Sizing the Tun
To figure out just how many pipes your manifold needs, you will need to measure your cooler, and to pick a cooler you need to figure out the volume of your typical mash. My advice is to pick your cooler based on your average batch; don't pick a larger one than you really need, thinking that a larger one will give you more flexibility for future batches. If you pick one that is too large for the majority of your batches, your grainbed depth will be too shallow and your extraction will suffer. Table 21 lists the volume of 1 pound of grain being mashed in 1 quart of water. This is usually the minimum ratio most brewers would use and it is fully saturated i.e. increasing the water to grain ratio only adds the volume of the water to the total volume given for a ratio of 1:1.
So, you take your typical batch size (5) and multiply that by your typical OG (1.050) and determine how many pounds of grain that equals, using your typical yield (30) in pts. /lb. /gal. Thus, 5*50=250, and 250/30=8.3 lbs. At a ratio of (2) quarts per pound, the total volume of this mash would be 8.3*(42+32)=616.6 fluid ounces or (dividing by 128) 4.8 gallons. So, I would recommend either the 24 quart rectangular or the 5 gallon cylindrical.
Table 21 - Volume of Unit Mash
Volume at Mash Ratio
Volume of Grain Alone
@ 1 qt/lb. = 42 fluid oz.
10 fluid oz.
@ 1l/500g = 1.325 liters
Table 22 - Picking your cooler.
The conversion factor for cubic inches to gallons (U.S. liquid) is 231 cubic inches per gallon.
Common Cooler Sizes
Actual volume based on dimensions (gallons)
20 Quart Rectangular
7 x 11 x 12
24 Quart Rectangular
9 x 14 x 10
34 Quart Rectangular
10 x 16 x 10
48 Quart Rectangular
11 x 18 x 12
5 Gallon Cylindrical
9.5 x 18
10 Gallon Cylindrical
12.5 x 20
Here are the summary guidelines for designing efficient manifolds and lauter tuns:
- Have the straight line distance to the drain be as short as possible. In other words, orient the pipes longitudinally with respect to the drain.
- Deeper grainbeds have more uniform rinsing, all else being equal.
- The closer the pipe spacing, the more uniform the flow, all else being equal. A spacing of 6 inches is the maximum in my opinion. A spacing of 2-4 inches is preferred.
- The spacing of the pipes from the wall of the cooler should be S/2 or slightly greater to avoid preferential flow down the smooth walls.