottom is made from stainless-steel mesh and food-grade plastic. It is sturdy, won’t float or move when you stir, and has handles to make it easy to remove for quick cleaning. There are also no tubes or manifolds to get hooked on when you stir.


• Stainless steel or brass mesh, 1.5-ft. square
• 3.5 feet of  1/4 in. thick by 2 in. wide UHMW food-grade plastic
• 3.5 feet of  1/4 in. thick by 1 in. wide UHMW food-grade plastic
• 16 8-by-32 in. stainless steel machine screws, 1/2 inch long, with nuts

A variety of stainless steel and brass mesh can be purchased from McMaster-Carr (708-833-0300). Catalog No. 9230T72 is a good choice and sells for $3.63 per square foot. For the food-grade plastic, check the yellow pages for a plastics dealer in your area. You should be able to get the amount recommended for about $5. Any well-stocked hardware store will have the screws and nuts for a few cents apiece.

Step by Step

If you are using a 10-gallon Gott cooler, cut the two-inch-wide piece of plastic to a length of 39.25 inches. If you’re using something else, you need to figure the right size. Remove the spigot from the cooler; make a loop with the plastic, letting the ends overlap; and push the loop all the way to the bottom of the cooler. With the plastic fitting snug against the inside wall of the cooler, mark the spot where the ends overlap and cut there.

The one-inch-wide piece can be cut to 37.5 inches long or marked in the same way as before by fitting it inside the two-inch piece while it is inside the cooler. Cut a notch in the center of the two-inch piece 1 1/2 inches high by 1 7/8 inches at the bottom and 1 1/4 inches at the top. This will allow it to fit over the spigot (See photo, page 37).

Draw a line one-fourth of the distance from either end of the two-inch piece. Using a 3/8-inch drill, make two holes 3 1/2 inches apart on either side of the line and about one-quarter inch from the top. (The open part of the notch you cut is the bottom.) Remove the material between these holes using a jig saw; these will be the handles (see photo, page 36). Set the two-inch piece aside for now.

In the one-inch piece of plastic, drill a 9/64-inch hole one inch from either end. Bend the plastic to form a hoop. Drill two 9/64-inch holes two inches apart in a short piece of leftover plastic and temporarily fasten it to the inside of the hoop with two of the screws and nuts. This forms the inner frame of the false bottom and will be used to shape the mesh.

Place the frame on a flat surface, center the mesh over the frame, and press the center of the mesh down to the surface. Pressing down the center of the mesh allows the false bottom to rest on the inside bottom of the cooler when completed. This reduces the amount of foundation water needed and reduces the possibility of poking a hole in the mesh when stirring the grist.

Now start bending the mesh over the top and outside of the frame. You will probably need to trim the mesh before bending it down the outside. To do this, mark all the way around with a permanent marker so that none of the mesh inside the marked area will extend below the frame when folded over and along the outside. Remove the excess with tin snips. Finish forming the mesh and set aside until needed again.

Next, you need to put the two pieces of plastic together. Remove the scrap piece of plastic from the one-inch piece. Start at the notched area of the two-inch piece. Position an end of the one-inch piece so the top is flush with the top of the two-inch piece and centered on the notch. Drill a 9/64-inch hole through the existing hole in the one-inch piece through the two-inch piece.

Countersink the hole on the outside of the two-inch piece so when a screw is placed through it the head does not extend beyond the surface. Use a screw and nut to hold these two pieces together. Bend the one-inch piece around so it meets itself and drill another hole like the first one, countersink it, and fasten with a screw and nut.

Now bend the two-inch piece around the one-inch piece so the bottoms are flush on the opposite side from the notch. You can temporarily hold it in place with one or two C clamps. Notice that the one-inch piece slants from front to back. This is normal.

Continue drilling evenly spaced holes, about 2 1/2 to 2 3/4 inches apart, from the notch toward the ends of the two-inch piece, and countersink them. There should be 16 holes in all including the two originals, eight on each side of the notch going toward the opposite side (See photo above).

After all the holes are drilled, take the assembly apart and reassemble everything with the mesh. Start at the notch again and use an ice pick to line up the two starting holes and pierce the mesh. Continue around in this fashion with the ice pick and screws. When all the screws and nuts are installed, tighten everything up. Don’t worry if it is not perfectly round; that’s another reason for leaving slack in the mesh. It will form to the inside of the cooler if it was cut correctly.

On with the Flow

The spigot that comes with the cooler is useless for lautering. I have replaced mine with an inexpensive good-grade plastic bottling bucket spigot that I got from my local homebrew supplier. He gets them from G. W. Kent, catalog number 2806. You can get this or a similar product from your homebrew retailer. (G.W. Kent doesn’t sell retail.) The old spigot can be removed quite easily by loosening the plastic nut on the inside. Just make the hole a little larger; the new spigot will fit right in place.

Be careful when enlarging the hole. Use a sharp, thin knife and remove just enough plastic from the top side of the hole so the new spigot fits. The hole should be about one inch in diameter. There is just enough room from the bottom for the plastic nut to fit on the inside of the cooler, so don’t remove any plastic from the bottom part of the hole.

Place the false bottom in the cooler to see how it fits. The inner part of the frame will probably have to be trimmed in the area of the notch so it fits around the spigot (See photo below).

Rinse Cycle

Making a sparging sprinkler from a short piece of copper tubing is very easy. I used a 23-inch-long piece of three-eighths-inch OD copper tubing left over from my wort chiller. Crimp one end shut with pliers. Starting at the crimped end, bend it in a circular shape. I bent mine around a 4.25-inch-diameter paint can. Finish with an offset bend so the tubing is level when resting on the edge of the cooler (see photo, page 34). You can cut a notch in the lid of the cooler or melt a notch with a soldering iron so the sparge sprinkler just fits (see photo, page 34). This will keep it in place when sparging. Now drill a series of 5/64-inch holes in the tubing, about three-quarters of an inch apart, angled out from the bottom of the loop.

The last thing is making your new system work. Put the false bottom in the cooler. Add one or two quarts of foundation water at the desired temperature. Combine the crushed grain and water to reach your desired strike temperature, and mash for the correct amount of time.

Set the cooler on a chair. Place the sparge water container on a shelf or countertop that is higher than the cooler. Connect the sparge sprinkler to the sparge water container with a length of 3/8-inch ID (inner diameter) vinyl tubing. Place the sparge sprinkler above the mash and replace the lid on the cooler to hold it in place.

Adjust the vinyl tubing so that the sparge sprinkler is level. Connect another piece of vinyl tubing to the spigot on the round cooler and run it into a food-grade bucket or brew pot. Turn on the spigot to start the runoff from the mash. Then turn on the sparge water. Now all you have to do is monitor the flow rates to make sure nothing overflows.