Converted Mash Tun Cooler & Hot Liquor Tanks

Building And Using Coolers As Mash Tuns

I am making the assumption that a brewer who reads this article will probably not be a beginner. Most of you have probably brewed several times already and are looking to educate yourselves about new techniques.

It is with this assumption in mind that I present this article on how to construct (and use) a mash/lauter tun adapted from an ordinary insulated picnic cooler. This article is not intended to be a complete tutorial on all-grain brewing. Instead, it provides tools you can use to move into all-grain brewing with equipment adapted at home. It presents basic information on the construction of a picnic cooler mash tun and, at the same time, some usage tips from my own experience. My goal is to illustrate why this method of mashing is truly the easiest way to step into all-grain brewing.

Kick the “Bucket-in-a-Bucket” Method Good-Bye

All-grain brewing differs from extract brewing in that you use various vessels to mash the grain, collect the sweet wort, and boil the full volume of wort. Ten years ago, the most popular all-grain method was probably mashing in a large pot on the stove and then transferring the mash to another vessel for lautering (the process of separating the dissolved sugars from the grain, which produces the wort).

The original (at least the most popularized) home lautering sysrem was probably the bucket-in-a-bucket false bottom championed by Charlie Papazian in the Complete Joy of Homebrewing. This setup is fairly effective and very cheap to assemble. Using two food-grade 5-gallon buckets, the inner bucket is drilled with lots of small holes to form a false bottom that holds the grain and allows the liquid to run off; the sweet wort passes into the outer bucket and is drawn off through a hole in the side. Though simple, this method is vessel-intensive — you mash in one vessel, lauter through two more, and yet another vessel is needed to heat water for rinsing the grain (sparging). This setup has served home brewers well over the years and continues to do the job for many.

Picnic coolers, on the other hand, offer significant advantages not available with buckets, adding both simplicity and efficiency. A cooler’s built-in insulation provides better mash temperature stability than a bucket can provide. Their size also allows mashing and lautering in the same vessel. Thus it’s as simple as pouring the grain into the cooler, adding hot water, waiting a bit, and then draining the sweet wort.

Coolers offer more options for lautering, accommodating both traditional false bottoms and the simple slotted-pipe “manifold” system described in this article. Ready-made false bottoms are available for some coolers, but the system I advocate building is cheaper and easier to build. Manifolds also are less likely to allow the mash to become compacted during lautering, resulting in a “stuck mash” (or “stuck sparge”), where water will not flow through the grain bed. They can be built to fit whatever type and size of cooler you have. The total investment for the cooler and all the parts required to convert it into a mash tun and manifold is usually less than $50. Everything you need to build one of these tuns is readily available at a hardware store.

Choosing Your Cooler

The basic requirements of a combined mash/lauter tun are few. The tun should be able to hold the heat of the mash well enough that the rest temperatures can be maintained for an effective length of time, it should be large enough to comfortably hold the amount of grain and water necessary for the mash, and it should have an effective method for separating the wort from the grain (we’ll discuss grain separation later).

A picnic cooler with a manifold system easily meets these requirements. You can use either a rectangular ice chest cooler or a cylindrical beverage cooler. Beverage coolers are usually more expensive than ice chests; they can cost about $40, compared with $20 or less for the rectangular. The cooler can be 5–10 gallons in size, depending on how much beer you intend to make in one batch.

Look for a cooler that’s sturdy and that doesn’t smell excessively of plastic. If it does smell, washing it with bleach water or leaving it in the sun for a while will usually take care of most of the odor. A tight-fitting lid will help to maintain the mash temperature. An existing drain will eliminate the need to drill a hole.

Heat retention: The heat-retaining requirement is not hard to meet in an insulated cooler. For example, a beer with an original gravity of 1.054 S.G. (13.27 °P) using 9 lb of grain and 3 gallons of water for the mash will have a fair thermal mass, but a decent cooler will keep the temperature of the mash steady (±2 °F [1 °C]) for more than an hour.

Sizing: To decide how large a cooler you will need, the first thing to consider is how much grain you will be mashing. The grain bill will be determined by the original gravity of the beers you intend to brew. Next, figure out the volume of water you will need to mash in. A good place to start is to use 1 qt of water per pound of grain. At this ratio, the grain is fully saturated and fills a volume of 42 U.S. fluid ounces. More water per pound only adds its own volume. Thus, for those home brewers who prefer a ratio of 1.5 qt per pound of grain, the mash volume of 1 lb of grain would be 42 + 16 = 58 fl oz.* Table I, “Mash Arithmetic,” gives some guidelines for calculating mash volumes.

*The thickness of a mash can affect the efficiency of the enzymes at work on the malt’s starches. In general, a thick mash offers more protection for the enzymes and can result in more yield, though lautering may take longer than for a relatively thin mash.

As the table suggests, a 5-gallon cooler works well for 5-gallon batches of normal-gravity beers (up to 1.060 O.G.). Coolers of this size can easily hold 10 lb of grain and the water to mash it. A larger cooler, however, will give you more flexibility in the amount and strength of beer you can make. Ice chest coolers are usually sized at 34 or 48 qt (8.5 or 12 gallons) and are a good choice for high-gravity 5-gallon batches or normal-gravity 10-gallon batches.

Before buying an oversized cooler, bear in mind that the cooler’s volume, in conjunction with its shape, determines the all-important grain bed depth. It is important to have a minimum grain bed depth of at least 4 inches. If the grain bed is too shallow, it won’t form an adequate filter bed and will not clear the wort sufficiently; too deep, and it will tend to compact and lead to the dreaded stuck mash. The optimum depth for home brewers is probably about 1 ft. For this reason, it’s important that your cooler be appropriately sized. When brewing 5-gallon batches, I prefer to use the 5-gallon cylindrical or the 34–36 qt rectangular coolers. These smaller sizes give a good grain bed depth for 1.040–1.060 S.G. (10–14.7 °P) beers.

Putting Your New Tun Through Its Paces

Single-rest mashing: One drawback to picnic coolers is that, while they are great for holding a given temperature, they cannot be directly heated, which makes a step mash with multiple temperature rests trickier. The basic single-infusion merhod, however, does the job for most beer styles. If you’re interested in trying a step mash with your cooler, the box, “Step Mashing in a Picnic Cooler” describes how to calculate what volume and temperature of water to add to your mash to result in the desired temperatures.

In a single-infusion mash, the crushed malt is infused with hot water at a ratio of 1–1.5 qt/lb of grain until it reaches a mash temperature of 150–158 °F (66–70 °C), depending on the degree of fermentability desired. The appropriate strike water temperature (that is, the temperature of the water to be added to the mash) will vary with the ratio of grain and water being used for the mash, but generally a temperature 10–15 °F (6–8 °C) above the target mash temperature will produce the desired temperature when mixed with the dry grain. Note that it is better to add the hot water to the grain rather than the reverse, gradually raising the majority of the grain to the mash temperature as more water is added, rather than subjecting some of the grain (and the all-important enzymes) to a lot of hot water all at once.

The grain should be stirred continually during the infusion to ensure that the mash is completely wetted and evenly heated. Once the mash has reached the desired temperature, the lid can be closed to help maintain the mash temperature for 1 hour. If the initial infusion of water does not achieve the desired temperature, add more hot water according to the calculations given in the “Step Mashing in a Picnic Cooler."

The lauter: Once your mash is finished and all of the soluble starches in the malt have been converted to soluble sugars, you will need to draw off the wort from the grain. This process has been covered in this magazine many times, and I will just provide an overview here.

Extra water is used to rinse, or sparge, the grain to remove as many residual sugars as possible. You’ll need to heat a volume of water for this purpose — typically about 1½ times as much as was used in the mash. The temperature should be no higher than 170 °F (77 °C); at higher temperatures, husk tannins may dissolve into the wort, leading to astringency in the beer (tannin solubility depends on wort pH, so the exact temperature at which this occurs may vary).

Depending on the size of your cooler, you can use one of two methods for sparging: continuous or batch. Both methods begin with a recirculation process, where you draw off a portion of the wort and return it to the cooler until it runs clear of grain particles (one or two quarts should be enough to clear out the cloudiest wort on the bottom). When the wort seems fairly clear of debris, drain most of it into your kettle, leaving about 1 inch of wort above the surface of the grain bed. It is important to maintain at least this level of water throughout the lautering process; keeping the grain supersaturated avoids runoff problems due to compaction.

Batch sparging: Now it’s time to deliver the sparge water to the grain. Although suited to larger coolers, the batch method is simplest: You simply add the full volume of the sparge water to the mash tun, allow the grain bed to settle, recirculate again if necessary, and then drain out the wort slowly. This method is very practical and requires a minimum of attention from the brewer.

Continuous sparging: Continuous sparging involves a relatively slow delivery of sparge water to the grain bed and a slow, concurrent outflow into the kettle. This method demands more attention by the brewer, but may produce a higher yield than the batch method (which could be likened to rinsing off your dishes with dirty water).

Different techniques can be used to add the sparge water, including “sparge sprinklers” that can can be made or purchased, but I believe a submerged tube that delivers the water below the surface works fine as long as the water level above the grain is being maintained. The point is to avoid disturbing the filter bed excessively. If the grain bed is shallow and the flow of sparge water is disturbing it greatly, the flow can be directed onto a plastic coffee can lid to absorb the force of the flow and diffuse the sparge water. The goal is to gradually replace the wort with the water until the run-off gravity is roughly 1.008 (2.06 °P).

Avoiding stuck mashes: It’s very important that the grain bed retain the proper degree of fluidity throughout the sparge. Too compact, and a stuck mash can result. (On the other hand, if the grain is too loose, it will not act as a good filter.) The right flow rate keeps the grain bed from being compacted by gravity.

The flow rate is critical in achieving maximum extract efficiency. In general, the wort should be drained slowly. Total lautering time will depend on the amount of grain in the mash and on the lautering system; most lauters will take anywhere from ½ to 2½ hours. The rate at which sparge water is added should roughly match the outflow rate to keep an appropriate pressure on the grain bed.

The optimum outflow rate depends on the area of your lauter tun and on the efficiency of the lautering system. You can usually get away with playing it by ear, but for those interested in more precise guidelines, a good reference number comes from The Technology of Beer Brewing. The author quotes an initial lautering rate of 0.18 gal/min/ft². To use this number in your system, you need to multiply this value by the area of your lauter tun. For example, a 28-quart rectangular cooler whose internal dimensions are 10 in. wide × 14 in. long × 12 in. high has a floor area of 140 in.² or 0.97 ft². Applying the constant, we multiply the 0.97 by 0.18, which gives a lautering rate of 0.175 gallons/minute. To drain 6.5 gallons of wort at this rate would take 37 minutes. To improve your extraction, use this lautering time as a minimum goal as you monitor your flow.

Optimizing Lauter Efficiency

Lautering is a critical step in the mashing process. All of your work in converting the malt starches to sugars can be undermined by inefficient separation and collection of these sugars from the mash.

Ready-made lautering systems such as Phil’s Phalse Bottom (Listermann Manufacturing Co., Norwood, Ohio) and the EasyMasher (Jack Schmidling Productions, Marengo, Illinois) can be purchased in many homebrew supply shops for use in coolers. You could also make your own false bottom, but it can be quite costly. I urge everyone reading this column to consider the economy and excitement of building your own manifold system.

A manifold can be made of either rigid or soft copper tubing or plastic piping and can be drilled with small holes or slotted with a hacksaw. The wort drains from the mash tun through the manifold, exiting through a drainage setup. The box, “The Basics of Building a Picnic-Cooler Mash/Lauter Tun” describes the manifold construction process in detail, but let’s talk first about some of the principles of manifold design.

General size and shape: The key issue to keep in mind when designing a manifold is the need to span as much surface area as possible under the grain bed while minimizing the total distance the wort has to travel to reach the drain. It is important, therefore, to choose the shape and size that best suits your cooler. In a circular cooler, for example, the ideal manifold shape is a circle divided into quadrants — although a square shape might work just as well. The ideal manifold shape for a rectangular cooler is, of course, rectangular, with enough crossing legs to adequately cover the floor area (see the box, “Manifold Designs.”)

Efficiency: Some of the factors that influence manifold lautering efficiency are flow rate, pipe spacing, and pipe diameter. Lautering should never be rushed; too high a flow velocity through the grain bed to the manifold slots will result in poor efficiency or even a stuck sparge due to compaction by suction (as may be the case with false bottoms). Good manifold design, however, can enable quicker lautering without compromising efficiency.

Manifold slots should be cut halfway through the pipe and spaced about ½ in. apart. As long as the effective total area of the slots is greater than the cross-sectional area of the tubing, then all the slots will contribute equally to the flow and the extraction will be uniform along the length of the tube.

This criterion is easy to meet in most designs. The more difficult requirement is to make the resistance of the valve at the outflow equal or exceed the resistance to the flow at the slots or holes of the intakes. These conditions will ensure that the outflow rate does not exceed the inflow rate. It’s up to you to monitor and control the outflow to keep pace with the inflow. As long as these conditions are met, the outflow will draw equally from all points of the manifold, and you will obtain the best possible extraction from the whole grain bed.

Pipe spacing: The more collection area available, the slower the sparge water can move through the grain bed without altering the total outflow. Because the water moves through the grain bed more slowly, it has more time to extract sugar from the grain. Again, when efficiency is increased, the outflow rate can also be increased, reducing the total time required to lauter the grain bed.

Any slotted manifold will create zones of variable extraction, with better extraction over the slots and poorer extraction between the branches of the manifold arms. Large-diameter tubing has smaller zones of poor extraction between the manifold branches than smaller tubes at the same spacing. Borrowing from another discipline, soil hydrology, calculations show that for lautering on a home brewing scale ¾-in. (i.d.) tubing is the largest practical size and will perform better than ⅜-in. tubing at the same spacing; ½-in. tubing is fairly close in efficiency to ¾-in. tubing and is perhaps a bit more commonly available.

Avoid channeling: If you are to extract as much of the sugars from grain as possible, it is crucial that your design discourage channeling. Liquids tend to flow down the path of least resistance and will form rivers through the grain bed if the manifold is poorly designed. Even with a properly designed manifold, channeling will be most severe along the sides, where the sparge water will be inclined to take the shorter path of slipping down the smooth sides of the cooler wall toward the manifold rather than navigating through the grain bed.

This problem can be avoided by placing the manifold tubes away from the walls. In a rectangular cooler, the distance between the outer manifold tubes and the cooler wall should be half that of the manifold tube spacing, or slightly greater (see the box, “Manifold Designs.") It is also a good idea not to slot the short, transverse tubes at either end in a rectangular cooler because of their proximity to the walls. The longitudinal slotted tubes dissecting the center of the cooler adequately cover the floor area without the help of the transverse tubes. The same guidelines apply to a circular cooler, except that the tubes nearest and opposite the drain (or the circular tube) can be slotted so long as they aren’t too near the wall.

Likewise, the slots should face up or to the sides and away from the bottom to help prevent water from channeling along the floor. (Some brewers opt to face the slots down to avoid getting them clogged with grain, but I have not found that to be a problem.)

No Sweat

And there you have it. Simply collect your wort, dump the spent grain in the compost pile, and begin your boil: You’re on your way to your first (or first improved-system) all-grain beer.

With the picnic cooler approach, the transition to all-grain brewing needn’t be difficult nor exceptionally expensive. Insulated coolers provide good temperature control, easy-to-clean surfaces, and convenient handles; they ideally demonstrate that with a little ingenuity you can save yourself time and money as you turn what could have been a chore into a personal accomplishment.