I am going to brew a high gravity Imperial Stout, probably around 10%-11%, with a 24 pound grain bill in a 15 gal kettle. Will I be able to mash all the sugars out of the grain with a conventional mash or should I consider using a double mash or a different approach with such a large grain bill?
High Gravity Stout using BIAB
- Thread starter Preeway
- Start date
Help Support Homebrew Talk:
Assuming a 1 gal boil-off and 0.08 gal/lb grain absorption rate, your strike water volume will be 8.42 gal, and your mash volume will be just under 10.5 gal. If you have a higher boil-off or higher grain absorption, you will need more strike volume to compensate, and your mash volume will increase accordingly. Higher grain absorption will decrease your lauter and mash efficiencies.
If you get 100% conversion, your OG should come in around 1.100 - 1.102. Your mash efficiency would be around 65 - 66% (due to the big grain bill efficiency penalty.) If your conversion efficiency is lower, your mash efficiency and OG will be proportionately lower.
Brew on
If you get 100% conversion, your OG should come in around 1.100 - 1.102. Your mash efficiency would be around 65 - 66% (due to the big grain bill efficiency penalty.) If your conversion efficiency is lower, your mash efficiency and OG will be proportionately lower.
Brew on
Rush
Well-Known Member
I have been doing BIAB for my last 6-7 batches and have had a pretty consistent 75% efficiency. This efficiency was doing full volume mash's in a 10G kettle with 10-15LBs of grain.
Two days ago I attempted an imperial stout, which was the highest gravity(1.100)I was trying to achieve since I started BIAB. Mash was thick with 20LBS of grain in 8G of water.
Mash efficiency dropped hard, down to 60% so I'm lucky I had enough dry malt extract to boost the OG back up once the boil was done.
Next time I'm going to use 60-65% efficiency for the calculator, and possibly add a sparge step.
Doing a high gravity beer is doable, but just plan accordingly and adjust your mash efficiency down a decent amount.
Two days ago I attempted an imperial stout, which was the highest gravity(1.100)I was trying to achieve since I started BIAB. Mash was thick with 20LBS of grain in 8G of water.
Mash efficiency dropped hard, down to 60% so I'm lucky I had enough dry malt extract to boost the OG back up once the boil was done.
Next time I'm going to use 60-65% efficiency for the calculator, and possibly add a sparge step.
Doing a high gravity beer is doable, but just plan accordingly and adjust your mash efficiency down a decent amount.
![Craft A Brew - Safale S-04 Dry Yeast - Fermentis - English Ale Dry Yeast - For English and American Ales and Hard Apple Ciders - Ingredients for Home Brewing - Beer Making Supplies - [1 Pack]](https://m.media-amazon.com/images/I/41fVGNh6JfL._SL500_.jpg)
Rush
Well-Known Member
I lost 15% in efficiency going from 12-15LB's of grain for a normal brew to 20LB for an RIS.
The drop in lauter efficiency with larger grain bills is totally predictable. Mash efficiency (which equals conversion efficiency times lauter efficiency) is not as predictable, since a thicker mash will convert slower than a thinner mash (ref.), and thus might have lower conversion efficiency if mash time is not increased to compensate for slower conversion. Conversion efficiency is not predictable, but it is measurable using the method here. So, with a large grain bill you may want to consider increasing your mash time, and monitoring the SG of the wort in the mash to determine when the mash is complete. SG monitoring is more reliable than an iodine test, which can give misleading results.
It turns out that for no-sparge and batch sparge processes, lauter efficiency is a function of grain bill weight divided by the pre-boil volume. By using the ratio of grain bill weight to pre-boil volume, lauter efficiency becomes independent of batch size (for a specific process and grain absorption rate.) The chart below shows how lauter efficiency varies with the grain to pre-boil ratio for both no-sparge and single, equal run-off volumes, batch sparge for a variety of different grain absorption rates. Typical MLT processes have a grain absorption rate of about 0.12 gal/lb. BIAB grain absorption rates can vary from about 0.05 gal/lb for very aggressive squeezing to about 0.10 gal/lb for just gravity draining the bag (drain time will affect this.)
A typical 5.5 gal batch with 6.5 gal pre-boil volume and a 10 lb grain bill has a grain to pre-boil ratio of 1.54, and falls on the left side of the chart. That same batch and pre-boil size with 24 lb of grain has a ratio of 3.69, and falls on the right side of the chart. For larger grain bills, going with a higher pre-boil volume and higher boil off can give you some improvement in efficiency. For example, with 24 lbs and 7.5 gal pre-boil, the ratio becomes 3.2 instead ~3.7, which translates to about 3 - 3.5 percentage points improvement in lauter efficiency.
Brew on
