Homebrewing: How to Build a Mash Tun


Tips and techniques to help you brew better beer at home.


[Photos: Peter Reed]

Hamlet asked whether to be or not—an important question for someone whose uncle murdered his father then married his mother to become king. Homebrewers also have an existential question: to all-grain or to extract? The consequences are arguably less profound, but the choice impacts the entire approach to brewing.

Brewing with extract has many advantages: startup costs are low, little equipment is needed, brew day is short, and recipe planning is simplified. But these advantages come at a cost—principally, less control over the beer. (As well as less tinkering and fewer gadgets for those of us who enjoy the mechanical aspects of brewing.) Extract brewing is also more expensive than all-grain in the long run.

I will probably make some enemies here, but I believe the added control gained from all-grain brewing makes the brewing process fundamentally different from brewing with extract. Imagine giving a recipe for chocolate cake to two reasonably competent bakers. They will most likely make two very similar cakes. Now imagine giving a recipe for pasta tomato sauce to two reasonably competent cooks. They might make identical sauces, but they probably won't, because so many variables are open to interpretation: how long to sauté the onions, how fine to chop to the garlic, what temperature is "medium-low heat," how much salt and pepper and red pepper flakes is "to taste," the splash of vermouth or half teaspoon of sugar that wasn't on the recipe but seemed like the right thing to do.

Brewing with extract is more like baking a cake. You can excel by choosing a good recipe and fine ingredients (read: fresh extract). All-grain brewing leaves much more opportunity to exert style. Some of the variables include malt crush size, mash temperature, single-step versus multi-step mashing, infusion versus decoction mashing, mash all grains together versus mash some and steep some. The list goes on. Like baking or cooking or extract brewing, you want to start with a good recipe and good ingredients. But you have many more opportunities to shape the final beer.

All of this is by way of introduction to some necessities of all-grain brewing. The first and most important is the mash tun.

How to Build a Mash Tun

The mash tun is where the magic happens. Essentially, it is an insulated vessel with a filtered drain. Milled grain is mixed with heated water in the mash tun and allowed to sit for 60 to 90 minutes, typically, while enzymes in the grain break down complex sugars into simple sugars that yeast can digest. Then, the hot liquor is drained out of the mash tun into the kettle, leaving behind spent grain. In the spirit of all-grain brewing, I'm going to discuss some of the important features of a mash tun, but I will leave the details of construction to you.

The Vessel


My mash tun—a simple Coleman picnic cooler.

Homebrewers have made mash tuns from picnic coolers, water coolers, and old beer kegs. You want a container that is large enough for your brewing system. If you brew five-gallon batches, a 10-gallon mash tun should be large enough. Picnic and water coolers are inexpensive and have built-in insulation, but they cannot be heated externally. If you go this route, you will need to add already-heated water to the tun, which can be heavy and hazardous. If you use a keg, on the other hand, you can heat it from underneath with a propane burner, but you will want to add a layer of (fireproof) insulation around the keg to help maintain steady mashing temperatures.

My System: I use a Coleman 8-gallon picnic cooler for 5.5-gallon batches.

The Filter


My filter, upside down.

The purpose of the filter is to allow the hot liquor to drain from the tun while leaving behind the spent grain. The type of filter you choose depends in part on the shape of your mash tun. Because you want to drain all of the grain equally, you need a filter that spans the bottom of the mash tun. Popular solutions for round mash tuns include a false bottom or braided stainless steel dishwasher hose, stretched out a bit. For rectangular mash tuns, you may need to construct a filter out of pipes. Just be sure your materials are food-safe and can stand up to temperatures up to 180°F.

My System: For my rectangular mash tun, I built a filter out of high-temp-grade plastic pipe with a couple hundred slits sawed into it.

The Drain


My mash tun, draining into a kettle.

The drain is simple enough. You need a ball-valve—either stainless steel, copper, brass, or food-grade plastic. You will also want a hose that can withstand high temperatures to connect to the drain and lead to the kettle.

My System: I have a plastic ball drain and two feet of silicone hose.

Show Us Your Setup!

A quick search online will uncover myriad homemade mash tuns. This site has some good guidance. But we want to see YOUR setup. Email a photo (horizontal is best) to [email protected] with a brief description of your setup by Friday, September 30th and we'll put up a slideshow here on Serious Eats: Drinks.

Welcome to the all-grain dark side! In the coming months, I'll discuss other aspects of all-grain brewing, but don't wait, start brewing!