BrewingTechniques
The Basics of Building a Picnic-Cooler Mash/Lauter Tun
Tools and Materials: Adjustable wrench
Drill and/or a hacksaw
Silver solder (plus liquid flux and a propane torch)
8 ft. of 1/2-in. or 3/8-in. soft or rigid copper tubing or CPVC plastic piping
4 elbows
5 tee sweat fittings

Six Simple Steps

  1. Create a drainage hole. Unless your cooler already has a drainage hole, drill one into the cooler close to the bottom of the cooler.

  2. Install the valve. Insert a bulkhead fitting and valve. Plastic bulkhead fittings are increasingly available at homebrew shops. If you are mechanically inclined, they can also be made from brass pipe and other hardware for just a few dollars. You can use a standard brass pipe nipple to pierce the cooler wall and then cut extra threads on the nipple with a standard thread-cutting die as necessary to enable the nut and washer to snug up to the wall.

    The washer or gasket that is used for a bulkhead fitting needs to be able to withstand the high temperatures of the mash and must be made of a material that won't contribute any off-flavors. Rubber washers are available from hardware stores. The solid backing washer needs to be soldered into place to prevent water from leaking along the threads of the pipe. This type of washer maintains a tight seal when attached to a single gasket mounted inside the vessel.

    Important: Be sure to place the sealing washer against the inside wall to prevent wort from becoming trapped between the inner and outer walls of the cooler (trapped wort becomes a potential breeding ground for contaminants).

    A good stopcock or ball valve is essential to prevent leaks and contamination. Use a valve designed specifically for liquids, not for natural gas; gas valves tend to trap wort internally, leading to bacterial contamination in future batches. The valve balls for liquids are typically made of brass with stainless steel or chrome-plated ball mechanisms. Ball valves allow good control of flow rate. Stopcocks are commonly available in nylon or polypropylene and work best with vinyl hose systems; the metal ball valves work best with metal tubing.

  3. Construct the manifold. Connect the segments either by soldering (rigid) or with compression fittings (soft). diagram showing connections to solderSolder the connections indicated at left, but leave the other connections for the straight tubes free. This allows easy disassembly for removal and cleaning. Space the tubes in such a way that they discourage sparge water from channeling down the walls of the cooler. This can be accomplished by leaving less spacing between the outer perimeter tubes of the manifold and the wall of the cooler than you would for spacing between the individual tubes (see the box, "Manifold Designs").

  4. Add the slots or holes. Saw slots or drill holes in the tubing approximately 1/2 in. apart and no more than halfway through the tubing. The holes should be 1/16 in. to 3/32 in., as from a standard hacksaw. Arrange the slots or holes so that they face upwards, away from the bottom of the cooler.

    Illustration of pipe

  5. Attach manifold to drain setup. Use a hose barb fitting, a compression fitting, or a threaded fitting.

  6. Clean. Clean all copper and brass fittings with white distilled vinegar (5% acetic acid) before assembly. Be sure to thoroughly rinse away any remaining flux after soldering.

Spigot hole illustration 1

One method for securing the manifold outlet through the cooler spigot hole is shown above. Plastic- or brass-threaded bulkhead fittings can also be used (below).

Spigot hole illustration 2

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Manifold Designs
The manifold should fit the bottom of the cooler, cover the most area possible, and not move around.

Illustrations of cylindrical cooler manifold design options Design options for a cylindrical cooler:
Note that the wort at Point "A" in the first figure has a comparatively long distance to travel to the drain. Either Design #2 or #3 will work well. To avoid channeling effects in the circular design, the distance "y" from the outer ring to the cooler wall should be greater than the distance "x," which represents a point equidistant from the center point of the manifold and the outer ring.

Illustrations of rectangular cooler manifold design options Options for rectangular coolers:
The manifold on the left could be improved by providing a more direct means for wort at Point "A" to reach the drain. The middle design is better, but Design #3 has more collection area and less distance for the water to travel to get to the drain. Note that the distance between the side of the manifold and the cooler should be one-half the distance between the longitudinal tubes.

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Step Mashing in a Picnic Cooler
Multirest mashes require heat additions to step the mash temperature through the various enzyme rests. This process can be tricky in a picnic cooler because rather than simply heating the vessel to the desired temperature, you must instead add precisely calculated quantities of boiling water to achieve the desired temperatures (see below). A further complication is that the thermal mass of the mash increases with each addition, and more and more water is needed at higher temperatures to continually raise the temperature.

Therefore, if your cooler is moderately sized for your mash, you need to start out with a stiff mash (perhaps even as low as 34 qt/lb of grain) to leave yourself enough volume for the additional water. Even then, only two temperature rests are usually possible, but you can achieve a third rest if the change in temperature is only a few degrees.

You need to decide whether the additional work is desirable, or even necessary, for your recipes. Review Jim Busch's article on step mashing on page 26 to help make the determination. It's probably best to get a real handle on the single-infusion mash before diving into further manipulations.

Calculating Water Additions for a Step Mash
This calculation is based on calorimetry and thermal equilibrium. By determining the amount of heat provided by a volume of hot water we can predict how much that heat will change the temperature of the mash. The basis for this calculation is the first law of thermodynamics, which assumes that no heat will be lost to the surroundings.

The factors used in the following equation are rounded to single digits to make the math simpler. The difference between these and more precise figures is at most a cup of hot water and less than 1 F. The equation presented here has been algebraically simplified, including conversion of the mass of hot water to volume. All temperatures must be in degrees Fahrenheit. Experience has shown the equation to be fairly reliable, even if it may be a few degrees off in its prediction, depending on the mash tun. It will be consistent if the mash tun is preheated in the same manner for each batch.

Performing your step mash:
You can tackle the initial infusion in two ways. You could use the seat-of-the-pants infusion approach described in the main text for the initial wetting (that is, guessing the proper strike water temperature to be 10-15 F above the target mash temperature). Measure your resulting temperature and proceed with the infusion equations from there.

Or, use the simplified equation provided here to arrive at the proper strike water temperature. When mixing hot water with dry grain, the amount of grain does not matter, only its temperature.

Initial infusion equation:

Strike water temperature (Tw) = (0.2 R) X (T2 - T1) + T2

Mash infusion equation:

Wa = (T2 - T1) X (0.2G + Wm) (Tw - T2)

where:

Tw =  the actual temperature of the infusion water
R =  the ratio of water to grain in quarts per pound
T1 =  the initial temperature of the mash (or dry grain)
T2 =  the target temperature of the mash
Wa =  the amount of boiling water added (in quarts)
Wm =  the total amount of water in the mash (in quarts)
G =  the amount of grain in the mash (in pounds)

The infusion water does not have to be boiling; the nominal sparge water temperature of 170 F (77 C) will also work, which means that the Tw becomes 170 F, and more water (Wa) will be needed to make up the additional quantity of heat.

Example
This example pushes the envelope with three rests. Suppose we plan to mash 8 lb of grain through a 104 F, 140 F, and 158 F (40 C, 60 C, and 70 C) multirest mash schedule. For the purposes of this example, we will assume that the temperature of the dry grain is 70 F (21 C). The first infusion will need to bring the temperature of the mash from 70 F to 104 F. We will start with an initial water ratio of 1 qt/lb. Using the initial infusion equation, the strike water temperature is:
Tw = (0.2 R) X (T2 - T1) + T2
Tw = (0.2 1) X (104 - 70) + 104 = 110.8, or 111 F

For the second infusion, to bring the temperature to 140 F, we need to use the mash infusion equation. At 1 qt/lb, Wm is 8 qt. We will assume that our boiling water for the infusions has cooled somewhat to 210 F.

Wa = (T2 - T1) X (0.2G + Wm) (Tw - T2)
Wa = (140 - 104) X (1.6 + 8) (210 - 140)
Wa = 36 X 9.6 70 = 4.9 qt

For the third infusion, the total water volume is now 8 + 4.9 = 12.9 qt.

Wa = (158 - 140) X (1.6 + 12.9) (210 - 158)
Wa = 18 X 15.1 52 = 5.2 qt

The total volume of water required to perform this schedule is 8 + 4.9 + 5.2 = 18.1 qt, or 4.525 gallons). The final water-to-grain ratio has increased to 17.9 8 = 2.2 qt/lb.

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