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Old 09-21-2009, 04:21 PM   #1
bakins
 
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After seeing various discussions on BIAB, I decided to attempt to calculate the maximum efficiency possible for BIAB ( brew in a bag).

I used the info I gained from http://braukaiser.com/wiki/index.php...use_Efficiency

I had a conversation with Kai and he said my numbers looked reasonable. Any errors, however, are my fault, not his.

All water measurements are at room temperature. (If not you have to account for expansion).

Lets assume a basic 10 lb grain bill and that the grain has an 80% extract potential (pretty normal). Assume we mash in with 8 gallons of water. Now the math is much more straight forward with metric numbers, so I'll convert.

10lb = 4.5 kg
8 gallons = 30.24 L

Our maximum pre-boil gravity, since we are not sparging, assuming 100% conversion efficiency (which is doable):

4.5 * 0.8 * 100 / (4.5 * 0.8 + 30.24) = 10.64 Plato or about 1.043 SG

Assuming, the "normal" grain absorption of .125 gallons/pound (1.05 L/kg), we should collect 6.75 gallons (25.5 L).

So, our efficiency "into the kettle" is:

100 * 25.5 * 1.043 * (10.64/100) / (4.5 * 0.8) = 78%

(Note: depending on how you round, the numbers fluctuates. I did this in a spread sheet and didn't copy all the decimals to this post).

One of the claims of BIAB is lower grain absorption rate (because the bag can "squeeze" a little more wort from the grain). So, just lowering it to .1 gallon/pound, we should collect 7 gallons (26.5L). So our efficiency would be:

100 * 26.5 * 1.043 * (10.64/100) / (4.5 * 0.8) = 81%


I'm sure this is full of errors, but wanted to get a discussion going. Please correct me. I just know that I don't get the horrible efficiencies that people say I should when I BIAB.

Reason: Added bold

 
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Old 09-21-2009, 07:28 PM   #2
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Why would you get horrible efficiency with BIAB? I usually get around 70-75%...not the best in the world, but I'm also not going nuts with my sparge. If I take my time and do a proper sparge, I can easily get 75-80%. Sometimes I really half-ass and get 65% or so, but that's only when it's planned.
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Old 09-21-2009, 07:35 PM   #3
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I think if you're using a BIAB similar to this method there should be no sparge. A mashout however will greatly increase efficiency! I usually am able to get 75+% using only one pot and a bag (and some heat). Just make sure that your bag is not touching the bottom of the pot when the flame is on, or hanging over the edge for that matter.

 
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Old 09-21-2009, 07:39 PM   #4
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Yeah, the assumption is no sparge. It's not like you can't do a dunk-sparge in a secondary vessel and it has the advantage of not requiring that large of a kettle because the two worts are combined after you remove the grain bag.
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Old 09-21-2009, 08:06 PM   #5
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Yes, I'm referring to the "Aussie" Brew-in-a-bag method - no-sparge.

I just keep seeing on boards (this one included) about how you can never get above x% (where x is usually 60 or so) using no-sparge BIAB. I generally get 78%, pretty much like clockwork when I BIAB *.

And, theoretically at least, a mash-out is not needed. However, I do generally do one.

*on my last BIAB, i got 83%. I actually rechecked my numbers because that sounded high. It's possible looking at the math. I've started doughing in at 135, raise to 150, then 158, then 170 using my RIMS. the 135 helps with doughballs, probably not needed, but it's no trouble.

 
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Old 09-21-2009, 08:16 PM   #6
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That's certainly the math under ideal situations. You have to have a fine crush and convert every bit of starch. After that, it's easy because there's absolutely no dead space.
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Old 09-21-2009, 08:27 PM   #7
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Quote:
Originally Posted by Bobby_M View Post
That's certainly the math under ideal situations. You have to have a fine crush and convert every bit of starch. After that, it's easy because there's absolutely no dead space.
Yeah, when I BIAB, I crush really fine. I always adjust for ph whether I'm BIAB or "normal."

According to Kaiser, 100% conversion should be attainable with a little care. 95%+ is pretty much what you can get with a decent crush and pH in the right neighborhood.

I'm still working on BIAB rig plans in my head:
- incorporate a winch to lift the bag
-single vessel
- Just use an element directly in the kettle and recirculate, rather than an external RIMS. Sorta like many of the direct fired MLT's I've seen.
- Maybe even use a steamer basket for the grains lined with SS mesh. It may not get the same "squeeze" affect (effect?), but never have to worry about it ripping. Still easy to clean (just spray it off).

 
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Old 09-21-2009, 08:34 PM   #8
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I think 75% is pretty easily achievable if you use a fine crush and do a mashout. 83% sounds totally feasible (and awesome!).

You mention that you have a BIAB RIMS system. Very interesting...do you have any pics or a little more info on this? I can't brew outside in the winter here so I'm looking for some alternatives!

 
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Old 09-21-2009, 08:39 PM   #9
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I got 82% efficiency lastnight with BIAB. +1 on finding some type of winch to hold up the bag and let drip, my arms are usually pretty tired after holding a full bag of wet grain. A technique ive been recently using is to sparge in a seperate vessel, then do an extra sparge by holding the bag above the wort while a friend slowly pours a half gallon of 170 F water all over the bag....seems to work for me.

 
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Old 09-21-2009, 09:33 PM   #10
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Quote:
Originally Posted by Chips View Post
You mention that you have a BIAB RIMS system. Very interesting...do you have any pics or a little more info on this?
I have a typical 3 tier system that I sometimes BIAB. Need to get some more pics..

 
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