Full volume high gravity biab limits?

[brewprint]

I did a 5.5 gallon full volume batch the other day and I was shooting for an SG of 1.074 which would've been 75% but I only ended up with 1.068.

I thought that someone said that a limitation of BIAB is doing higher gravity with full volume. That some kind of sparge would be necessary to achieve a higher efficiency.

Currently I'd like to try this again but with a smaller 3.5 gallon batch. Am I going to run into the same issue?

 

[BigDog007]

I made a Pliny the Elder clone last week which calls for 5.5 gallons in the fermenter. My OG was 1.081, I do BIAB using RIMS.

Some of the things I do:

-Double crush the grains either at the LHBS or get a mill
-Stir the mash several times during the process
-Do a partial sparge on the grain bag, I tried this once and haven't had to do it since
-Setup something so you can squeeze the heck out of the grain bag when you pull it

Like I said I did a full RIMS build so the recirculation during the mash seems to do a good job but I also double crush, stir it a few times and squeeze the heck out of the bag at the end.

The only problem I'm having now is sometimes I overshoot my pre-boil volume so in the future I'm only going to squeeze what I need for the boil minus my expected boil-off and shrink.

Good luck!

 

[brewprint]

I stir the mash pretty well but only do a 60 minute and only stir every 20 minutes. Maybe if I got another stir in there and did it every 15 for the higher gravity that would work?

My grains are triple crushed.

I do squeeze the bag pretty well but I just use cutting board to do it. I'm sure there's some water in there yet. I also let the bag drain until the boil is achieved.

I'm going to try again but do a 3.5 gallon batch. I may shoot for the 1.080 OG. I don't really need 2 cases of beer of that high of alcohol beer anyway

 

[BigDog007]

I'm not sure what your crush looks like but if it's like flour that could be an issue. Might consider with going only twice or adjusting the gap.

I crushed last week with my mill and had it set to fine so I only ran it once and still got really good efficiency ~75%

 

[brewprint]

Too much of a crush is bad?

 

[TexasWine]

Too much of a crush is bad?

As your crush gets closer to being flour like it is easier to form dough balls, so you just have to be more attentive to that. Other than that, I can't think of any draw backs to a finer crush with BIAB.

 

[Chadwick]

I achieve very high O.G. brews with BIAB through these techniques.

1) Very well milled grains in my mill. I shoot for something that looks like a really course corn meal.

2) Stepped mash. I'll dough in at around 120F and slowly bring the temp up to my target and then hold that for an extended period of time. 90 minutes usually, sometimes a bit longer.

3) Once the mash is completed I'll collect as much of the wort that I can get out of the kettle and store it in another container. Then I'll pour sparge water back into the mash with the spent grains. Stir it like it owes me money and then pull the bag out and let it drain until it's finished.

4) I'll pour the wort I collected earlier back into the mash tun which now my brew kettle and turn the heat on for the boil.

My starting boil volume is usually around 8.5 gallons when I'm doing big brews. As a result I find I'm sometimes boiling for an hour before I even do my first hop addition, but this process works for me. I have no trouble brewing high gravity ales using a BIAB method. I've gone as high as 1.100 OG. All of this with a 10 gallon kettle.

 

[Pezzonovante11]

First of all, reaching an OG of 1.068 on a recipe of 1.074 is actually closer to target than you think, so you did a decent job.

The problem with BIAB and high gravity results from grain absorption.
You can mill finely to improve your extraction, but even if you could extract 100% it won't solve the problem.

Since you are necessarily decreasing the water:grain ratio with high gravity brews, the grain absorption as a percentage of the mash water is going to rise, and so the gravity points lost to grain absorption will rise with it.

You basically have three options to improve efficiency:

1. Decrease grain absorption by wringing out/pressing the grains in some way
2. Sparge
3. Decrease your ratio of grain absorption by increasing your water:grain ratio with more mash water and increase your boil-off to compensate.

Or use some combo of the above three.

Example:
Let's say you use 12# of grain, and mash with 8 gallons of water.
Assume grain absorption is 0.12gallons/pound of grain, 100% mash conversion, no dead space, and boiling off 1 gallon in 60 minutes:

Grain absorption is 1.44 gallons, leaving you 8-1.44=6.56gallons of pre-boil wort. You would boil-off 1 gallon leaving 5.56 gallons to fermenter with an OG of 1.064 and a to-fermenter efficiency of 82%

Now you do the same brew but you increase your mash water to 8.5 gallons. Lets also squeeze the heck out of your bag, decreasing your grain absorption to 0.06gal/pound. Lets say you also boil for 90 minutes and more vigorously so your boil-off rate increases to 1.5 gallons per hour. The same brew would look like this:

Grain absorption is 0.06*12=0.72gal, leaving you 8.5-.72=7.78gal pre-boil.
You would boil-off 2.25gal, leaving you with 5.53gallons into fermenter with an OG of 1.072 and an efficiency of 92%

I've neglected a lot of details like hop absorption, cooling loss, and deadspace but you get the idea. You just increased your efficiency by 10% and you didn't even have to sparge.

To answer your question, on a smaller batch size since you will boil off the same hourly rate as you would on a big batch, so the proportion of boil-off to mash water will increase and you should get a somewhat higher efficiency.

 

[TexasWine]

I've gone as high as 1.200 OG. All of this with a 10 gallon kettle.

Whoa! What was your preboil gravity? And your FG?

 

[douglasbarbin]

Not sure if this has been mentioned yet, but you can achieve a higher gravity with a longer boil.

 

[Chadwick]

Whoa! What was your preboil gravity? And your FG?

lol, you got me. I've gotten to 1.100 without adding sugars to the wort. I'll go edit that now.

 

[TexasWine]

lol, you got me. I've gotten to 1.100 without adding sugars to the wort. I'll go edit that now.

Whew! I was about to ask what magical powers you employed to get to such a number.

 

[brewprint]

First of all, reaching an OG of 1.068 on a recipe of 1.074 is actually closer to target than you think, so you did a decent job.

The problem with BIAB and high gravity results from grain absorption.
You can mill finely to improve your extraction, but even if you could extract 100% it won't solve the problem.

Since you are necessarily decreasing the water:grain ratio with high gravity brews, the grain absorption as a percentage of the mash water is going to rise, and so the gravity points lost to grain absorption will rise with it.

You basically have three options to improve efficiency:

1. Decrease grain absorption by wringing out/pressing the grains in some way
2. Sparge
3. Decrease your ratio of grain absorption by increasing your water:grain ratio with more mash water and increase your boil-off to compensate.

Or use some combo of the above three.

Example:
Let's say you use 12# of grain, and mash with 8 gallons of water.
Assume grain absorption is 0.12gallons/pound of grain, 100% mash conversion, no dead space, and boiling off 1 gallon in 60 minutes:

Grain absorption is 1.44 gallons, leaving you 8-1.44=6.56gallons of pre-boil wort. You would boil-off 1 gallon leaving 5.56 gallons to fermenter with an OG of 1.064 and a to-fermenter efficiency of 82%

Now you do the same brew but you increase your mash water to 8.5 gallons. Lets also squeeze the heck out of your bag, decreasing your grain absorption to 0.06gal/pound. Lets say you also boil for 90 minutes and more vigorously so your boil-off rate increases to 1.5 gallons per hour. The same brew would look like this:

Grain absorption is 0.06*12=0.72gal, leaving you 8.5-.72=7.78gal pre-boil.
You would boil-off 2.25gal, leaving you with 5.53gallons into fermenter with an OG of 1.072 and an efficiency of 92%

I've neglected a lot of details like hop absorption, cooling loss, and deadspace but you get the idea. You just increased your efficiency by 10% and you didn't even have to sparge.

To answer your question, on a smaller batch size since you will boil off the same hourly rate as you would on a big batch, so the proportion of boil-off to mash water will increase and you should get a somewhat higher efficiency.

Thanks for this post!

My plan is on my next batch I'm going to do a 3.5 gallon batch. I'm going to increase my water volume size by at least 1/2 gallon and increase the boil time by 30 minutes to compensate. Shooting for an OG of 1.094.

 

[HarboBrew]

Since there is no worries about a stuck sparge in BIAB there is no real reason not to fine crush your grains. Just throw in whirlfloc/Irish moss to help precipitate the extra suspended sediment post boil.