Section 5 – Appendices
Appendix F – Lauter Tun Design for Continuous Sparging
Continuous sparging is all about understanding steady-state flow. We need to understand how the sparge water is going to flow through the grain bed, so we can predict where the grain will be rinsed of sugar and where it won’t be. Before I lead you through all the theory and explanations, let me cut to the chase and tell you how it works best:
● Use a false bottom or a large multi-pipe manifold to maximize coverage of the floor of the lauter tun.
● Regulate the flow with a valve to achieve a slow flow rate—no greater than 1 quart per minute—to prevent compacting the grain bed.
● Maintain an inch of water over the grain bed during the lauter to ensure fluidity and free flow.
To explain why false bottoms work best, I have to turn to fluid dynamics and some mathematical models that a friend put together for me. As I mentioned in the last appendix, I spent a year conducting fluid flow experiments with ground-up corncobs and food coloring in an aquarium in order to understand how slotted pipes worked under continuous sparging. Those experiments demonstrated that the flow converged to the pipe, and that all points along a slotted pipe drained at the same rate, regardless of distance to the drain. See Figure 195.
To explain these observations, I posted on the Homebrew Digest asking for someone with good math skills to contact me to help me figure out a model. A few weeks later I was picking up a hose barb at Home Depot and noticed a guy standing in front of the brass fittings with a cooler next to him. Turned out that he was an astrophysicist at Cal Tech, and he offered to check the library for a book on fluid dynamics. He found a book, read it, and put together a computer model based on Darcy’s Law and Laplace’s Equation that could quantify the flow in a lauter tun as a histogram. See the sidebar, “Fluid Mechanics.” As you may imagine, this came in handy for comparing manifolds and false bottoms. The next sections explain how we used the model to understand lauter tun flow.
Fluid Mechanics
To extract the wort from all regions of the grain bed, there must be fluid flow from all regions to the drain. In a perfect world, the wort would separate easily from the grain, and we could simply drain the grain bed and be done. But it is not a perfect world, and we must rinse or sparge the grain bed to get most of the sugars, and some sugar is still left behind. If some regions of the grain bed are far from the drain and experience only 50% of the sparge flow, then only 50% of the wort from those regions will make it to the drain. Fluid mechanics allows us to model the flow rates for all regions of the grain bed and determine how well a grain bed is rinsed. These differences can be quantified, enabling us to compare different lauter tun configurations.
To illustrate, let’s look at a cross section of a 10-inch-wide by 8-inch-deep lauter tun using a single pipe manifold. See Figure 196a. For every unit volume of water that rinses the grain bed, grain at the top of the grain bed will experience “unit” or 100% flow. As the flow moves deeper into the grain bed, it must converge to the single drain. This means that the region immediately above the drain can experience ten times the unit flow, while a region off to the side will only experience a tenth of the unit flow. A vector flow plot for two pipes in Figure 196b demonstrates the same behavior, although the convergence effect is less. Figure 197 shows the flow rate distribution for the single pipe manifold. For purposes of illustration, unit flow (the big white upper area) is drawn within the bounds of ±10% of actual unit flow, and lines for 50%, 90%, 110%, and 200% of unit flow are shown. Figures 196 and 197 convey the same idea, but Figure 197 lets us quantify the percentages of flow for this grain bed. A histogram (Figure 198) can be constructed from this data that summarizes the flow distribution, and we can use the histogram to measure two aspects of lautering performance—efficiency and uniformity. Figures 199 and 200 illustrate how these flows and histogram compare to a false bottom. The differences will be explored more fully in the next couple of sections, as we look at the concepts of lauter efficiency and uniformity.
To illustrate, let’s look at a cross section of a 10-inch-wide by 8-inch-deep lauter tun using a single pipe manifold. See Figure 196a. For every unit volume of water that rinses the grain bed, grain at the top of the grain bed will experience “unit” or 100% flow. As the flow moves deeper into the grain bed, it must converge to the single drain. This means that the region immediately above the drain can experience ten times the unit flow, while a region off to the side will only experience a tenth of the unit flow. A vector flow plot for two pipes in Figure 196b demonstrates the same behavior, although the convergence effect is less. Figure 197 shows the flow rate distribution for the single pipe manifold. For purposes of illustration, unit flow (the big white upper area) is drawn within the bounds of ±10% of actual unit flow, and lines for 50%, 90%, 110%, and 200% of unit flow are shown. Figures 196 and 197 convey the same idea, but Figure 197 lets us quantify the percentages of flow for this grain bed. A histogram (Figure 198) can be constructed from this data that summarizes the flow distribution, and we can use the histogram to measure two aspects of lautering performance—efficiency and uniformity. Figures 199 and 200 illustrate how these flows and histogram compare to a false bottom. The differences will be explored more fully in the next couple of sections, as we look at the concepts of lauter efficiency and uniformity.
Darcy's Law
For fluid flow through porous material, Darcy’s Law states that flow velocity is proportional to pressure variations and inversely proportional to the flow resistance. The resistance (or, inversely, the permeability) to flow is determined by the media—in our case, the grist. By combining this velocity/pressure relationship with a statement that water is conserved (i.e., water is not created or destroyed), we can form a numerical model that describes the fluid flow throughout the tun.
Darcy’s Law: u = -K/µ ∇ p
where p is the pressure (actually, the velocity potential), µ is the absolute (or shear) viscosity, K is the permeability, and u is the Darcean velocity (bulk flow velocity).
Conservation of water: ∇•∑•u = 0
Combination: ∇(squared)• p = 0 (Laplace’s equation)
Assuming K and µ are constant everywhere, this equation holds true everywhere except the top of the tun, where water is added, and the pipe slot, where liquor flows out of the tun. The tun walls are rigid (they can support any pressure), and nothing flows through the walls.
Darcy’s Law: u = -K/µ ∇ p
where p is the pressure (actually, the velocity potential), µ is the absolute (or shear) viscosity, K is the permeability, and u is the Darcean velocity (bulk flow velocity).
Conservation of water: ∇•∑•u = 0
Combination: ∇(squared)• p = 0 (Laplace’s equation)
Assuming K and µ are constant everywhere, this equation holds true everywhere except the top of the tun, where water is added, and the pipe slot, where liquor flows out of the tun. The tun walls are rigid (they can support any pressure), and nothing flows through the walls.
Efficiency
Earlier we stated that 50% of the unit flow rate would only extract 50% of the sugar. However, we cannot say that a 200% flow rate will extract 200% of the sugar. If we assume that 100% of the unit flow rate extracts 100% of the sugar, then there is no more sugar to extract, and higher flow rates do not extract anything further, except possibly tannins. If we add up all the extraction from the different flow regions of the grain bed, we can determine the efficiency percentage for that configuration.
For example, if a single pipe manifold system lautered 5% of the grain bed at 40% of unit flow, 10% at 60% flow, 15% at 80% flow, and 70% of the grain bed at 100% of unit flow or greater, the efficiency of that tun would be calculated as 90%:
(5 x 40 + 10 x 60 + 15 x 80 + 70 x 100 = 90%).
A “perfect” false bottom would lauter the entire grain bed with 100% of unit flow, because every region would have equal access to the drain, and would be 100% efficient. The computer model estimates a real false bottom (eighth-inch holes on quarter-inch centers) to be 99.7% efficient. (See Figure 200.)
For example, if a single pipe manifold system lautered 5% of the grain bed at 40% of unit flow, 10% at 60% flow, 15% at 80% flow, and 70% of the grain bed at 100% of unit flow or greater, the efficiency of that tun would be calculated as 90%:
(5 x 40 + 10 x 60 + 15 x 80 + 70 x 100 = 90%).
A “perfect” false bottom would lauter the entire grain bed with 100% of unit flow, because every region would have equal access to the drain, and would be 100% efficient. The computer model estimates a real false bottom (eighth-inch holes on quarter-inch centers) to be 99.7% efficient. (See Figure 200.)
Uniformity
While efficiency gives a measure of the extract quantity, the uniformity gives a measure of its quality. To discuss uniformity, we look at three percentages of flow: flow less than 90%, flow between 90 and 110%, and flow greater than 110%. With these three percentages, we can compare different configurations that have similar efficiency and determine if one configuration is more uniform than another. Flow values between 90 and 110% are considered “uniformly sparged,” with values less than 90% being undersparged and values greater than 110% oversparged. Generally, the percentage of oversparging is roughly the same as the percentage of undersparging for any one configuration.
Returning to our single pipe manifold example, let’s look at the histogram in Figure 197. From the histogram we can determine that only 56% of the grain bed is uniformly sparged, with 21% being undersparged and 23% over. This means 23% of the grain bed is subject to tannin extraction. But these percentages can be adjusted dramatically by tweaking a few variables.
Returning to our single pipe manifold example, let’s look at the histogram in Figure 197. From the histogram we can determine that only 56% of the grain bed is uniformly sparged, with 21% being undersparged and 23% over. This means 23% of the grain bed is subject to tannin extraction. But these percentages can be adjusted dramatically by tweaking a few variables.
Factors Affecting Flow
My thanks to Brian Kern, an astrophysicist and brewer from Cal Tech, who co-developed this material with me.
The computer model analyzed 5,184 configurations of lauter tun and manifold in order to determine the primary factors for flow efficiency and uniformity. In descending order, the factors are:
● interpipe spacing● wall spacing ● grain bed depth.
The analysis also determined that the pipe slots should always face down, being as close to the bottom as possible, because wort is not collected from below the manifold.
Interpipe spacing. By increasing the number of pipes across the width of the tun, you are effectively decreasing the interpipe spacing. Interestingly, analysis of the models (see Figures 202 to 205) showed a nearly linear relationship between pipe spacing and both efficiency and uniformity, which peaks at a center-to-center pipe spacing of four times the pipe diameter. For a half-inch pipe, maximum efficiency and uniformity occur at a center-to-center spacing of 2 inches. Although optimum, it is not necessary for the pipes to be that close; the relationship between spacing and efficiency/uniformity starts to flatten out at 3 inches, or six times the pipe diameter. As can be seen in Table 35, only 1 to 2% gains are realized by decreasing the pipe spacing from 3 to 2 inches, although when the grain bed is shallow (4 inches), the differences approach 5%.
The computer model analyzed 5,184 configurations of lauter tun and manifold in order to determine the primary factors for flow efficiency and uniformity. In descending order, the factors are:
● interpipe spacing● wall spacing ● grain bed depth.
The analysis also determined that the pipe slots should always face down, being as close to the bottom as possible, because wort is not collected from below the manifold.
Interpipe spacing. By increasing the number of pipes across the width of the tun, you are effectively decreasing the interpipe spacing. Interestingly, analysis of the models (see Figures 202 to 205) showed a nearly linear relationship between pipe spacing and both efficiency and uniformity, which peaks at a center-to-center pipe spacing of four times the pipe diameter. For a half-inch pipe, maximum efficiency and uniformity occur at a center-to-center spacing of 2 inches. Although optimum, it is not necessary for the pipes to be that close; the relationship between spacing and efficiency/uniformity starts to flatten out at 3 inches, or six times the pipe diameter. As can be seen in Table 35, only 1 to 2% gains are realized by decreasing the pipe spacing from 3 to 2 inches, although when the grain bed is shallow (4 inches), the differences approach 5%.
Figure 201 – Pipe to wall spacing geometry.
Wall spacing.
The next most significant factor is the spacing of the pipes with respect to the walls of the tun. There are three ways to do this (see Figure 201).● Edge spacing—the two outermost pipes are placed flush against the walls, and any other pipes are spaced evenly between them.● Even spacing—the spacing between the outer pipes and the walls is the same as the interpipe spacing.● Balanced spacing—the spacing between the outer pipes and the walls is half of the interpipe spacing.
As you can see in Table 36, balanced spacing is the most efficient. This spacing places the wall at half of the interpipe spacing, so that flow velocity is symmetrical around every pipe in the manifold, and the manifold draws as uniformly as possible from the grain bed. Another way of looking at this variable is to say that balanced spacing covers the greatest area, with the closest interpipe spacing, using the least number of pipes, for a given tun width. This factor is most significant for large interpipe spacings; at closer spacings, the uniformity difference between balanced and edge spacing is smaller (5% or less). But with edge spacing, you need to be aware of the propensity for preferential flow down the walls to the drain. This phenomenon is often referred to as “channeling.”
Fluid mechanics describes a “boundary effect,” in which the flow resistance decreases at the wall, due to a lack of interlocking particles, as a function of particle size. The boundary layer for crushed malt is about ⅛-inch wide. Likewise, if the edges of a false bottom do not conform to the tun walls, the flow will divert into the gaps. These low-resistance paths can result in some percentage of the sparge water bypassing the grain bed, which decreases the yield from each volume of wort collected. This implies that balanced spacing is preferable to edge spacing for manifolds, and false bottoms should be fitted closely to the tun to minimize the effect.
Fluid mechanics describes a “boundary effect,” in which the flow resistance decreases at the wall, due to a lack of interlocking particles, as a function of particle size. The boundary layer for crushed malt is about ⅛-inch wide. Likewise, if the edges of a false bottom do not conform to the tun walls, the flow will divert into the gaps. These low-resistance paths can result in some percentage of the sparge water bypassing the grain bed, which decreases the yield from each volume of wort collected. This implies that balanced spacing is preferable to edge spacing for manifolds, and false bottoms should be fitted closely to the tun to minimize the effect.
Grainbed Depth
The depth of the grain bed is the final significant factor—not the total depth of the grain and sparge water, only the depth of the grain itself. For both false bottoms and manifolds, the amount of flow convergence depends only on the drain size and spacing. The size of the convergence does not change significantly with depth (pressure). The ratio of underflow, uniform flow, and overflow within the convergence zone are nearly constant, and the size (height) of the convergence zone is nearly constant. In the case of false bottoms, the drain features are quite small, so the convergence zone is narrow (less than a half-inch, in our model). But the drain features of manifolds are larger and more spread out, so the convergence zone is large and affects a larger proportion of the mash.
In other words, increasing the grain bed depth changes the proportion of the grain bed that is outside the convergence zone, which increases the proportion of uniform flow, which increases the extraction efficiency as a whole. Thus, the efficiency of false bottoms (small zones) are not significantly affected by grain bed depth, while manifolds (large zones) are, although you can minimize it by decreasing the pipe spacing to reduce the height of the convergence zone.
For example: If you had only one pipe in a 10-inch-wide tun with an 8-inch-deep grain bed, the convergence zone is about 3.5 inches deep, and the percentage of uniform flow is 55.7%. If the grain bed is 48 inches deep, the convergence zone is still about 3.5 inches, but the percentage of uniform flow is now 92.5%. With 5 pipes, the zone height is 0.5 inches, and 90% of the flow is uniform at 8-inch depth. When you build a manifold lautering system, both the pipe spacing and wall spacing affect the actual size of the convergence zone, and the grain bed depth affects its relative size. To get the best performance from a manifold system you should optimize all three factors.
To summarize:● Design the manifold to have an interpipe spacing of 2 to 3 inches, closer to 2 being better.● Use balanced spacing to get the best results with the fewest pipes.● Choose a cooler that will give a good grain bed depth for your typical batch. I recommend a depth of 4 to 12 inches.
The following four plots summarize the analysis of all the numerical models for pipe spacing, wall spacing, and depth for half-inch diameter pipes. Each plot shows the behavior of the stated quantity as a function of center-to-center pipe spacing, and as a function of grain bed depth. The relationships are nearly linear except at close pipe spacings and shallow grain bed depths.
In other words, increasing the grain bed depth changes the proportion of the grain bed that is outside the convergence zone, which increases the proportion of uniform flow, which increases the extraction efficiency as a whole. Thus, the efficiency of false bottoms (small zones) are not significantly affected by grain bed depth, while manifolds (large zones) are, although you can minimize it by decreasing the pipe spacing to reduce the height of the convergence zone.
For example: If you had only one pipe in a 10-inch-wide tun with an 8-inch-deep grain bed, the convergence zone is about 3.5 inches deep, and the percentage of uniform flow is 55.7%. If the grain bed is 48 inches deep, the convergence zone is still about 3.5 inches, but the percentage of uniform flow is now 92.5%. With 5 pipes, the zone height is 0.5 inches, and 90% of the flow is uniform at 8-inch depth. When you build a manifold lautering system, both the pipe spacing and wall spacing affect the actual size of the convergence zone, and the grain bed depth affects its relative size. To get the best performance from a manifold system you should optimize all three factors.
To summarize:● Design the manifold to have an interpipe spacing of 2 to 3 inches, closer to 2 being better.● Use balanced spacing to get the best results with the fewest pipes.● Choose a cooler that will give a good grain bed depth for your typical batch. I recommend a depth of 4 to 12 inches.
The following four plots summarize the analysis of all the numerical models for pipe spacing, wall spacing, and depth for half-inch diameter pipes. Each plot shows the behavior of the stated quantity as a function of center-to-center pipe spacing, and as a function of grain bed depth. The relationships are nearly linear except at close pipe spacings and shallow grain bed depths.
Designing Pipe Manifolds for Continuous Sparging
Now that you know how to design a copper pipe manifold, let’s build one. A manifold can be made of either soft or rigid copper tubing. Choose the form to suit your cooler and design. In a round cooler, the best shape is a circle divided into quadrants, although an inscribed square seems to work just as well. See Figure 189 (App. E). In a rectangular cooler, the best shape is rectangular with several legs to adequately cover the floor area. When designing your manifold, keep in mind the need to provide full coverage of the grain bed while minimizing the total distance the wort has to travel to reach the drain.
In addition, it is very important to avoid channeling of the water down the sides, which will happen if you place the manifold too close to the walls. The distance of the outer manifold tubes to the cooler wall should be half of the manifold tube spacing or slightly greater. This results in water along the wall not seeking a shorter path to the drain than wort that is dead center between the tubes.
The transverse tubes in the rectangular tun should not be slotted. The longitudinal slotted tubes adequately cover the floor area, and the transverse tubes are close enough to the wall to encourage channeling. The slots should face down—any wort physically below the slots will not be collected. In a circular tun, the same guidelines apply, but if you are using an inscribed square, the transverse tubes can be slotted where they are away from the wall.
In addition, it is very important to avoid channeling of the water down the sides, which will happen if you place the manifold too close to the walls. The distance of the outer manifold tubes to the cooler wall should be half of the manifold tube spacing or slightly greater. This results in water along the wall not seeking a shorter path to the drain than wort that is dead center between the tubes.
The transverse tubes in the rectangular tun should not be slotted. The longitudinal slotted tubes adequately cover the floor area, and the transverse tubes are close enough to the wall to encourage channeling. The slots should face down—any wort physically below the slots will not be collected. In a circular tun, the same guidelines apply, but if you are using an inscribed square, the transverse tubes can be slotted where they are away from the wall.
Figure 195 – Convergence of fluid flow to a single manifold pipe running down the middle.
Large triangular areas to the sides unsparged.
Figure 196a—These pictures show the flow vectors in a lauter tun consisting of a single pipe and double pipes. The size of the arrows indicates the relative speed of the flow. Note how the flows converge to the pipes, leaving low flow areas in the corners. This same behavior has been observed when flowing food coloring dye through a grain bed in a glass aquarium.
Figure 196b—These pictures show the flow vectors in a lauter tun consisting of a single pipe and double pipes. The size of the arrows indicates the relative speed of the flow. Note how the flows converge to the pipes, leaving low flow areas in the corners. This same behavior has been observed when flowing food coloring dye through a grain bed in a glass aquarium.
Table 35 - Effect of Pipe to Pipe Spacing
Modeled on a tun that was 10 inches wide and 8 inches deep.
Table 36 - Effect of Wall Spacing
Modeled on a tun that was 10 inches wide and 8 inches deep.
Refer to Figure 201 for diagram of wall spacing.
Figure 206 - Ring efficiency by diameter.
Designing Ring Manifolds for Continuous Sparging
Ring-shaped manifolds or stainless steel braids are an elegant-looking system for round beverage coolers, but how efficient are they? It turns out that they are pretty good if we apply the balanced spacing concept. For a single ring, balanced spacing means having an equal volume inside and outside the ring. The diameter of the ring that divides the tun volume in half is expressed mathematically by the equation:
Dring = 0.707 Dtun
The following charts plot the efficiency quantities of rings and false bottoms in a Sankey keg as a function of diameter. The total diameter of a Sankey keg is 15 inches. The half-volume diameter is 10.6 inches. It is interesting to note that a single ring is more efficient than a false bottom until the false bottom diameter is at least 80% of the tun diameter. These ratios hold true for any tun diameter. If more rings were added in a balanced spacing manner, the efficiency would improve and approach that of false bottoms, just like rectangular manifolds in rectangular coolers.
Dring = 0.707 Dtun
The following charts plot the efficiency quantities of rings and false bottoms in a Sankey keg as a function of diameter. The total diameter of a Sankey keg is 15 inches. The half-volume diameter is 10.6 inches. It is interesting to note that a single ring is more efficient than a false bottom until the false bottom diameter is at least 80% of the tun diameter. These ratios hold true for any tun diameter. If more rings were added in a balanced spacing manner, the efficiency would improve and approach that of false bottoms, just like rectangular manifolds in rectangular coolers.
How to Continuous Sparge
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 37-ish points per pound per gallon for a two-row barley base malt. This means that if 1 pound of this malt is crushed and mashed in 1 gallon of water, the wort will have a specific gravity of 1.037. Most brewers would get something closer to 1.030. This difference represents an extraction efficiency of 80%, and the difference could be attributed to poor conversion in the mash, but it can also be caused by lautering inefficiency.
Our goal in the continuous sparging process is to rinse all the grain particles in the tun of all the sugar. To do this we need to focus on two things:● Keep the grain bed completely saturated with water.● Make sure that the fluid flow through the grain bed to the drain is slow and uniform.
By keeping the grain bed covered with at least an inch of water, the grain bed 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 grain bed due to loss of fluidity leads to preferential flow and poor extraction.
Continuous sparging depends on being able to rinse the sugars from the grist, and a big part of this process is diffusion. If you rinse quickly, you will end up with mostly sparge water in your boiler, because the sugar won’t have time to diffuse into the sparge water as it flows past.
Our goal in the continuous sparging process is to rinse all the grain particles in the tun of all the sugar. To do this we need to focus on two things:● Keep the grain bed completely saturated with water.● Make sure that the fluid flow through the grain bed to the drain is slow and uniform.
By keeping the grain bed covered with at least an inch of water, the grain bed 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 grain bed due to loss of fluidity leads to preferential flow and poor extraction.
Continuous sparging depends on being able to rinse the sugars from the grist, and a big part of this process is diffusion. If you rinse quickly, you will end up with mostly sparge water in your boiler, because the sugar won’t have time to diffuse into the sparge water as it flows past.
Continuous Sparging Procedure
In general, the equipment setup for continuous sparging is the same as for batch sparging. But you can make it easier on yourself by using another cooler as a hot water tank and feeding the sparge water continuously with a valve and hose. If your grain bed is shallow, you may want to direct this flow onto a coffee can lid to keep it from stirring up and clouding the wort. Rotating sparge arms and drip coils are another convenient way to deliver the sparge water to the tun. However you do it, you need to maintain an inch of free water over the grain bed to keep it fluid.
A surface layer of fine grain particles and protein, called top dough or teig, will tend to form on top of the grain bed during continuous sparging, and this layer should either be removed or broken up, so it doesn’t form an impermeable cap that will prevent the grain under it from being rinsed properly. Commercial breweries use rotating rakes to avoid this problem and prevent channeling. Their lauter tuns are typically 3 feet deep or more, and they can run the rakes within a few inches of the false bottom to ensure good extraction without losing clarity. Homebrewing lauter tuns are typically only 4 to 12 inches deep, so it is harder to stir without causing turbidity in the wort, but stirring the upper levels of the grain bed during the lauter will help extraction. Here is the general procedure:
1. Recirculate. Open the outflow valve slowly, and drain some wort into a quart pitcher. The wort will be cloudy with bits of grain. Close the valve, and gently pour the wort back into the grain bed, recirculating the wort. Repeat this procedure until the wort exiting the tun is pretty clear (like unfiltered apple cider). It will be dark amber and hazy, but not cloudy. It should only take a couple of quarts.
2. Lauter. Once the wort has cleared, begin adding sparge water, and drain the wort carefully into your boiling pot. Fill the pot slowly at first, and allow the level to cover the outlet tube. Be sure to have a long enough tube so that the wort enters below the surface and does not splash. The splashing of hot wort before the boil can cause long-term oxidation damage to the flavor of the beer.
The sparge water can be added either with a hose from a hot water tank or by pouring in a couple of quarts at a time with a pitcher. Pour it onto a coffee can lid if necessary, and be sure to maintain at least an inch of free water above the grain bed. Watch the outflow rate; you do not want to lauter too fast, as this could compact the grain bed and you would get a stuck sparge. A maximum rate of 1 quart per minute is recommended. Continue adding sparge water and draining the wort into your pot.
3. Stuck sparge? If the wort stops flowing, even with water above the grain bed, then you have a stuck sparge. There are two ways to fix it: (a) Blow back into the outlet hose to clear any obstruction; or (b) Close the valve and add more water, stirring to dilute and resuspend the mash. You will need to recirculate again. Stuck sparges are an annoyance but usually not a major problem.
4. Gauge your progress. An advantage to brewing a dark beer is that you can see the color of the wort change as you lauter. It will get a lot lighter when most of the sugars are extracted. If you lauter too fast, you will not rinse the grains effectively, and you will get poor extraction. So, watch your wort volume, runoff color, and check the runoff gravity with your hydrometer periodically as you near your boiling volume. You will want to collect about 1 to 1.5 gallons more than your batch size and boil down to your target gravity. If you oversparge, the mash pH will rise abruptly, as the runnings gravity will fall below 1.012, and tannin extraction is likely. Hopefully, you will have collected enough wort before your runnings fall below 1.012. This rise in wort pH as a function of gravity depends greatly on the mash chemistry. In a distilled water mash, the pH could be expected to rise when the gravity falls below 1.020. In water that has a calcium level between 100 and 200 ppm, the wort pH won’t rise significantly even when the runnings fall below 1.008.
A surface layer of fine grain particles and protein, called top dough or teig, will tend to form on top of the grain bed during continuous sparging, and this layer should either be removed or broken up, so it doesn’t form an impermeable cap that will prevent the grain under it from being rinsed properly. Commercial breweries use rotating rakes to avoid this problem and prevent channeling. Their lauter tuns are typically 3 feet deep or more, and they can run the rakes within a few inches of the false bottom to ensure good extraction without losing clarity. Homebrewing lauter tuns are typically only 4 to 12 inches deep, so it is harder to stir without causing turbidity in the wort, but stirring the upper levels of the grain bed during the lauter will help extraction. Here is the general procedure:
1. Recirculate. Open the outflow valve slowly, and drain some wort into a quart pitcher. The wort will be cloudy with bits of grain. Close the valve, and gently pour the wort back into the grain bed, recirculating the wort. Repeat this procedure until the wort exiting the tun is pretty clear (like unfiltered apple cider). It will be dark amber and hazy, but not cloudy. It should only take a couple of quarts.
2. Lauter. Once the wort has cleared, begin adding sparge water, and drain the wort carefully into your boiling pot. Fill the pot slowly at first, and allow the level to cover the outlet tube. Be sure to have a long enough tube so that the wort enters below the surface and does not splash. The splashing of hot wort before the boil can cause long-term oxidation damage to the flavor of the beer.
The sparge water can be added either with a hose from a hot water tank or by pouring in a couple of quarts at a time with a pitcher. Pour it onto a coffee can lid if necessary, and be sure to maintain at least an inch of free water above the grain bed. Watch the outflow rate; you do not want to lauter too fast, as this could compact the grain bed and you would get a stuck sparge. A maximum rate of 1 quart per minute is recommended. Continue adding sparge water and draining the wort into your pot.
3. Stuck sparge? If the wort stops flowing, even with water above the grain bed, then you have a stuck sparge. There are two ways to fix it: (a) Blow back into the outlet hose to clear any obstruction; or (b) Close the valve and add more water, stirring to dilute and resuspend the mash. You will need to recirculate again. Stuck sparges are an annoyance but usually not a major problem.
4. Gauge your progress. An advantage to brewing a dark beer is that you can see the color of the wort change as you lauter. It will get a lot lighter when most of the sugars are extracted. If you lauter too fast, you will not rinse the grains effectively, and you will get poor extraction. So, watch your wort volume, runoff color, and check the runoff gravity with your hydrometer periodically as you near your boiling volume. You will want to collect about 1 to 1.5 gallons more than your batch size and boil down to your target gravity. If you oversparge, the mash pH will rise abruptly, as the runnings gravity will fall below 1.012, and tannin extraction is likely. Hopefully, you will have collected enough wort before your runnings fall below 1.012. This rise in wort pH as a function of gravity depends greatly on the mash chemistry. In a distilled water mash, the pH could be expected to rise when the gravity falls below 1.020. In water that has a calcium level between 100 and 200 ppm, the wort pH won’t rise significantly even when the runnings fall below 1.008.