Calculate weight of beer per gallon

[Rob2010SS]

Anyone know the formula for this? I saw @Qhrumphf discussing it in another thread, but the way it was worded was a bit confusing...

 

[Birrofilo]

For what I understand, you should simply measure the density of your beer.
The density is the weight of the beer compared to the weight of water.

So if your beer has a final density of 1,010 that means that a litre weights 1,010 kg.

You can then convert to any unit of volume and weights, such as cubic cubites, amphorae, drachmae etc.

 

[Qhrumphf]

It'll depend on temperature. At 70F, water is about 8.33 pounds per gallon. At 40F it's more like 8.35. There are calculators abound on the internet that can give you the weight of water (often in multiple formats, lb/gal, kg/l, etc) for a given temperature.

Once you have your water weight, multiply that by your specific gravity and you have your beer weight. So 1 gallon of beer at 70F and at 1.010 is 8.33*1.010 or 8.41 pounds.

 

[Tobor_8thMan]

Or, asking about ABW?

 

[Qhrumphf]

At 4°C/39.2°F, water is at its most dense and at that point water is 1kg/l (in utmost technical sense it's 0.9998kg/l, but you'll almost always see that rounded to 1), and your beer would be it's specific gravity in kg/l as above. Warmer or colder and the density of water (and beer) will go down (and it's weight per a given volume will go down as well, though note that a given samples mass/weight wouldn't change with temperature, rather its volume is what changes).

Where I'm not sure any more is once you get sub-32F, where water expands significantly as ice but beer, thanks to ethanol, can remain liquid until a proportionately lower temp (I'd have to look it up but IIRC a 5% ABV beer shouldn't freeze until 27 or 28F).

 

[Rob2010SS]

Ok, I'm following now..

So, beer of 1.015 @ 35*F should weigh...

8.35 * 1.015 = 8.47 lbs/gal

Therefore, to fill a 5 gallon corny to the max, assuming the keg I'm using weighs 9.5 lbs empty...

8.47 * 5 gallons = 42.35 beer weight
42.35 + 9.5 = 51.85 lbs for full corny

I had read that the weight of a full keg at one point was 50 lbs, so that's the number I've been going with. However, I want to make sure I'm maximizing my kegs to their full potential. I don't want to waste any precious liquid!

 

[day_trippr]

A few years ago HBT member @kaljade created a small spreadsheet that takes into account Empty Keg Weight, Fill Keg Weight, Beer Temperature, Beer Gravity, Carbonation level (most post-fermentation beers will carry between 0.6 to 0.8 volumes of CO2 - which makes for extra mass), and Altitude (which I guess adjusts the pressure), to calculate the fill volume.

It's way more accurate than what I was doing before - I just had a full 5 gallon keg kick with just 4 ounces indicated remaining from my tap list manager, which is pretty darned accurate flow metering vs calculations...

I believe the first post in the linked thread has a pointer to his latest version, but check the last post to verify the MD5 checksums match the expected value...

Cheers!

 

[Tobor_8thMan]

And then there is

https://www.morebeer.com/products/plaato-keg-management-system.html

 

[Rob2010SS]

And then there is

https://www.morebeer.com/products/plaato-keg-management-system.html

Yeah, I have one of these in my kegerator but I don't want to move it. Does it work well for filling kegs?

 

[Bramling Cross]

I had read that the weight of a full keg at one point was 50 lbs, so that's the number I've been going with.

It depends on the beer. As an undergraduate student I worked on a beer delivery truck and I can assure you that a keg of Bert Grants weighed a lot more than a keg of Coors Light and a keg of Shakespeare Stout, well, even as a dumb kid with more muscles than brains, I learned to respect those kegs and make certain that I had a plan and a clear path before trying to lift them.

 

[Tobor_8thMan]

DIY project in the March-April 2021 "Brew Your Own" magazine "Keg Level Sensor" with the components built into the keg lid. Most interesting.

 

[day_trippr]

We have that here, actually...

https://www.homebrewtalk.com/threads/flite-keg-level-temperature-and-pressure-sensor.687681/
My two issues are the relative environmental hostility inside the keg vs a good flowmeter outside, and the need for so many equipped lids.
I have 16 kegs, there's no way I'm breaching an O2 tight keg to swap lids, and there have been times where all 16 kegs had beer in them, so trying to subset isn't going to work reliably.

Meanwhile I had a keg kick today with -2 ounces indicated in RaspberryPints. SF800 meters are awesome

Cheers!

 

[Tobor_8thMan]

Yep, you are correct. Seems BYO "stole" from HBT.

 

[day_trippr]

I don't have a subscription but I presume the author is the same Mister Flite

Cheers!

 

[Tobor_8thMan]

BYO Projects article is by Derrick Marlow.

 

[UncleD]

BYO Projects article is by Derrick Marlow.

Call me Mister Flite, haha! Yeah I wrote the article for BYO.

 

[Kee]

So, this discussion begs the question: What scales should I be using to weight my kegs?

 

[Rob2010SS]

So, this discussion begs the question: What scales should I be using to weight my kegs?

I use a postal scale. I got it as a gift but if you look for something like that on Amazon, should get you there

 

[Unicorn_Platypus]

It'll depend on temperature. At 70F, water is about 8.33 pounds per gallon. At 40F it's more like 8.35. There are calculators abound on the internet that can give you the weight of water (often in multiple formats, lb/gal, kg/l, etc) for a given temperature.

Once you have your water weight, multiply that by your specific gravity and you have your beer weight. So 1 gallon of beer at 70F and at 1.010 is 8.33*1.010 or 8.41 pounds.

Is this off final gravity or original gravity?

Assuming it's final gravity

 

[sibelman]

to the max,

pretty darned accurate

Old thread.

Final for sure.

Given that a "full" corny can be somewhat over 5 gallons, the small density difference re temperature seems important more as a technical matter, and of little practical significance.

 

[MaxStout]

Is this off final gravity or original gravity?

Assuming it's final gravity

The example @Qhrumphf gave stated 1.010, so I'll stick my neck out and assume it's FG, as well. Unless someone likes to make really, really, weak beer.

 

[sibelman]

These calculations are about the beer (fully fermented or not) that's going into a keg sitting on a scale. It's about the gravity at the time the keg is being filled, original, final, or in between.

 

[Unicorn_Platypus]

That's what I figured

I've been conservatively going with 8.3 pounds per gallon when I fill my kegs regardless of gravity. Figure if my fills are marginally light that's close enough.

So does that mean a beer takes up more volume after fermentation than it does before fermentation since it's denser before it ferments? Never thought about it, but I guess that makes sense

 

[khannon]

Also, if you are force carbing, leaving a little room to maximize surface area will result in a quicker carbonation. This helps to get to drinking the beer a little quicker.

 

[Unicorn_Platypus]

Also, if you are force carbing, leaving a little room to maximize surface area will result in a quicker carbonation. This helps to get to drinking the beer a little quicker.

I prime my kegs with sugar nowadays , but like to leave a little headspace so I can fit up to 16oz of priming sugar solution. I inject it via the gas post and my gas diptubes are trimmed, but still like to leave a little extra to account for thermal expansion.

My kegs to the brim hold about 20 oz over 5 gallon

 

[sibelman]

more volume after fermentation

No, i don't think so. Mass and (I'm surmising) volume are lost as CO2 departs. Less dense, but almost certainly not, er, bigger. More mathy answers may be forthcoming. Doug?

 

[FloppyKnockers]

How I calculate the wait time of beer per gallon is I normally wait until 5 or so. On the weekends you can start earlier, but I make sure to drink some water so I'm not useless the next day.

 

[day_trippr]

Wort will lose mass through fermentation, but will gain mass back through conditioning. It would take someone like our resident physics dude @doug293cz to calculate the net change but I suspect fermentation loss exceeds carbonation gain...especially as the OG increases...

Cheers!

 

[sibelman]

will gain mass back through conditioning

I wonder whether either fermentation or carbonation significantly affect wort/beer volume or mass. I'm not sure what "significantly" means, of course. I haven't noted other conversation here about accounting for these (small, I think) effects in homebrewing tasks/decisions.

Rough semi-intuitive take: a 5-lb CO2 bottle lasts "quite a while" (very quantitative...NOT!) so mass effect per keg is "clearly" in ounces. A cup of sugar or malt weighs a few ounces. The beer level in a primed bottle doesn't noticeably change as carbonation occurs. Therefore, the mass and volume effect of carbonation is small-ish. Fermentation too?

Still, it would be interesting to see numbers from a physics/chemistry-informed source.

 

[day_trippr]

I don't think anyone was claiming truly profound changes to mass here

[edit] Although...found this on the Brewing Reddit. I can't vouch for it but there were other posts in the same thread that confirmed/amplified it...

"Turns out for five gallons/18.9 L of 1.060 wort at 75% apparent attenuation, 449.1 L/ 15.86 cubic feet/ 118.64 gal of CO2 is produced (standard temperature and pressure. This amounts to 0.88 kg/ 1.94 lb of CO2!"

For sure that's a lot more mass shed than would be gained if it's then brought up to 2.5 volumes of CO2...

Cheers!