Sparging is simply rinsing the spent grain. When you drain the wort from the grain in the mash tun, some of the sugary wort sticks to the grain grits, and you don't get all of the sugar available with a simple wort run-off. You can recover some of the sugar adsorbed by the grain by using less water for mashing, and using the withheld water to rinse the grain. You rinse the grain with fresh water, not drained wort, for the same reason you don't rinse dishes after washing by putting them back in the soapy water.
The easiest way to brew is just use all of the water you need to reach your pre-boil volume for mashing. This is known as full volume, or no-sparge mashing. The volume of water you need to mash with (your strike volume) is equal to your desired pre-boil volume plus the volume you expect the grain to absorb. The typical apparent grain absorption rate for a traditional MLT is about 0.12 gal/lb of grain. That means if you mash 10 lbs of grain you can expect to collect 1.2 gal less wort than your strike water volume. So, if you want 6.5 gal of wort pre-boil, you would mash your 10 lb of grain with 7.7 gal of strike water.
Now it turns out that with 10 lb of grain and 7.7 gal of strike water, you will actually create 8.28 gal of wort in the mash. The extra 0.58 gal of wort volume is due to the volume of sugar (and other components) dissolved in the wort. When you drain the mash, you will collect 6.5 gal of wort, which means the grain is still holding 1.78 gal of wort. The mash created 7.68 lb of extract (sugar and other dissolved material), the run-off in your BK contains 6.03 lb of that extract, and 1.65 lb of your extract is still in the spent grains. Your mash efficiency (assuming you got 100% conversion) is then 6.03 / 7.68 = 78.5%
Now, let's see what happens if we batch sparge instead of doing a full volume mash. In this case we want to collect 3.25 gal of wort from the initial mash run-off, and 3.25 gal of wort from the sparge run-off. In this case our strike volume is 3.25 + 1.2 = 4.45 gal. We will still create 7.68 lb of extract in the mash, and our initial run-off of 3.25 gal will contain 4.96 lb and the grain will retain 2.72 lb.
We now add 3.25 gal of fresh water to the spent grains, and mix thoroughly, and drain 3.25 gal of sparged wort. The sparged wort will contain 1.76 lb of the 2.72 lb of extract left in the grain after our initial run-off. There will only be 0.96 lb of extract left in the grain after draining the sparged wort. This compares to 1.65 lb of extract left in the grain from the no-sparge process. The total extract collected in the two run-offs is 4.96 + 1.76 = 6.72 lb vs. the 6.03 lb in the no-sparge case. Our mash efficiency with sparging is 6.72 / 7.68 = 87.5% vs. 78.5% for the no-sparge case.
So, using the same amount of brewing water, and getting the same pre-boil volume, we have increased our mash efficiency by 9 percentage points by doing a single batch sparge step.
Here is the basic mash and sparge process for batch sparging.
- Heat strike water to mash-in temperature (slightly hotter than desired mash temp) and mix in the crushed grain. Strike water volume is 1/2 pre-boil volume + expected grain absorption volume
- Hold mash at target temperature for desired mash time (usually about an hour.)
- Stir mash well, and drain all the wort into your boil kettle (drain speed doesn't matter.)
- Add sparge water to spent grain in mash tun, and stir aggressively for about 5 minutes. Sparge water volume is 1/2 pre-boil volume.
- Drain all sparged wort into the BK with the initial wort.
- Mix well (again about 5 minutes) and take your pre-boil volume and SG measurements.
- Boil wort.
Note that it is not actually necessary to heat the sparge water, although doing so will shorten the time it takes to get your wort to boiling. So, if you don't have a second kettle to heat sparge water, don't worry about it.
You can also do multiple batch sparges by repeating steps 4 and 5 above. For two batch sparges, the water volume calculations above use 1/3 instead of 1/2, and for three batch sparges use 1/4. Each additional sparge step will increase you lauter (and thus mash efficiency) somewhat, but you get less benefit from each additional step as you do more steps (diminishing returns.)
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