BIAB water displacement?

Tomorrow I am going to brew my first all grain using the BIAB method. I have an 8.5 gallon kettle and 20 lbs of grains total. I am curious how I would calculate water displacement?

I think I can mash with 6 gallons of water and still have 2.5 gallons of volume available for water displacement. My other option would be to mash with 4 gallons of water and sparge with 2.5 gallons of water.

What do you guys think? I don't really want to sacrifice much efficiency in either methods.

Have you seen this mash calculator? http://www.rackers.org/calcs.shtml (Scroll down a bit to "can I mash it")

It will tell you how much grain and water fit in a vessel. In this case, 20 pounds of grain and 1.25 quarts of water per pound of grain (6.26 gallons of water) will take up 7.85 gallons of space.

Generally agreed figure seems to be equivalent to around 0.36qt (volume) per pound (weight) of grist. Other figures run around "Uncrushed malted barley is about .75L/# dry. Malted wheat is about .65L/# dry."

http://www.homebrewersassociation.org/forum/index.php?topic=8568.0

Yooper said:

Have you seen this mash calculator? http://www.rackers.org/calcs.shtml (Scroll down a bit to "can I mash it")

It will tell you how much grain and water fit in a vessel. In this case, 20 pounds of grain and 1.25 quarts of water per pound of grain (6.26 gallons of water) will take up 7.85 gallons of space.

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Great this was the exact thing I was looking for. All the other calculators were 404. So I would be pushing it. 6 gallons seems reasonable.

Another question? Is it best to sparge or top of a carboy to meet 5 gallons? Could someone explain how mash thickness is calculated?

Tipharet said:

Great this was the exact thing I was looking for. All the other calculators were 404. So I would be pushing it. 6 gallons seems reasonable.

Another question? Is it best to sparge or top of a carboy to meet 5 gallons?

Click to expand...

Sparging is the "best" way, because if you top off you'll dilute your wort. It's ok to do that if your OG is way high but otherwise, I'd sparge to my boil volume if it at all possible.

The best thing about cutting your water back and adding in the fermenter is you can nail your OG every time!