Weight of Beer vs. Water

I want to approximate the weight of some beer per gal, so that I can approximate splitting between two kegs by weight.

Can I assume that the rough equivalent of what DME it would take to replicate my FG would be close?

Ethanol is the other major part of the equation, but I assume that's mostly a wash, as it's probably close enough to the weight of water to be irrelevant for generalities.

So, e.g....

1 gal water = apx. 8.33 lbs
DME needed to make 1 gal of 1.012 SG wort = apx. 124 g = apx. 0.27 lbs

Thus, I expect 1 gal of 1.012 FG beer = apx. 8.6 lbs

Right??? or is this all wrong?

Why don't you weigh a glass of beer and then weigh a glass of water?

Ok so i'm gonna try and science. (warning im an anthropologist)

It all depends on the FG of the beer. A beer with FG of 1.010 will weigh 1.010 kg / liter, 1.006 will weigh 1.006 / liter and so on

If this isn't the case then I don't understand SG's.

ol-hazza said:

Ok so i'm gonna try and science.

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hahaha. this!!!

ol-hazza said:

Ok so i'm gonna try and science. (warning im an anthropologist)

It all depends on the FG of the beer. A beer with FG of 1.010 will weigh 1.010 kg / liter, 1.006 will weigh 1.006 / liter and so on

If this isn't the case then I don't understand SG's.

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Yes, at least in my understanding also. Keep in mind it's a ratio, so your sample weighs whatever your SG reading is times the weight of the sample if it were distilled water.

So if a gallon of distilled water weighs 8.33 pounds, a gallon of 1.006 SG liquid should weigh (8.33 x 1.006) or 8.38 pounds. For 5 gallons, distilled water would weigh 41.65 pounds and 1.006 beer should weigh 41.90 pounds. Or roughly 4 ounces difference in 5 gallons. Not really enough to matter in my opinion.

I just read this in Science for Ermehrica.
Water has a weight of exactly Bud Light at 32F while beer has a shifting weight depending on how good it is.

mertherflerkern science, Ermehrica. science.

Billy-Klubb said:

I just read this in Science for Ermehrica.
Water has a weight of exactly Bud Light at 32F while beer has a shifting weight depending on how good it is.

mertherflerkern science, Ermehrica. science.

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.

Yeah for science.

Remember, kids, "a pint's a pound the world around." You'd have to need some exacting precision for your purposes for this approximation to not be good enough. Or some pretty crazy high FG beer.

GuldTuborg said:

Yeah for science.

Remember, kids, "a pint's a pound the world around." You'd have to need some exacting precision for your purposes for this approximation to not be good enough. Or some pretty crazy high FG beer.

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A pint of water is a pound only in America. An Imperial pint is 20 ozs, or 10 lbs for a gallon of water.

....... And since the US fluid ounce is about 4% larger than everyone elses, a 16 oz pint is about 5% heavier than a pound, TAK is probably close/right at 8.33 lbs to a gallon.

1.012 specific gravity is 8.445549116lbs/gallon. Give or take a millionth.

Calder said:

A pint of water is a pound only in America.

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Good catch - I forgot about this what with the rest of the world so metric heavy.

I thought about weighing a glass of water vs. beer, but I figure my scale isn't that accurate, and the margin of error will just compound as I scale up to five gallons.

brick_haus said:

1.012 specific gravity is 8.445549116lbs/gallon. Give or take a millionth.

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Can you show your math please.

TAK said:

Can you show your math please.

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1.012 SG = 1.012 kg/L

1.012 kg = 2.23108 Lbs

1.012 SG = 2.23108 Lbs/L

1 Gal = 3.78541 L

2.23108 Lbs/L X 3.78541 L/Gal

1.012 SG = 8.4455... Lbs/Gal

There are 42.23 lbs of beer in your 5 gal corny keg

I believe him. I don't know why, but I do, yo.

Do I understand correctly that the SG readings we take with a hydrometer or refractometer doesn't actually give an accurate representation of the residual sugars because the alcohol distorts the reading? So there would need to be some sort of correction for that, if you are going to calculate the weight based on the residual sugars. Or does the presence of alcohol offset the weight the same way it does the gravity?

Wrong post.

signpost said:

Do I understand correctly that the SG readings we take with a hydrometer or refractometer doesn't actually give an accurate representation of the residual sugars because the alcohol distorts the reading?

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Not exactly, but that's because they don't measure sugar at all. A hydrometer measures density, and a refractometer the refractive index, of a liquid. Everything else we get from assumptions about properly made worts and calculations. Either that or we have just learned how to correlate densities and refractive indexes to wort/beer properties well enough to inform our brewing decisions.

signpost said:

So there would need to be some sort of correction for that, if you are going to calculate the weight based on the residual sugars. Or does the presence of alcohol offset the weight the same way it does the gravity?

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OP isn't calculating weight based of residual sugar. He's calculating weight based off the density and volume of the beer, for which there is a direct relation.

I could be wrong, but I get the feeling these devices work in the exact opposite direction you think they do. That's not a criticism - I'm just trying to bring a little clarity to the situation.

Right, I understood those tools measure density, which we then apply to homebrewing as a way to understand how much sugar is in solution. I also understand that a beer that ferments out to a SG of 1.000 (same as distilled water) still likely has some sugar in solution, but the density of the sugar is balanced by that of the alcohol.

But I see now that it doesn't matter how various parts of the solution balance each other to reach a certain density. The density is directly related to the weight, regardless of what the substance is.

This all just popped in my head as possibly having an impact on the calculation in the thread and I wanted to be sure it wasn't something that was being overlooked. Luckily, some of you know much more about how to calculate this stuff than I do.

signpost said:

Right, I understood those tools measure density, which we then apply to homebrewing as a way to understand how much sugar is in solution. I also understand that a beer that ferments out to a SG of 1.000 (same as distilled water) still likely has some sugar in solution, but the density of the sugar is balanced by that of the alcohol.

But I see now that it doesn't matter how various parts of the solution balance each other to reach a certain density. The density is directly related to the weight, regardless of what the substance is.

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Exactly. Sorry for jumping to conclusions. I've heard enough people talk about how a hydrometer can magically measure sugars directly around here that I sometimes assume that's what someone else is thinking (in situations like this). Anyway...cheers.