Lautering for All-Grain Brewers
Lautering appears to be a simple step in all-grain brewing. We run hot water through our grain bed after the mash step to extract the wort we need, and then proceed to boil, chill, and ferment that wort into beer. However, there are a lot of important processes happening during the lauter that determine the gravity, volume, and quality of our wort and finished beer.
In this article I’m going to break down lautering including important equipment design and process factors. Knowledge of these factors can help you get more efficiency out of your system, as well as hit your target gravities and volumes every time.
Mash Efficiency and Brewhouse Efficiency
When we talk about the mashing process as a whole, many brewers focus on the efficiency of the mash process. Mash efficiency measures the percent of potential grains by weight converted into gravity points in the extracted wort. It is distinct from brewhouse efficiency, which measures the overall percentage of gravity points that make it into the fermenter. Brewhouse efficiency is lower than mash efficiency because it includes losses that occur later in the brewing process.
Mash efficiency is calculated totaling the weight times the potential/yield points for each grain, which is typically listed as the dry grain fine yield. The yield represents the highest possible percentage of sugars by weight you could extract under laboratory conditions. Potential is another measure for the yield, and usually expressed as a specific gravity representing the gravity from a pound of grain into a gallon of water. These are the same measure, but expressed in different units. Using either measure you can calculate the potential gravity points for a given grain bill, which you then divide into the volume to get the estimated ideal gravity of the wort.
In the real world, no one achieves the ideal extraction during the mash, which would be 100% efficiency. The percentage of the ideal you achieve is called the mash efficiency, and is often in the 80–85% range for homebrew systems. If we include other losses in the system as we go from lauter tun to fermenter, the efficiency drops further and the percent we achieve going into the fermenter is called the brewhouse efficiency. This number is typically in the 65–75% range for many homebrewers.
I will also note that having an optimal mash or brewhouse efficiency is not as important for homebrewers as it is for commercial brewers. At a homebrewer level, a 5% lower efficiency might mean only an extra pound (0.45 kg) of grain is needed to get to our target gravity, which is a nominal expense of a dollar or two for most homebrewers. However, at a commercial level a 5% increase in efficiency would mean 5% less grain costs over an entire year, which could be a substantial savings. So we don’t need to be obsessive about our homebrew system efficiency even though as brewers we want a system that
is effective.
Lauter Tun Design Considerations
A lauter tun is simply a vessel designed to hold the grains while lautering and filter out the grain matter from the wort. Ideally it will also extract as much of the color and sugars as possible from the grains, which will improve our mash efficiency. In most modern brewing systems the mash tun doubles as the lauter tun, so we often mash and lauter in the same vessel.
The lauter tun should be designed to maximize efficiency. It is important to understand, first, that the sparge operation is a diffusion process rather than a rinsing process. We’re not simply rinsing the sugars out of the grains, but instead giving the water a chance to dissolve those sugars into solution creating wort. This does take some time so it is important not to rush your sparge.
The grain bed is composed of grain particles, sugars, and grain husks. The grain husks help to form a natural filter bed that aids in extraction. The mashed sugars are mostly soluble, which aids in extraction. Unfortunately the grain bits are not uniform in size, and their variation leads to instabilities in flow and a loss of some efficiency.
One of the first design considerations is the width and height of the lauter tun. It might appear at first that a high, narrow lauter tun would be more efficient because the water would have to flow more slowly through a thicker grain bed. In reality it turns out that if the grain bed is too tall it will actually compact down due to weight, and inhibit the flow. Similarly if the grain bed is too shallow, the grain filter bed will never form and the wort will not properly clear.
At the homebrew level, the rule of thumb is that the grain bed height-to-width ratio should be between 1:2 and 2:1.1 Assuming a cylindrical lauter tun, this means in practice the height of the lauter tun should be at least as high as the diameter of the lauter tun. Keep in mind that the rule of thumb above is for the grain bed itself and we’ll always need additional height to account for water added when sparging to maintain a floating grain bed as well as the fact that our lauter tun needs to account for variation in the grain bill to support high-gravity batches. Both of these factors drive most lauter tuns to be closer to a 2:1 height-to-width in practice.
A second major consideration in lauter tun design is the flow of the wort through the grain bed. Water will always choose the path of least resistance, and as noted earlier variations in the crush will form natural channels through the grain bed, extracting more sugars from some parts of the grain bed than others.
The filtering system we use at the bottom of the lauter tun can potentially make these channels much worse. Consider for a moment a lauter tun with a single small hole in the middle of the bottom of the vessel. All of the wort would need to pass through that one hole, creating a single channel that excludes a large portion of the grain bed, resulting in very poor efficiency. It would also be excruciatingly slow, as all of the wort would have to travel through a single small hole.
As we add more holes and expand the area covered, more channels will form, and the efficiency will rise. For example a manifold pipe in the bottom of the grain bed with dozens of holes will certainly work better than a single hole. A full screen filter bed with hundreds of holes that covers the entire bottom of the lauter tun is ideal, as potentially hundreds of channels are created covering most of the grain bed area.
Another design consideration is the dead space under the filter bed. As long as the system is designed to recover this dead volume, it won’t have a significant impact on efficiency. However, if you are mashing in the same vessel as you lauter, then the dead volume needs to be considered as it will alter the water-to-grain ratio in the mash and could leave you with less water in the grain bed above the filter. So if you have a mash tun with a large dead space, you may need to use more water in the mash to achieve
your desired water-to-grain ratio.
A final consideration for lautering is how to feed your sparge water into the grain bed from the top. This is, in many ways, analogous to the filtering design issues mentioned earlier. If we imagine adding hot water to the lauter tun from a single point, it is not hard to see that this can form a single channel through the grain bed resulting in low efficiency. Ideally we want to distribute the water evenly across the top of the entire grain bed without disturbing the grain bed itself.
It is for this reason that many commercial and advanced homebrewing systems use a sparge arm that rotates to evenly distribute sparge water over the top of the grain bed. Others use a spray nozzle to get a similar effect. I also try to keep my grain bed floating during the entire sparge by regulating the flow of water in and out of the lauter tun.
Process Considerations
With an understanding of the design considerations of the lauter tun, we now turn to some of the process factors that drive lautering.
Grain crush size
Perhaps the most important of these is getting a proper grain crush up front. As I mentioned earlier, the grain husks form a filter bed that helps to form tiny channels that prevent the water from running straight through the bed. These husks also prevent the small bits of grain from clogging up your filter screen, which would result in a stuck sparge.
An ideal grain crush has large, partially intact grain husks but very small bits of the malt’s endosperm from the interior of the seed. In most cases a dual roller mill is needed to achieve this proper crush as the rollers will crush the interior of the grain but leave large intact pieces of husk. You would like to have the interior bits be as small as possible without destroying the husk pieces or resulting in a stuck sparge.
To do this you need to adjust your malt mill gap carefully, and experiment with your specific system as different systems have slightly different size filter bed holes and layouts. This means that some systems may handle a finer grain crush than others. Ideally you want to crush your grains as fine as possible without creating a stuck sparge situation.
Mash and sparge volumes
A second process consideration is getting your mash and sparge volumes correct. The volume of water needed for the sparge is driven by the total mash water needed. First, your pre-boil volume is critical as that determines the total amount of wort you need to extract in the lautering process. This volume can be calculated by taking your desired batch volume into the fermenter and adding to it your boil-off volume and losses (trub loss being the major one).
To your pre-boil volume you need to add the grain absorption, which is the amount of water that will be absorbed by the grain itself. This is typically around 1 pint of water per pound of grain (approximately 1 L/kg). BeerSmith uses 0.96 pints per pound of grain (1 L/kg) as the default. Brew-in-a-bag (BIAB) brewers achieve more grain bed compression, and typically a number of about 6 fl. oz./lb. (0.4 L/kg) is used, though obviously there is no lauter step with a BIAB system.
Adding together your target pre-boil volume to the grain absorption and also any dead space (losses) in the lauter tun will give you the volume needed for total mash water used. From there it is a matter of dividing the total mash water between the mash and sparge.
Usually the mash portion is determined by the water-to-grain ratio you want to use for the mash itself. Most modern mashing is done in the 1.2–1.7 quarts per pound range (2.5–3.5 L/kg). So determining the mash water needed can be calculated directly from the weight of all of the grains used in the mash. Finally, take your total mash water needed and subtract the mash portion to get the water needed in the sparge. This is the volume you will heat up separately for the sparge step.
Temperature and the mash out
Another consideration for lautering is what temperature to use as well as whether to include a mash-out step. A higher temperature will decrease the mash viscosity, which can aid in extraction. Hotter sparge water will make the sugars in the grain more soluble and easier to dissolve. In addition the hotter water is less viscous, which also helps to reduce the chance of a stuck sparge, particularly when working with non-barley adjuncts.
Some older references include a warning about getting the mash water too hot (about 180 °F/82 °C is often cited) as it could result in excess tannin extraction during the sparge. In reality, assuming a proper pH, a higher sparge temperature does not increase the risk of tannin extraction, so you can add near-boiling water in the sparge, which will raise the overall temperature of the mash bed and increase viscosity.
The Brülosophy blog did an experiment on “cold sparging” with room-temperature water. They compared a beer lautered at conventional temperatures versus one that was lautered with cool water. While they did get a slightly higher original gravity (better extraction) in the batch that was hot sparged, blind taste tests between the hot sparge and cold sparge beer found no difference in the overall flavor of the beer.2
Which brings us to the decision on whether to use a “mash-out” step. The purpose of a mash-out step is to raise the temperature of the grain bed up to about 168 °F (76 °C) to halt enzymatic activity and decrease viscosity. In reality, enzymatic activity does not have a hard cutoff temperature, and you really don’t need to “halt” it after conversion, as it will certainly be curtailed in the boil. So the main reason to do a mash out would be to decrease viscosity and increase solubility of extract in the wort. This is primarily needed when working with sticky non-barley adjuncts like wheat to avoid a stuck sparge. So the rule of thumb I use is to do a mash out when my grain bill has a large portion of non-barley adjuncts.
The decreased viscosity and increased solubility of extract in the wort caused by the mash out may also improve efficiency, especially for high-gravity beers. Also it reduces the time needed to bring the wort up to a boil. Doing a cold sparge will lower the overall wort temperature, so it will take much longer to achieve a rolling boil as you transition to the boil phase.
Lautering time
How long should you lauter? As I mentioned in the section on lauter tun design, lautering is a diffusion process and not a rinsing process, so ideally you want to lauter slowly. I typically will take at least 20–30 minutes to lauter my mash, and sometimes run slower if working with sticky non-barley grains.
I also regulate the flow in and out of the lauter tun to maintain a floating grain bed. By keeping the grains floating until the very end of the lauter, you avoid compacting the grain bed too much, which can result in a stuck mash or poor efficiency.
The pH of the runnings
While most homebrewers do not need to worry too much about the pH of the runnings, commercial brewers often do monitor the pH of the wort as it comes out of the lauter tun. The pH will start close to the pH of the mash (5.2–5.6 is recommended) but will rise as more alkaline water is run through the acidic grain bed. For light-colored, lower-gravity beers in particular the pH can rise fairly rapidly near the end of the lautering process.
If the pH of the runnings rises above 6.0 you run the risk of extracting tannins from the grain husks in the grain bed. Tannins can create a bitter, sour off-flavor akin to sucking on a tea bag. For this reason most commercial brewers will stop lautering when the pH of the runnings exceeds 6. For homebrewers, this is rarely an issue as long as your starting mash pH is adjusted down to the 5.2–5.6 range, but can be an issue for some low-gravity, light-color beers.
The vorlauf and recirculation
The traditional lautering process begins with a step called the vorlauf. This is a German name for drawing off the first bit of runnings (generally a couple quarts/liters for a 5-gallon/19-L batch) from your sparge and adding it back to the top of the mash tun. This is done to give the grain bed a chance to set and also remove the large number of grain bits and debris that come out initially during the sparge, improving clarity. It also moves water to the top of the grain bed and avoids diluting wort in the kettle. I do recommend using a vorlauf step if you are doing a traditional lauter.
Many modern brewing systems and even many small all-in-one systems now incorporate a pump for recirculating the wort during the mash. This is similar to the vorlauf step, but often the pump runs continuously until the lauter begins.
Recirculation has some benefits. It sets the grain filter bed early so you have an established bed when you begin the lautering process. It also aids in clarity, as you won’t get the initial wave of grain bits and debris when you start sparging.
The only downside of continuous recirculation is that it can set up channels in the grain bed, which may ignore or bypass some portions of the grain bed. This is particularly true if the system recirculates the wort out to a single fixed point in the top of the grain bed rather than distributing it across the grain bed with a sparge arm or similar device or if the recirculation rate is too fast. This can result in a drop in efficiency, as the wort will flow through the established channels instead of flowing evenly through the entire grain bed.
High-gravity beer considerations
While I’ve covered all of the major factors in lauter tun design and the process by this point, I want to also address the special case of high-gravity lautering. When you brew a high-gravity beer, your efficiency will drop off substantially. The reason for this is simply that you have roughly the same quantity of overall water for the batch running through a much larger quantity of grain.
As I mentioned earlier, lautering is a diffusion process where the sugars we converted during the mash dissolve into the water forming wort. Unfortunately, as the gravity of the wort goes up it becomes increasingly difficult to put more sugar into it. In effect it becomes more difficult for the wort to absorb additional sugars as the gravity rises. So having a larger amount of grains in roughly the same amount of water (driven by our desired pre-boil volume) results in lower overall efficiency.
You need to account for the lower efficiency by using even more grain, which to some degree makes the problem worse. In some cases you will need more grain than may fit in your mash tun, and may need to move to other techniques like adding malt extract during the boil to hit your original gravity or brewing smaller batch sizes. However, you can improve your high-gravity efficiency by raising the temperature during the sparge, because hot water will make the sugars more soluble.
Therefore doing a mash out and high-temperature sparge is a good idea when brewing a high-gravity beer. In addition, you will need to lower your mash and brewhouse efficiency when brewing big beers to account for the lower efficiency achieved. Many brewers maintain two separate equipment profiles for regular brewing and high-gravity brewing to account for these factors.
Summary
Though lautering may sometimes be looked at as simply “rinsing” the grains, the actual process is a bit more complex than that. Achieving an efficient lauter involves selecting a well-designed mash and lauter system, properly crushing the grains, selecting the right temperature, sparging slowly, managing the flow in and out of the lauter tun, and monitoring the pH of the runnings. Additional care must be taken with high-gravity beers to make sure you don’t overflow the capacity of your mash tun and achieve good extraction. Follow these tips and reap the rewards.
Resources:
1 Palmer, John. How to Brew. Brewers Publications
2 Found, Ray. Impact Sparging with Cool Water Has on an American Amber Ale https://brulosophy.com/2016/04/11/
