 |
|
|
|
 |
 |
 |
 |
 |
 |
 |
 |
 |
|
 |
South Bay, Los Angeles County, California |
 |
|
In August, the Dregs included a report on the No Sparge Brewing session at NHC 2001. That article included an example recipe for sparge vs. no sparge brewing, but did not include the equations used in the procedure. At that time, I was still a little confused at the abundance of equations given at the session for calculating the no sparge details. I thought, though, that it shouldn't be as complicated as it seemed. After spending way too much time thinking about this, I think I can clarify the no sparge procedure. We need to know two empirical values for the no sparge process: the amount of liquid retained per pound of grain at the end of the mash, and the volume of the grains themselves. Let's assume that every pound of grain retains 0.5 quart of water. This is the value given by the speaker during the NHC session. For the volume of the grains themselves, I know I can just about fit 26.5 pounds of grain with 1 quart of water per pound in a 10-gallon Gott cooler, and therefore one pound of grain in one quart of water has a volume of 1.5 quarts. Conceptually, the no sparge procedure is very simple: At the end of a normal mash, a large infusion of hot water is added to the grains, and the resulting sweet liquid drained into the kettle. Since we don't rinse the grains, they retain liquid with the same sugar concentration as what was just drained from the lauter tun. As the gravity of the mash liquid decreases, the total amount of sugars retained by the grains also decreases. But as we decrease the mash liquid gravity by increasing the final infusion volume, we also increase the wort volume drained into the kettle. How do we size the amount of grain and the final infusion volume? The desired target for no sparge brewing is to dilute the mash liquid to the pre-boil gravity while simultaneously sizing the final mash volume so that the total wort drained from the lauter tun equals the desired pre-boil volume. We need to determine the amount grain and find the total water necessary to meet these two goals. We know that we want to make a certain volume of beer at some OG. We can express this beer strength in gravity units (GU), which is the product of the volume of the beer in gallons and the last two digits in the original gravity reading (e.g., 6 gallons of 1.050 OG wort has 300 GU). We also know the desired volume of the boil since we know our evaporation loss during the boil. Using the beer strength in GU and the pre-boil volume, we can use Figure 1 to find the amount of grain required for the no sparge process. Each curve in this figure is for a constant pre-boil volume, and gives the GU extracted from a given amount of grain.
For a given boil volume, as we increase the amount of grain we increase the total gravity units present in the mash run off. Eventually, there is an amount of grain where the mash liquid without the final infusion is equal to our boil volume. These points occur off the scale in Figure 1. For a given amount of grain, as we increase the boil volume we increase the GU present in the run off since we are diluting the mash and therefore decreasing the sugars left in the grains. However, the volume of the runoff increases much faster than the sugars present, and the OG of the runoff is less at the higher boil volumes. If we had plotted OG versus pounds of grain, the curves would have been in the reverse order on the figure, with the 5-gallon volume boil at the top, and the 14-gallon volume boil at the bottom. Each curve on the figure stops on the left at the point where the amount of grain results in a runoff gravity of 1.035-quite low compared to &quop;normal" beers. Figure 1 ignores any constraints on total mash volume. According to the figure, using 30 pounds of grain and a 14-gallon boil yields approximately 700 GU, which will give a wort gravity of 1.050-a standard beer. However, the total mash volume for this batch is 21.5 gallons, which will exceed the mash tun capacity of most homebrewers. We need to examine how the no sparge method changes if we constrain the total volume of the mash. If we are limited by the size of the total mash volume, we will start the no sparge process with some amount of grain, mash normally, and then add a final infusion of hot liquor that completely fills the lauter tun. We then drain as much liquid as possible into the kettle, and dilute the run off to the desired pre-boil gravity. The solid lines in Figure 2 show the GU extracted from a specified amount of grain for six fixed lauter tun sizes.
As the amount of grain increases, the total amount of liquid in the lauter tun decreases, which decreases the amount of sweet wort drained into the kettle. Eventually, we reach the point where the mash completely fills the lauter tun without leaving room for a final infusion. In Figure 2, the curves end on the right-hand side when they reach this limit. As we decrease the amount of grain the gravity of the runoff decreases, and the curves stop on the left at the point where the gravity reaches 1.035. Note that for a fixed lauter tun size there is an optimal amount of grain that yields the largest extract in terms of GU for that size equipment. If we completely fill the lauter tun with just the normal mash, there isn't any room for a final infusion. That leaves the spent grains soaked in wort with a very high specific gravity. If we cut down on the grain for the mash, we leave room for a final infusion, which dilutes the concentration of sugars wasted in the spent grains. But as we reduce the amount of grains, we are reducing the total amount of sugars present. The maximum occurs at the best balance between these two competing factors. Most homebrewers will be constrained by both the boil volume and the total mash volume in the lauter tun. In this case, we take Figures 1 and 2 together, and operate on whichever curve is most restrictive, which is the curve that results in the least GU for a specified amount of grain. The dashed line in Figure 2 is the 7.5-gallon boil volume from Figure 1. If we have a 15-gallon lauter tun and want a boil volume of 7.5 gallons, we operate on the dashed line in Figure 2 up to the 30-pound grain level, and then move onto the solid line as the grains increase to the limit of the lauter tun. For this example, using 20 pounds of grain will yield an extraction just less than 500 GU (instead of about 520 GU without the mash volume limit), which will produce a pre-boil wort around 1.067. If we stare at the graphs a while, and think about using the no sparge process in the brew house, we come to two conclusions: Conclusion 1: The spent grain in no sparge brewing retains liquid with a gravity equal to or greater than that of the beginning of the boil. If we assume we are not making a small beer from the second runnings, no sparge brewing is best suited to lower gravity beers, since our system efficiency drops as we increase the desired OG of the beer. Conclusion 2: No sparge brewing requires a lauter tun that has a volume approximately 30-40% larger than that of the wort at the beginning of the boil. This translates into a lauter tun size that approaches double that of our nominal batch size, making it difficult to produce 10 gallons of standard strength beer from a system that uses a single half-barrel keg for the lauter tun. Lauter tuns in the 10 to 15-gallon range, though, should work well for making 5 to 7 gallons of beer. If you have the equipment necessary to hold a very large mash, I encourage you to give no sparge brewing a try. Bring the result to an SBC meeting for some informal discussion of the method's merits.
|
