# BIAB - Water Retention Factor for Grains

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#### Imhoppy

##### Well-Known Member
I'm trying to understand the water retention issue for grains as I venture from extract brewing to BIAB. As with brewing, there are seemingly endless schemes and methods other brewers use to make an excellent batch of home brew. I enjoy the math behind the process, and am doing all the calculations myself, instead of using a black-box calculator that hides the details and just spits out the answers. Not for me.

Per the American Homebrewer's Association (AHA), it is commonly accepted that 1lb of grain absorbs 0.1 - 0.125 gallons of water. This range will vary depending on grains used and the total grain weight.

Per John Palmer's article, "BIAB - Tips from the Pros" the BIAB water retention factor, 0.25 quart per pound of grain (or 0.0625 gallons/lb) is typically half that of a standard mash 0.5 quart per pound (or 0.125 gallons/lb). So the "standard mash" value agrees with the AHA value.

So my first question, is why is the water retention factor for BIAB lower than a standard mash?

Per biabcalculator.com, the grain absorption value in BIAB Calculator defaults to 0.045 gallons/lb and assumes you do not squeeze the grain bag after it is left to drain by gravity. If you DO squeeze the grain bag, change the grain absorption value to around 0.031 gallons/lb.

Also, Palmer doesn't recommend squeezing the bag to wring every last drop, and in particular, he certainly does not recommend it when you are brewing dark beers.

My second question, is which value should be used (0.0625 or 0.045 gal/lb) for calculating the water retention, assuming a gravity drain only (assuming brewing on planet Earth and not someplace else, lol)?

My initial BIAB technique will be to use a pulley hoist and gravity drain into the brew kettle (size is 8 gallon, not big enough for a no-sparge 5 gallon batch) until the flow slows down sufficiently enough to transfer the grain bag into a brew bucket for a dunk sparge (with volume about the same as for the mash (@ 1.5 qts/lb) with enough to achieve the desired pre-boil volume). Then stir the grains and let soak for 10 minutes or so, then use the hoist and do another gravity drain. Then transfer the sparge water into the brew kettle and then continue on to boiling. I will use warm water, heated to about 100-120F (to cool the hot grains making them easier to handle after the sparge, and to capture some of the heat that would otherwise be wasted). Note this may increase the time a bit to reach boiling temperature. I'm sure this plan will be modified as I get more experience with BIAB. Like buying more brewing stuff. It always ends up that way.

I squeeze the bag personally. I hear it makes the beer take a little longer to clear up but it doesn't matter to me that much.

The numbers put out for grain absorption on a typical mash run may also include dead space etc factored in.... if you want balls on accurate numbers, unfortunately you really need to collect your own data!

just curious, why the obsession on grain absorption? LOL

far much more to worry about imo

I use a hoist and after letting it drain for a while I give it a 'good' squeeze, but not a 'thorough squeeze" and I don't sparge, I use .045 gal/lb which seems to work out well for me.
There is no way of really knowing for sure until you make a couple of batches and actually measure your results.

I found that factoring .08 gal/lb lets me hit my volume numbers. But I arrived at that figure empirically after several batches. I hoist out the bag, give it a light squeeze and let it drip into the kettle while I turn up the burner and bring the wort to a boil.

YMMV

So my first question, is why is the water retention factor for BIAB lower than a standard mash?

When a grain bag is suspended, the forces pushing on the sides of the bag will squeeze out more water than a typical mash tun. Moderate to aggressive manual squeezing will wring out more water.

Per biabcalculator.com, the grain absorption value in BIAB Calculator defaults to 0.045 gallons/lb and assumes you do not squeeze the grain bag after it is left to drain by gravity. If you DO squeeze the grain bag, change the grain absorption value to around 0.031 gallons/lb.

I like that site, but the defaults seem pretty aggressive. When I started I measured my first batch and came up with 0.05 gal/lb (I lost about 1/2 gal in a batch with 10 lbs of grain...I am pretty sure that was with squeezing). After a few batches I dialed that back a little just so I did not have to worry about squeezing the grain bag...squeezing a hot, wet and sticky bag seemed to go against the easy and simple brew day of BIAB. I think I count for around 0.07 gal/lb (BeerSmith uses the unit "liquid oz/oz" which I have set to 0.55).

just curious, why the obsession on grain absorption? LOL

Just so I can understand the basis for different values and to satisfy my never-ending curiosity on anything related to brewing. It helps me to better understand the technical details. This is only one of my numerous brewing obsessions. For example, drinking good home brew is another one lol.

I use 3 different constants when mashing. 1- MIAB is done in my 15 gal cooler tun and is .11 gal per pound. 2- BIAB full volume up to 16 lbs of grain .04 with a good squeeze. 3- BIAB full volume over 16 lbs up to 28 lbs is .06 because it;s hard to squeeze that amount as much. Your mileage my very.

Just so I can understand the basis for different values and to satisfy my never-ending curiosity on anything related to brewing. It helps me to better understand the technical details. This is only one of my numerous brewing obsessions. For example, drinking good home brew is another one lol.

But we all love our own children. That's probably why so many of us don't understand why others aren't as enthusiastic about our brews we share with them.

I only do small all grain batches. And I do BIAB. After I've gotten everything out that mashing and rinsing will do I lay the bag in a big strainer over my mash tun and then I mash the heck out of it for that last few drops.

So retention is going to depend on you more so than what a chart says. Keep notes on what you do and what you get, then further down the road you will be able to look back and know what works for you.

But we all love our own children. That's probably why so many of us don't understand why others aren't as enthusiastic about our brews we share with them.

I have mostly just shared my beer with my girlfriend over the past year. She loves 9% NEIPAs and 12% Maple Stouts. While I enjoy those as well, I would much rather have a 5% beer on tap and I would much rather brew a 80 IBU, 6.5% ABV Classic IPA, which are getting harder to find these days and she hates. Oh well...more beer for me to drink!!

just curious, why the obsession on grain absorption?
Just so I can understand the basis for different values and to satisfy my never-ending curiosity on anything related to brewing. It helps me to better understand the technical details. This is only one of my numerous brewing obsessions.
Grain absorption is a relatively minor factor in the whole brewing process!
Even with BIAB, after a pour over "sparge" or, a much better, 5x more gravity points rewarding "dunk sparge" in a large pail with 2-3 gallons of left behind brewing water.

Even at double the absorption amount of what you find acceptable (a pint of wort per pound of grist, instead of 8 oz a pint), it probably pales compared to the gallon or so of high gravity hopped wort you leave behind in your kettle and flush down the drain or dump into your compost pile.

I double batch sparge to raise my mash efficiency to around 85-90%.

After chilling, I reclaim at least another 2 quarts (that's 10% in a 5 gallon batch!) of leftover, high gravity, hopped wort from the kettle trub.
Now that's 10% (net) more BrewHouse (BH) efficiency! Yup!

I can suggest an experiment.
You need a dynamometer (one of those cheap suitcase weight scale I think would do).

Put your grist inside your bag, you know its weight. Mix water. Mash. Extract the bag but keep the dynamometer hooked to the hoist, so that it measures the weight.

When you extract the grain bag, let it drain as you would normally do, (and/or squeeze as you would normally do). At this point, read the weight on the dynamometer, and subtract the original weight of the dried grist.

A liter water weights 1 kg but a litre wort weights more, depending on your pre-boil density. Just use the density as a divider.

Let's say you have a 5 kg grist and a 9,5 kg weight indicated by the dynamometer, meaning you have 4,5 kg excess weight, and your pre-boil wort is 1,045, that means you have 4,5 divided by 1,045 = 4,30 litres of wort trapped in your grist. You could "squeeze" at this point and re-measure the weight and note it to know how much wort is "squeezing" worth.

An example of cheap scale:
https://www.amazon.it/BILANCIA-DIGI...AMOMETRO/dp/B07951TPXH/ref=asc_df_B07951TPXH/

@IslandLizard Good point, not just what you put in but also what you get out and don't leave behind. Big hoppy beers suck up the liquor and cause losses in the fermenter.

not just what you put in but also what you get out and don't leave behind.
You're getting it!
This is about the net volume and gravity in the fermenter.

Big hoppy beers suck up the liquor and cause losses in the fermenter.
That's why I'm a big proponent of cold crashing (under CO2 of course, or whenever possible).

Even with an 8-12 oz dry hop charge in a 5.5 gallon batch, I only have 1/2 gallon of compacted trub on the very bottom, that way. I know that's all there is, because I dump the whole leftover yeast/trub cake it into a 1/2 gallon pickle jar.

You're getting it!
This is about the net volume and gravity in the fermenter.
I disagree. What you are talking about is brewhouse efficiency. What is really important is packaged efficiency: net volume and gravity in containers that you can consume (or otherwise make productive use of.)

For example: If I leave 1 gallon of trub in the BK, and leave 1/2 gal of trub in the fermenter, I have a lower brewhouse efficiency than if I only leave 1/2 gal in the BK but leave 1 gal in the fermenter. But, the end-to-end efficiency is the same - I get the same amount of beer at the same FG and ABV.

Brew on

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What is really important is packaged efficiency
Of course, the final packaged volume (and quality of it) is what ultimately counts.

Separating/recovering as much wort and beer from the grist and trub at every respective stage is the central idea to that.

For 10lb of grain I use 8.25 gallon of water to end up with ~5.5 gallon of final liquid in the fermenter. I boil for 60 minutes.

What is really important is packaged efficiency: net volume and gravity in containers that you can consume (or otherwise make productive use of.)

I need to get better about measuring and recording my packaged volume. For a while I was weighing my kegs and I realized that when I was targeting 5.25 gals into a fermenter, I was often getting about 4.75 gals into a keg. So I changed my target to 5.5 gals into the fermenter. The scale I was using (a bathroom scale) did not seem that accurate at that weight range and has since died. I have been meaning to pick up a postal type scale. I am not quite sure what my losses are for a typical IPA or NEIPA.

You just have to figure out your system. Personally, I find online calculators to be too low for grain absorption for my BIAB system. After a few brew days you can start to average out your absorption rate and plan accordingly.

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