Chapter 17 - Getting the Wort Out (Lautering)
17.2 Getting the Most From the Grainbed
The grainbed can be a few inches to a couple feet deep, but the optimum depth depends on the overall tun geometry as well as the total amount of grain being mashed. A good rule of thumb is: "The depth of the grainbed should be no less than one half the shortest dimension of the floor area, nor greater than twice the longest." In other words, the grainbed aspect ratio can vary between 1:2 and 2:1. If the grainbed gets too shallow, i.e., from lautering too little grain in too large a tun, then an adequate filter bed won't form, the wort will not clear, and you will probably get hazy beer. A minimum useful depth is probably about 4 inches but a depth of between 8-18 inches is preferable. In general, deeper is better, but if it is too deep, then the grainbed is more easily compacted and may not let any wort through, making lautering nearly impossible.
Recalling Chapter 12, extraction efficiency is determined by measuring the amount of sugar extracted from the grain after lautering and comparing it to the theoretical maximum yield. In an optimum mash, all the available starch is converted to sugar. This amount varies depending on the malt, but it is generally 35-ish points per pound per gallon for a 2 row barley base malt. This means that if 1 pound of this malt is crushed and mashed in 1 gallon of water, the wort would have a specific gravity of 1.035. Most brewers would get something closer to 1.031. This difference represents an extraction efficiency of 88%, and the difference could be attributed to poor conversion in the mash, but it can often be explained by lautering inefficiency.
Let's think about the grainbed it is composed of grain particles, sugars and insoluble grain husks. In an ideal world, the particles would all be small and finely divided with an equal spacing between them and would be equally well rinsed. Of course, this isn't the case. The grain particles vary quite a bit in size and this variation leads to regions of greater density within the grainbed. Since fluids always follow the path of least resistance, this leads to a problem of preferential flow through the grainbed causing some regions of grain to be completely rinsed and other regions to not be rinsed at all.
Our goal in the lautering process is to rinse all the grain particles in the tun of all the sugar, despite all of the non-ideal conditions. To do this we need to focus on two things:
keeping the grainbed completely saturated with water, and making sure that the fluid flow through the grainbed to the drain is slow and uniform.
By keeping the grainbed covered with at least an inch of water, the grainbed is in a fluid state and not subject to compaction by gravity. Each particle is free to move and the liquid is free to move around it. Settling of the grainbed due to loss of fluidity leads to preferential flow (a major cause of poor extraction) and can result in a stuck sparge.
The more uniformly the water moves through the grainbed, the more sugar it can extract from the grain. This results in better extraction efficiency. Fluid flow through the grainbed is complex and depends greatly on the design of your lauter tun.
The original (at least the most popularized) home lautering system was probably the bucket-in-a-bucket false bottom championed by Charlie Papazian in The Complete Joy of Homebrewing (1984). 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. False bottom systems usually rinse the grainbed uniformly, but there are two drawbacks that need to be considered. The first is that the placement of the outlet hole in the outer bucket influences the way the tun drains. More rinsing will occur on the side of the grainbed where the hole is. For best results, the outlet tube needs to be extended to the center of the tun so that it will drain evenly. Secondly, false bottoms have the potential to flow too fast because of the very large drainage area available and can compact the grainbed as a result. Stuck sparges from draining too fast are a common problem for homebrewers using false bottoms for the first time.
Picnic coolers offer a few 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 the hour, and then draining the sweet wort.
Figure 88- Rectangular Cooler Mash/Lauter Tun showing top and end views of the cooler along with a detail of the slotted manifold pipe. (The other thing is the lid.)
Coolers offer two options for lautering: they can accommodate traditional false bottoms or use a simple slotted-pipe "manifold" system. Ready-made false bottoms (e.g. Phil's Phalse Bottom - Listermann Mfg.) are available for some coolers, but you can also build a slotted pipe manifold for just a few dollars. 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 $40. Everything you need to build one of these tuns is readily available at a hardware store.
Manifolds are less likely to allow the mash to become compacted during lautering, resulting in a stuck sparge, in which water will not flow through the grain bed. This brings us to the question-- what is the optimum outflow rate? There is a trade-off: if you lauter too quickly you will collect a lot of wort but have a low extraction, if you lauter too slowly you will have great extraction but you will take all day to do it. Most homebrewers use the rule of thumb of 1 quart per minute. If your extraction is low, i.e. less than 28 points/pound/gallon, you should try a lower flow rate. The best way to control your flow rate by using a ball valve or stopcock on the outflow.
Another extraction efficiency problem that needs to be considered when designing your tun is preferential flow down the walls. The smooth space between the grainbed and the wall of the tun can be the path of least resistance to the drain. To minimize this short circuiting, false bottoms should fit tightly and manifold tubes should be spaced so that the distance from the outer tubes to the wall of the tun is half of the inner tube spacing (see Figure 88). For example, a manifold with a tube spacing of 6 inches should have 3 inches of space between the manifold and the adjacent walls. Preferential flow is more of a concern in false-bottom systems because a loose fitting false bottom with a gap at the wall presents a unobstructed flow path to the drain.
It may be difficult to visualize how all of these guidelines combine to help you lauter efficiently, so let's summarize:
- Maintain an inch of water over the grainbed during the lauter to assure fluidity and free flow.
- Regulate the flow with a valve to assure the best extraction and prevent compacting the grainbed.
- When designing your lauter tun for more uniform flow, either:
- Make sure the false bottom fits well and that the outlet tube is centered. (False Bottom System)
- Space the manifold tubes away from the walls. (Manifold system)
More instructions and design details for building a mash/lauter tun from a cooler are given in Appendix D. I also elaborate on how to design the manifold for the most uniform flow through the grainbed.
In the next chapter we will get your feet wet (probably literally). I am going to walk you through your first all-grain mash from start to finish. I will describe some extra equipment you will probably need and then we will get started. Complete instructions for building a mash/lauter tun from a picnic cooler are given in the Appendix.
Richman, D., personal communication, April, 1995.
Palmer, J., Prozinski, P., Fluid Dynamics - A Simple Key to the Mastery of Efficient Lautering, Brewing Techniques, New Wine Press, Vol. 3, No. 4, 1995.
Gregory, G., personal communication, 1998.