The most effective way to sparge when doing BIAB is to dunk sparge using about 60% of your total water for mashing, and the remaining 40% for sparging. Since grain absorption losses only affect the initial run-off volume (grain is already saturated during the sparge, so no additional absorption losses occur), this will get you close to equal volumes of wort from the initial mash and the sparge, which is the optimal condition for lauter efficiency.
The grain absorption rate has a large effect on lauter efficiency for both no-sparge and batch sparge, with lower absorption rates leading to higher efficiency. You can decrease your grain absorption rate by draining for a longer time, or squeezing the bag.
A pour over sparge is kind of like a fly sparge, but you don't have control over the drain rate, so can't do much to mitigate channeling in the grain mass (which reduces the effectiveness of the sparge), nor allow more contact time with the sparge water to allow sugar to diffuse into the sparge water (the sparge water will not pick up as much sugar on the way thru as it could under optimal conditions.) Pour over sparges are less controllable than batch/dunk sparges, so will have a higher variability batch to batch, and once you have acceptable efficiency, consistency is more important than getting another 1% of lauter efficiency.
Here's how to conduct a dunk (batch) sparge:
- At the end of the mash, open the bag and stir the mash aggressively to homogenize the wort.
- Lift the bag out of the wort, and allow to drain well. The longer you drain, the lower your grain absorption and the higher your efficiency will be.
- (Optional) Squeeze the bag. Doing so will reduce your grain absorption even further than the initial drain alone, again increasing lauter efficiency.
- Lower the grain bag into a bucket containing your sparge water (can be hot or cold, doesn't matter for lauter efficiency), open the bag, and stir aggressively to make sure the sugar is rinsed off/out of the grits to the maximum extent possible. Optionally, you can put the grain bag in the bucket first, and then add the sparge water.
- Lift the bag out of the sparged wort, and allow to drain well. The longer you drain, the lower your grain absorption and the higher your efficiency will be.
- (Optional) Squeeze the bag. Doing so will reduce your grain absorption even further than the drain alone, again increasing lauter efficiency.
- Proceed to boil. It's fine to start heating the initial run-off wort while you are sparging.
If you only want to squeeze once, you should do it prior to the sparge, as this will have a larger positive effect on your lauter efficiency than just squeezing after the sparge.
Cold sparge vs. hot sparge: A hot sparge will reduce the time required to bring the wort to a boil after the sparge is complete, but will not reduce the total energy required for heating water & wort.
If your conversion was not complete at the time of your initial wort draining,
AND you have not done a mash-out, a hot sparge
may allow some additional conversion to occur during the sparge, which would improve your conversion efficiency a little.
Here's one of my favorite charts that shows how grain bill size, sparge process, and grain absorption rate affect lauter efficiency:
View attachment 877568
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