# Question: small scale measurement

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#### pedrovic

##### Member
Hello,
I need to measure the most accurate grain absorption in my BIAB system, but the total grain weight I currently have allows only a regular batch and a leftover that I thought of doing this measurement, only reducing the scale to that.
I learned an equation (initial volume - volume post_mash / grain weight) and I was wondering if a small-scale measurement would give me a result equal to use the normal volume of a regular mash.
Example: calculate the grain absorption using only 100g (3.5 oz) of grain in 1 liter (1 quart) of water give me a usefull grain absorption result similar to a large scale calculation?
Has anyone ever done that?
Thank you.

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#### DBhomebrew

##### Well-Known Member
I haven't tried it, but in my theoretical estimation it would not.

For example, with BIAB the size and weight of the grain bed causes the bottom of the bag to distend downward with the walls of the bag pulling inward. This adds a little natural squeeze to the effect of gravity.

If you're going for most accurate...

I have attained very repeatable results by measuring the height of the wort with a stainless ruler to the nearest millimeter. This is dropped into the formula for a cylinder and in my kettle is accurate to the nearest ~1.7oz. My pre-boil volume is regularly within a few hundredths of gallon of the target.

Don't forget to account for temp induced expansion. Volume taken at mash temps are adjusted by 2.7% over room temp, boil by 4%.

#### doug293cz

##### BIABer, Beer Math Nerd, ePanel Designer, Pilot
Staff member
Mod
HBT Supporter
You could measure the absorption on a mini-batch, but then you have to go back and demonstrate that the mini-batch draining gives the same absorption rate as a full batch. The mini-batch will have a lot lower grain weight in the draining bag, so less squeezing from the bag being pulled taunt by the weight of the grain. Thus it is likely that the mini-mash may end up with a higher absorption. And you have to do the full mash measurement anyway, to confirm the validity or invalidity of the mini-mash method.

Unless you are doing an academic study on the effects of bag size and grain weight on free draining of BIAB, you are better off just measuring the actual runoff volume the way @DBhomebrew suggests. And don't forget to correct for temperature expansion of the hot wort. Here is a table where the left column shows the temp of the measured wort, and the right shows the multiplier to use to converted to the volume at room temp (68°F.)
Brew on

OP
OP
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#### pedrovic

##### Member
Wow, thank you very much @DBhomebrew and @doug293cz for the information! I will read and reread very carefully.

I am not doing an academic study, but I am happy to know that my curiosity about the subject looks like this.
I'm just an old homebrewer who sometimes asks too many questions :-D
Cheers!

#### hotbeer

##### Opinionated Newb
HBT Supporter
I just weigh everything going in and then everything coming out, including the stuff I'm throwing out.

Then it's a cinch to figure what is was for that batch and might be for future batches.

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#### pedrovic

##### Member
@hotbeer do you measure the weight difference?

#### hotbeer

##### Opinionated Newb
HBT Supporter
@hotbeer do you measure the weight difference?
Just with respect to the grain. I measure the weight of my malts going into the mash and then after draining everything from them I weigh them again and find the difference. That pretty much is my loss due to grain absorption isn't it?

I know the tare for my various vessels used. But if I use something different, the tare function on the scale makes it easy enough.

#### doug293cz

##### BIABer, Beer Math Nerd, ePanel Designer, Pilot
Staff member
Mod
HBT Supporter
Just with respect to the grain. I measure the weight of my malts going into the mash and then after draining everything from them I weigh them again and find the difference. That pretty much is my loss due to grain absorption isn't it?

I know the tare for my various vessels used. But if I use something different, the tare function on the scale makes it easy enough.
In a word, no. It's much more involved than that. I will write more later, when I am not in the middle of brewing.

Brew on

#### IslandLizard

##### Progressive Brewing
Staff member
Mod
HBT Supporter
Just with respect to the grain. I measure the weight of my malts going into the mash and then after draining everything from them I weigh them again and find the difference. That pretty much is my loss due to grain absorption isn't it?
Not quite!
For example you'll need to add the weight of the extracted sugars and dextrins back in, those are now in your lautered wort. Also dust and other small particles that made it through. Most of that will settle out in your kettle trub.

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#### pedrovic

##### Member
What I understood in the previous responses is that there are several factors that must be taken into account when measuring. The mash water expansion multipliers are a new concept for me and I wanted to understand more.

OP
OP
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#### pedrovic

##### Member
You could measure the absorption on a mini-batch, but then you have to go back and demonstrate that the mini-batch draining gives the same absorption rate as a full batch. The mini-batch will have a lot lower grain weight in the draining bag, so less squeezing from the bag being pulled taunt by the weight of the grain. Thus it is likely that the mini-mash may end up with a higher absorption. And you have to do the full mash measurement anyway, to confirm the validity or invalidity of the mini-mash method.

Unless you are doing an academic study on the effects of bag size and grain weight on free draining of BIAB, you are better off just measuring the actual runoff volume the way @DBhomebrew suggests. And don't forget to correct for temperature expansion of the hot wort. Here is a table where the left column shows the temp of the measured wort, and the right shows the multiplier to use to converted to the volume at room temp (68°F.)
Brew on
About this table, how I can use? Multiplying the temp (°F) by the multiplier? After that, I must add to the pre-boil volume (gal)? Thanks

#### IslandLizard

##### Progressive Brewing
Staff member
Mod
HBT Supporter
It adjusts the measured volume at its current temp to its actual volume at a (standard) reference temp, 68F (20C), IIRC. So you can compare actual volumes at different temps.

#### DBhomebrew

##### Well-Known Member
About this table, how I can use? Multiplying the temp (°F) by the multiplier? After that, I must add to the pre-boil volume (gal)? Thanks

Take your measured volume and multiply that by the appropriate amount in the table to find your standardized volume to be used in further formulae such as finding your lauter efficiency or absorption.

It's a matter of apples and oranges. Heat 1G of room temp water to 212° and it will be ~1.04 gallons.

#### hotbeer

##### Opinionated Newb
HBT Supporter
Not quite!
For example you'll need to add the weight of the extracted sugars and dextrins back in, those are now in your lautered wort. Also dust and other small particles that made it through. Most of that will settle out in your kettle trub.
Not certain I fully understand. I thought grain absorption was all about just figuring water losses at the mash time so that you wind up with the amount of wort you wish to start your boil with.

Of course there are losses too for evaporation and for solids from the mash process that make their way with the wort to the boil kettle. Those get accounted for at that time. Just like the losses in the FV for trub, yeast, hydrometer samples and etc.

All these just get tallied up and used to make better estimates for how much total water will be needed for subsequent batches.

So maybe I'm looking from too simplistic a viewpoint.

#### BrewnWKopperKat

##### .
 From a different perspective If I have ​1.04 gal water at of 212°F.​ that same amount of water at 68°F is ​1.04 * .96​​or roughly one gallon (multiplier for calculating water volume at room temp (68°F.)

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