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My best 51st birthday present was a vivid orange Rubbermaid cooler, a cylindrical beverage dispenser complete with Dixie cup holder. It begged to become my first mash tun.   

I’d read, surfed, chatted with every homebrewer I know, and examined others’ efforts. It was clear that an insulated mash tun was the way to go, whether it took the form of a half-barrel covered in space-age Mylar and aluminum-faced bubble wrap or a lowly cooler. My 40-liter brewpot decided the issue; the Rubbermaid was it.    

No matter what kind of vessel you choose, it’s how you get the wort out that’s the problem. You need a bulkhead fitting to penetrate the side of the container. Figuring out the right parts takes some power shopping; what you want and need is not always on the shelf.   

The next question is how to filter your grist. Would you use a manifold or a false bottom? A slit-pipe manifold is easy to construct out of CPVC or copper pipe, requiring only an hour’s work with a hack saw or scroll saw. But a false bottom appealed to me even more because it would allow total flow from the grain bed. More flow, less chance of a stuck mash. More important, a false bottom would allow me to construct a recirculating infusion mash system (RIMS) down the road in the easiest way I’ve ever seen.   

A lot of my knowledge came from CompuServe’s wine and beer forum. I had other sources, too. Last year I visited another local homebrewer, Jack Adkins. His RIMS was the height of simplicity. Suspended in a cylindrical cooler was a stainless steel colander. Below that was a heater coil set opposite the RIMS pump suction inlet. I loved the idea of simply heating the underlet water/wort and recirculating it. No other external gadgets. I wasn’t ready to make that big jump to a RIM system, but I decided to build my mash tun RIMS-ready so I would be prepared in the future.    

But where to get this magical colander? Or how to make some other false bottom?   

At a meeting of my homebrew club, the Mid-Michigan Maltmeisters, Bob Beagen was telling everyone how he’d constructed a false bottom from pizza screens (Beagen manages a restaurant specializing in pizza). But what the heck is a pizza screen?   

Well, it’s round, made of expanded metal, and costs less than two bucks. A pair of screens coupled with some copper, bronze, or stainless steel mesh sounded like a perfect false bottom. Two pizza screens would provide plenty of rigidity. If they would fit the cooler.   

It turns out that pizza screens come in a 10-inch size, the same as the diameter of the Rubbermaid cooler. A marriage made in heaven. (Or hell, as I’d later discover that pizza screens are less than perfectly round.) I found them in a restaurant supply store.   

A visit to the local mega-hardware outlets provided the plumbing parts. I already had the Rubbermaid cooler. This project had reached critical mass.

Parts:

• 11/2-in. rubber washers, (use two or four), 67 cents apiece    
• Brass nipple, 1/2-in. x close, $1.11; or 1/2-in. x 11/2-in., $1.48
• 1/2-in. full flow ball valve, $4.99    
• 1/2-in. coupling, $1.75    
• 3/4-in. x 1/2-in. hose barb to MIP (right angle, barb is 3/4-in.) $1.74
• 1/2-in. barb (exit from ball valve), $1.99    
• 3/4-in. hole saw, $2.47 (plus center guide if you don’t have one. Needed only if you don’t have a hole in your cooler.)
• 2 pizza screens, 10-in., $1.85 each
• Copper or bronze screen, $2.50
• Miscellaneous parts: pop rivets, aquarium or food-grade silicone seal, and Rubbermaid cooler.

Putting It Together:   

First I laid out all the bulkhead parts. Would they work? A dry fit showed several things. First, I didn’t need the hole saw; the Rubbermaid spigot opening is larger than a 1/2-inch pipe, so the problem would be sealing the plumbing, not drilling a larger hole.   

The dry fit showed that the flat rubber washers I’d purchased would not work, at least on the outside. A rubber “O” ring would be needed. Fortunately I had some on hand. I screwed the pipe nipple into the ball valve, sealing it with food-grade PTE pipe dope on the threads (personal choice, some prefer Teflon tape for pipe sealing).   

I tried fitting the pipe nipple with only the connection on the inside. It was apparent that the back-and-forth action of the valve handle would cause stress fractures — leaks — in a short time.

So I tried to find a suitable large-shouldered washer, one made of brass or stainless steel. Nothing in my shop fit the bill, and the sheet of brass plate that “had to be there somewhere” eluded me. But I found a sheet of acrylic plastic. I would have preferred Lexan, a type of plastic that is virtually shatterproof, but none was available. So I used a rectangle of acrylic for my internal washer.    

After drilling a pilot hole in the acrylic, I used a scroll saw to enlarge the hole to 3/4 inch. That wasn’t quite large enough, so I used a Dremmel tool to drum sand a larger hole. A file would do an equally good job.   

That left sealing the hole. In front, backing the ball valve, I used that rubber “O” ring; it happened to fit perfectly in a depression molded into the plastic of the cooler/mash tun. It also fit the nipple tightly. On the inside I cut a larger hole in one thin rubber washer, fit it on the pipe, slipped on the acrylic washer, and finally screwed on the brass connection. That completed the bulkhead-valve assembly and gave it plenty of support. Next, the false bottom.   

Making the false bottom was straightforward. One pizza screen, two layers of copper/bronze screen cut to fit, the second pizza screen on top.  I thought of using a food-grade silicone seal to bond the parts, but chose to pop rivet the sandwich together instead. Only afterward
did I try to fit the completed false bottom into the cooler. Oops.    

The screens weren’t perfectly round. I solved that with a large pipe clamp, squeezing the sandwich gently into roundness. It is still an extremely tight fit — so tight that it doesn’t fit easily even when the Rubbermaid mash tun is filled with 156° F water.   

Next came finding a method of holding the false bottom off the bottom of the mash tun. Even with the incredibly tight fit it might tilt or pivot and spill the mash.   A handful of CPVC angles, T’s, and pipe made into a square sized to fit under the false bottom provided underlet. And the volume of makeup water could be adjusted by making spacer legs, short or tall. I started at 1.5 inches tall, just enough to hold everything above the bulkhead valve, then measured more accurately and discarded the standoffs. (Later this year, after I plumb in a heater and recirculating pump for the RIM system, I’ll raise the false bottom higher to clear the heater element.)  

That’s it. Two pizza screens, some metal mesh, CPVC plastic, and a few plumbing parts. Less than $50 (less than $20, since the cooler was a gift). Why had I waited so long to switch to all-grain?

Revving It Up:   

The final questions could be solved only by a trial mash. Would I need a handle on the screen for removal? Yes. A stainless steel or copper “chore boy” (scouring sponge) to aid in filtration? No. Another homebrewer suggests adding a small vertical pipe to admit extra water to refloat the grain bed if the mash sticks. What about using a sparge arm or other sprinkling system — vs. batch sparging? Too much thought, not enough action.   

My pal Kim Kowalski, head brewer at the Blue Coyote Brewing Co. in Lansing, Mich., and I decided “no guts, no glory.” Our first test was a pair of wheat beers, each with 50 percent wheat and, using a protein rest at 122° F, a two-step mash. Guts, real guts.   

A homebrewing spreadsheet from the Web required calculating the thermal mash of the mash tun. Just add hot water and measure temperature drop. After that calculation, the software produced a first mash-in temperature. Doggone — we came within a degree of 122° F the first time. The second infusion of boiling water to reach a 150° F conversion temperature went perfectly — after we stirred vigorously to eliminate hot and cold spots.    

What we didn’t expect was the temperature of the first run-off; the underlet was at least 5° F cooler then the grist itself. Still, that first six-gallon batch was 1.051 vs. the predicted 1.050 with 80 percent utilization. Hmmm, 80-plus percent on my first mash? Not bad at all!   

When it was Kowalski’s turn to mash, we used the same first-infusion temperature. Then, when adding the step-up water, we recirculated several pints of wort. That appeared to stabilize the temperature more uniformly. And at mash-out we took the first runnings, about eight 16-ounce pitchers, and heated them to 165° F in a microwave.    

Kowalski’s run-off stabilized at 162° F during our batch sparge. Both sparges were “slow” but steady at about one quart per minute.
Kowalski and I don’t really know yet how to manage this mash tun perfectly. That will take a lot more brewing. Does it require a bit higher temperature than calculations predict? Should we heat the makeup water a few degrees hotter? Should I reheat the first runnings before returning them, to aid the sparge? Some of those questions will be moot when I add a RIMS pump and heater. The answers to others simply await the next 10 or 20 brews.

Thom Cannell is a homebrewer in Lansing, Mich., and president of the Mid-Michigan Maltmeisters homebrew club.