Purpose: To determine the volume of water additions needed for batch sparging
Results: *** Waiting for results ***
Batch sparging rinses sugars from the mash by introducing the sparge water in large volumes. This method is popular with modern homebrewers because it is simple and fast. The standard batch sparge approach is to aim for two equal volumes of runnings from the mash tun. The basic procedure is described by Denny Conn in a now classic article.
Conn's formula for the first runnings is:
(targetVolume/numberRuns) - ((strikeWater + stepWater) - (grainWeight * retentionRatio))
In brief, the left side of the formula determines equally sized run volumes. The right side of the formula reduces the first sparge water addition based on strike water and step water that are already in the mash while adjusting for water lost due to retention by the grain bed. The second or third sparge water additions are typically half or one-third of the target volume. The default values in this calculator produce the same results as Denny Conn's example.
The standard batch sparge goal of obtaining equally sized runnings will be upset if the mash is either very large or really thin. The calculator adapts to these situations by making the first sparge water addition zero. The sparge water needed for the second and possibly third runnings is then adjusted downward to compensate for the excess volume from the first running. This adjustment attempts to keep the spirit of equally sized runnings.
One possibility is that you might fall short of your target volume. This could occur if your grain bed is retaining more water than .1 gallon per pound, which is the retention amount suggested by Conn. The solution, for the next brew, is to try adjusting the water retention factor up just a bit, such as .125.
The first homebrew batch sparge calculations from Ken Schwartz and others had extra calculations for a scaling factor. The reason was that homebrewers in the late 1990s were using recipes developed based on continuous sparge efficencies such as 85% or 90% efficiency. These highly efficient grain bills had to be adjusted upward with more grain -- the scale-up factor -- to compensate for the lower efficiencies of batch sparging. In contrast to the 1990s, most current recipes start with lower assumptions for mash efficiency, such as 70% to 80%. Recipes based on these lower efficencies should not need to be scaled up.
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