Grain Bed Water Absorbtion amounts?

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CraigKing

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Did a breakfast stout yesterday that had the better part of 20lbs of grain in it. I used 6gals of strike water, and sparged with another 1gal. I barely got over 5gals of wort. I checked my OG and it wasn't too far off, so I used more water to sparge.

In total, 7.5gals of water went into my MT. I only got 5.5gals back out. Does this sound normal? After my boil, I only had 4.5gals. Would 20lbs of grain absorb that much water? When I dumped my MT, there certainly wasn't like a pocket of water that had been trapped.
 
In total, 7.5gals of water went into my MT. I only got 5.5gals back out. Does this sound normal?.....Would 20lbs of grain absorb that much water?

I normally assume ~0.5 qts/lb for absorption. Using your numbers:

20 lbs grain * 0.5 qts/lb = 10 qts = 2.5 gal water absorbed


Add in dead space in your tun and you actually came out better than average.
 
Wow, that's interesting. I didn't realize there was that much absorption!

Thanks for the calculator.


Also, just realized I spelled absorption wrong in my title. :eek:
 
I've been brewing a long time... always had problems with the default absorption values of around 0.12-0.13 gallons/pound. I think this is due to people measuring the entire volume they are missing and forgetting about losses. The grain absorption ITSELF will likely be lower, PLUS losses.

I now use 0.10 gal/lb for barley mashes (plus a constant dead-space loss) and nail my volumes perfectly. This would equate to 2.0 gallons per your 20 lbs of grain, which fits your observation assuming no/minimal losses elsewhere. It will also depend how long you let the tun drip after draining, let experimentation be your guide. You have 1 data point now. 0.10 gal/lb.

When I use any amount of flaked grains, I will increase this to 0.11, possibly 0.12 if it's a large percentage of the grist.

If you are grinding extremely fine (like BIABers often do), you should go even lower, around 0.08 gal/lb.
 
I always figure 1 pint of absorbtion per pound of grain. That always comes out pretty close for me.
 
@gotpushrods

Even lower. I typically see ~0.045 gallons lost per pound to absorption.

It's not the fine milling which reduces the absorbed volumes seen with BIAB. It is the added lautering efficiency via gravity and/or squeezing that does that. A finer grist may help but it is not the main player.
 
I agree with everything said above. Ultimately these values are only estimates used until you can effectively predict your losses for your system.

After that, everything should be consistent.
 
If I have to figure a value off the top of my head if I can't get to a mash calculator, I usually see a return of 45% of my mash volume (per my system). So if I mash with 9 gal, I can expect ~ 4 gallons of wort. Meaning I need to spare with an additional 9 gal to reach my pre-boil volume of 13 gal (since there cannot be anymore grain absorption)
 
So my next question is, if I'm following a recipe and the recipe states that it is a 5gal batch, and I do the calculations to determine the total number of gallons needed to mash, is that going to affect the OG?

Like this breakfast stout I made, it was a 5gal batch, but I needed 7.5-8gals of water in the mash. Is it assumed that the OG was based on mashing with 7.5-8gals of water too?
 
Recipes are based on brewhouse efficiency and should be stated in the recipe. You need to adjust recipes based on your own brewhouse efficiency. Doesn't matter how you reach that final number.

If the volume and gravity of the wort in the FV are known you can calculate the BH efficiency. If you spare with 1,2,5,10 or 0 gallons it does not matter. The recipe only tells the end point.

eg: 5.5 gallon batch size at 1.049 OG using 9.44lbs of grain on my last brew's recipe equated to a planned BH efficiency at 80%

If you were following this recipe on your system the grains would be adjusted based on how efficient your setup is. More efficient, less grains used. Less efficient more grains used. Scaling a recipe for size of the batch or projected efficiency is easy enough.
 
To add to what Gavin said: when following another brewer's recipe what you want to pay attention to are post boil gravity (a ratio), grain bill ratios, and hop bitterness ratios. The actual quantities of ingredients to produce the same wort from one brew system to the next could be completely different depending on a number of factors. It's up to you as the brewer to figure out what those factors are for your system. IE extract efficiency, brew house efficiency, volume losses, boil off rate, etc.

Like this breakfast stout I made, it was a 5gal batch, but I needed 7.5-8gals of water in the mash. Is it assumed that the OG was based on mashing with 7.5-8gals of water too?

I wouldn't look at it that way. I'd say the 7.5 to 8 gallons of water was assumed based on the target OG and a some efficiency.
 
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