Screwy's 5 Gallon Mash Tun

Today I assembled and tested my 5 gallon mash tun made from parts I bought off the shelf at my local Home Depot (see complete parts list below). The Rubbermaid cooler cost $20.00 and the other assorted plumbing parts added about another $35.00. For less than $60.00 you too can built your very own mash tun in under 4 fours, including making a trip to Home Depot.

According to BrewWiki this type of cooler is ideal for infusion mashing where hot water is added to the grains, and the cooler is then sealed to maintain a constant temperature during the conversion process. A cooler will typically only lose a degree or two (F) during the hour long mashing process. The simplicity of infusion mashing in a Gott type cooler makes it a favorite with brewers. 

Single infusion mashing is the simplest mashing method for at home brewing, it uses room temperature crushed grains added to a calculated amount of hot water and maintaining a fixed temperature for an hour. Accurately calculating both the volume and temperature of the strike water allows you to hit the target temperature for the combined mash, somewhere between the 147 - 155 F temperature range.

 Screwy's 5 Gallon Mash Tun Cost Under $60.00 To Build

Complete project parts list:
1 - Home Depot Store SKU # 442438 Rubbermaid 5-Gallon Jug with Cup Dispenser

1 - Watts 3/8 OD x 7/8 BC x 20 inch stainless steel braided filler connector

1 - Danco 80746 Moen Repair Kit 5/8 O rings

1 - Mueller 107-702 3/8 Ball Valve - Full Port

1 - Crown Bolt Inc. Create-A-Bolt 5/8 stainless steel

2 - Watts A-785  3/8 MIP x Close Nipple

1 - Watts A-773  3/8 MIP Square Heap Plug

3 - Watts A-298  3/8 Barb x 3/8 FIP Hose Barb Adapter

3 - Stainless steel 1/2 hose clamps

Parts Assembly Overview

I made the bottom mash filter in about an hour and I assembled it outside the cooler before installing it. Once it was assembled and the valve adapter and ball valve were tightened I pushed the braid end of the mash filter over the end of the barb fitting and tightened down the hose clamp.

Screwy's 5 Gallon Mash Tun With 3/8 Ball Valve

The Stainless Steel Mash Filter

I spent about 4 hours over the past few days researching how others have already modified 5 gallon Igloo or Rubbermaid coolers and turned them into inexpensive mash tuns. I opted to incorporate the braided stainless steel filter design rather than the false bottom design. For me putting together the parts list and assembling the braided filter was also the easiest to do and all the parts I needed were available at my nearest Home Depot store.

20 Inch Long Stainless Steel Braided Mash Filter

I started out with a 20 inch stainless steel braided water connector that I bought at Home Depot. I then cut off both crimped connectors using a pair of inlaid aviation snipes, you could also use a side grinder or dremel tool to do this. 

20 Inch Length Of Stainless Steel Braided Hose

Many of the braided water connectors on the shelves looked like they were made from stainless steel when in fact they were not, make sure you use the part in my material list you don't want one made from polymers.

Cut Through The Stainless Steel Braiding To Remove The Ends

My aviation shears, or tin snips, made short work of cutting through the stainless steel braiding but be prepared to deal with some very tiny and sharp ends after the cut. I later gently folded the cut ends inside the braid and squeezed them under to create a neat bend before pushing the barb adapter into the ends.

Pull Out The 3/8 Inch Plastic Tube From Inside The Braiding

After both ends were cut off I used a pair of pliers to help pull the 3/8 plastic tubing out of the stainless steel braiding

12 Gauge Copper Wire Coiled For Support

I stripped the ground wire from a 20 inch length of 12 gauge Romex electrical cable and used it to create a stiffener for the inside of the braided mash filter to add support so it wouldn't collapse under the weight of the water and wet grains.

12 Gauge Ground Wire Wrapped Around 3/8 Diameter

A vise grip locks one end of the wire to the 3/8 diameter coil form so it's easy to wrap the wire around it without too much effort.

Mash Filter End With 3/8 Barb And Plug

Attach the end barb to the filter braid using a small stainless steel hose clamp and then hand tighten the plug into the threaded end of the barb to seal it.

12 Gauge Wire Coil Stretched To Length

Stretching the coil by holding both ends firmly and pulling them apart lengthens the coil and reduces it's diameter so it will slip inside the braided mash filter easily.

Trim Coil Wire On Vavle Adapter End

Trim off any excess coil length with a pair of wire cutters after it's inserted all the way inside the braid.

The Valve Adapter

The valve adapter is made from the rubber gasket that comes installed in the cooler from the factory, it forms a perfect seal around the hole in the cooler wall for a watertight fit, a 3/8 close nipple, a stainless steel flat washer and a barb adapter .

Apply Teflon Tape For A Watertight Fit

 Before we get started I want to point out that I Teflon taped most of the connections, the 3/8 valve adapter in in particular as I don't plan on unscrewing it any time soon for cleaning. The plug on end of the mash filter didn't get any tape but the 3/8 nipple did on both ends before it got screwed into the ball valve through the cooler wall.

Valve Adapter Assembly Parts Display

To make the assembly easier remove the spigot that came with your cooler but leave the gasket inside the hole in the cooler wall, this will help provide a watertight seal.

Rubbermaid Cooler With Spigot Gasket

From the inside of the cooler push the valve adapter assembly (remove the O ring first) through the gasket until it can't go anymore. From the outside of the cooler slip the O ring over the 3/8 nipple end of the valve adapter while holding the adapter from the inside.

Valve Adapter With O Ring

On the inside of the cooler you can see the barb fitting a stainless steel washer and part of the valve gasket. I put a slight bend in the washer by tapping it with a hammer while it was laying on the floor with a 1/8 wooden shim under one end. Doing this will allow the flat washer to conform to the inside radius of the cooler wall a little better.

Gasket, Flat Washer And 3/8 Barb Shown

The Ball Valve

The ball valve screws onto the 3/8 nipple end of the valve adapter using 2 stainless steel flat washers as spacers. The spacers provide a tight seal on the O ring and keep the ball valve far enough away from the cooler wall so that the valve handle won't hit into it.

Ball Valve And Washers Tightened Onto Valve Adapter

After the ball valve has been firmly tightened to the valve adapter the braided mash filter connects to the inside end of the valve adapter using a small stainless steel hose clamp.

Gasket Compressed Using Slight Radius In Washer

I filled the cooler with 3 gallons of hot tap water and let it sit for about 30 minutes or so and there weren't any leaks. The gasket, O ring and washers provided a perfectly watertight seal.

A 30 Minute Water Test To Find Leaks

The mash filter and 3/8 ball valve emptied 3 quarts of 115F water in a minute and easily provides a fast enough flow rate for my Mr. Beer sized batches.

3 Quarts Per Minute Water Flow Rate

The last step in the assembly was to screw on the 3/8 close nipple, barb adapter and push on a length of 3/8 plastic tubing.

The Completed 3/8 Ball Valve And Barb Assembly

I've read online where other brewers said they liked using ball valves because the valve design makes it easier to clear out a clog simply by twisting the handle between open and closed. The consensus I researched among brewers regarding stuck mashes favored using the braided stainless steel mash filter design over the false bottoms as well. The braided stainless steel filter is easy to clean, less prone to clogging, simply to make  and empties more completely than some false bottom designs.

 Mash temperatures play a significant role in the creation of your wort and the beer that is made from it. Many brewing publications agree that the optimum temperature range for an infusion mash ranges from 147°F to 155°F. A mash done at the lower end of this range will produce a well attenuated lower gravity beer and a mash done at the higher end of the range will produce a dextrinous higher gravity beer.

Now that my new mash tun is ready to go I will be using my Mash Temperature Calculators to help me figure out my mash thickness, rest boil times, strike water volume and temperatures for both mashing and sparging.

11 Pounds Of Mixed Cracked Grains

 I regularly add 11 pounds of grain to my mash tun now and at a 1.25 mash thickness it takes up a total volume of 4.5 gallons leaving me enough extra room for adjusting to my target temperature if needed. I do 60 to 90 minute single infusion mashes for my recipes and lauter for 30 minutes using a fly sparge process.

Fly Sparging With 168F Strike Water During Lauter

The 5 gallon size is perfect for brewing either a single 5 gallons batch or two Mr. Beer sized batches like I do. The tun is small enough to fit inside my sink and that makes it really easy to clean. I've never mashed using a 10 gallon tun but I think it might be easier using two 5 gallon tuns instead.

Lifting And Cleaning The 5 Gallon Tun Is Easy

I've brewed around 10 all grain recipes so far using my mash tun making it the centerpiece of my brewhaus because without it I'd be lost. Initially I had to do quite a bit of calculations to determine the mash thickness, total volume and how to hit the target mash temperatures. I wrote them all down and for the first several brews made some modifications mostly to temperatures.

Lautering Into Two 12 Quart Pots For Mr. Beer Sized Batches

Now I know from memory that adding 11 pounds of grains and filling the tun to the 4.5 gallon mark will give me a 1.25 mash thickness. I also learned that by preheating the tun with 160F water for 20 minutes and using my Mash Temperature Calculators I can come pretty close to hitting my target mash temperatures, making my brew days a lot more fun.

My mash tun has been heavily used for a little over two years now since posting this original design, so I decided to update this post to go over what I've found to be the best way of maintaining it. All I've ever done to maintain the mash tun is to remove the spent grains and thoroughly rinse out the insides with clean water until there were no grains left inside. Then I just turned the tun upside down with the top facing down on a towel and a small air space under one side so all the water could drain out. Once most of the water had drained out I turned them right side up so they would air dry.

Filter Braid Inspection After Two Years Of Heavy Use

I've recently torn down my mash tun for inspection and after dissembling the filter braid I found no signs of verdigris on any of the parts that have come in contact with the wort. All the copper and brass parts had developed an even dull colored protective oxide layer on them that protects the wort from contamination.
I've read posts in some forums where white vinegar and salt, or StarSan was used to clean the copper parts and get them shining like new. After reading John Palmer's article I decided I'll just use clean water to remove and bits of grain and keep the protective oxide layers that have already built up on mine.

The 10 Gallon Version thanks to Craig Horton who was thoughtful enough to share his parts list with us list for those who may be interested in build your own 10 gallon version of his design. Craig has also provided me with a picture of his build.

Craig Horton's 10 Gallon Design

Thanks for posting the parts list, the pictures and the step-by-step instructions. I did a slight modification by using a T-Connector (Watts #A-168 Tee Connector 3/8 in FL) and a Coupling (Watts #LFA-760 Coupling 3/8 in FIP). Concisely, I followed your exact instructions and connected the braided mash filter to the other end of the T-Connector instead of using the Plug (Watts A-773 - 3/8 MIP Square Heap Plug). The Coupling fits between the T-Connector and the Nipple with the braided mesh essentially forming a circle in the bottom of the mash tun. I just completed a water test and this looks good to go. I plan to brew an APA on the 6th and I am looking forward to my first all grain brew. Thanks again for posting the information. ~Craig