Wort absorption for BIAB

[kshuler]

Hi guys,

Completed an experiment on my last brew about wort absorption. I do BIAB brewing and am almost always getting exactly 81% lautering efficiency. I think I know why people can get such good yields, and it is mainly to do with extracting more wort from the grain than one would predict by traditional three vessel calculations. In an effort to quantify it, I ran a little experiment.

My last brew used 15.57 lbs of grain in a 7 gallon batch. After mashing and squeezing the bag (not particularly gently), I ended up with a bag of wet grain weighing 16.25 lbs. I took a pound of this, spread it out on a cookie sheet and weighed it after 8 hours at 200 degrees, and the final weight was 5.375 oz.

This means the wet spent grain even after squeezing is 66.4% water and only 33.6% grain (and residual sugar). That means the 15.57 lbs of original grain only absorbed about 1.3 gallons of wort, making total grain absorption only 0.083 gallons per pound, or in other words 0.333 quarts of wort per pound of grain.

Compared to the standard value I have read of around 1.25 quarts per pound for traditional 3 vessel brewing, I think this is the probably reason that people's efficiencies for BIAB are somewhat higher than skeptics have expected. My pre boil volume was 9.09 gallons, so the theoretical maximum efficiency given the dryness of the grain would be:

(preboil volume)-(absorbed grain)
----------------------------------------
(preboil volume)

or (9.09-1.3)/9.09= 85.7% efficiency with 100% starch conversion. This fits nicely with my calculated conversion efficiency of 81%, for a theoretical 94.5% conversion efficiency.

Gotta love science!

Bottom line, BIAB grain absorption with squeezing should not be 1.25 quarts per pound of grain, but closer to 0.333 quarts per pound of grain.

Klaus

 

[kmk1012]

Your math passed me up but, I do full volume mashes/boils starting with 9.0gal. I mash for 75min, boil for 60 min, no sparge (I drain grain with a bucket in a bucket system) and always end up with 5.75 to 6.25 gallons of wort. This is usually with 9-13lbs of grain. My squishy math skills put your calculations on par with my experiences for the past 16 beers.

 

[Mysticmead]

taking the grain weight and multiplying by .08 works for me.. if you want to add a buffer make it 0.10. helps me determine the amount of water needed for a full volume BIAB in the formula weight in Lbs x .10 = absorption
final volume + absorption + trub loss + boil off = total water needed.

I guess using .10 adds enough extra water to cover loss to cooling which should be roughly 4%

 

[ultravista]

Good stuff kshuler.

While I have not made the full leap into BIAB, I do MIAB. When mashing in a bag I had great efficiency and little or no loss to dead space. The mash was clean and the tun drained completely. And when HIAB (hoping in a bag), there is little or no trub / detritus in the boil kettle either.

Both contribute to efficiency.

 

[studmonk3y]

0.333 quarts of wort per pound of grain.

Klaus

I get about this value as well. Sometimes even as low as 0.25 quarts/lb.

 

[Buna_Bere]

The number I've usually seen for grain absobrtion is 0.125 gallons per pound, or 0.50 quarts per pound. I've measured 0.10 gallons per pound, and 0.09 gallons per pound with biab with a 10 minute drip in a strainer and no squeeze.

Bob