Confused on ABV & ABW

[gad]

G'day
I'm a little confused on ABV's & ABW's & hoping for a little clarification.
Most beer brewing books I have read say to subtract the Final SG from the Sart SG & multiply by .14 to give you the Alcohol as a percentage (I have also read elsewhere to use .131).
(is this the same as ABW or ABV or neither?)

The calculator in the Calc's section here multiplies the same SG by .129 which I believe gives you the ABV.
I also read that to convert ABW to ABV you divide the ABW by 0.79. To convert the ABV to ABW you multiply the ABV by 0.79.

If I had (hyperthetical) a start SG of 1040 & a Final SG of 1010 = 30 x 0.14 = 4.2%
If I had (hyperthetical) a start SG of 1040 & a Final SG of 1010 = 30 x 0.129 = 3.87%

Or should I just forget that beer making alcohol by percentage stuff?
It confuses me as that's how I work out the percentage of alcohol in my beers & thought it would be the same when doing a wash for spirits.

Just trying to get my head around this, it confuses my feeble little mind ...... Thanks

[blond.chap]

Hey mate, I understand your confusion, I only just worked this out.

First off, the conversion is slightly more complicated than that, check the glossary in the newbie's corner for the real formula for converting between them. Dividing by 0.79 only works roughly for low alcohol percentages.

What you read with a spirit hydrometer is abw, what bottles generally say is ABV.

For the calculation from gravities to %, I use calculators on the net, couldn't tell you the formula. I would expect this gives ABW, but couldn't tell you for sure.

Hope that helps.

[gad]

Thanks blonde.chap. That will help me get my head around it. Cheers.

[invisigoth]

What you read with a spirit hydrometer is abw, what bottles generally say is ABV.

erm.. both my spirit hydros use the tralles scale which is abv not abw :shifty:

[SBB]

Geeeze now I'm getting confused, isn't what we use to measure our SG and FG in washes called a "Hydrometer", and what we use to measure out finished spirit called a Alcometer? A Hydrometer measures specific gratify. As far as Im aware all the Alcometers Ive seen read in ABV, Alcohol by Volume the same as whats on a bottle.

[googe]

It's clutching at straws unless your a commercial distiller. In hobby mode them.differences are naught. I think your on the money sbb, they make different measurement apparatus for a.reason.

[blond.chap]

Ah you're right invisigoth, I had some circular logic going. My spirit hydrometer is ABV.

SBB, hydrometers and alcometers (also called spirit hydrometer or alcohol meter) are basically the same tool, just with different ranges. A spirit hydrometer reads density as well, but has conversions to ABV on it. If your spirit hydrometer was written in gravity, 100%ABV would read 0.79, and 0%ABV would be 1.000.

[googe]

Like why they make metric and imperial tools, nuts ain't just nuts.

[invisigoth]

Like why they make metric and imperial tools, nuts ain't just nuts.

look on the bright side googe.. at least he hasn't suggested using a pycnometer to calculate abv! :laughing-rolling:

[gad]

OK, not any less confused lol

So, is, as my beer making books say, Original SG - Final SG x .14 = content of alcohol by percentage the same as ABV (alcohol by Volume) ? (I'm thinking it must be).

I'm also still confused that the old beer making books multiply the wash by .14 and Wash calculators from the Calculators section multiplies the wash by .129.

The reason I'm trying to work this out is because I'm having some trouble getting a decent amount of alcohol from my still runs & it was suggested in another thread that the "final ethanol conc'n should be less than 10-12% abv". So I either want to be able to dismiss this as the cause or identify it as the cause.

So, for example, if the start SG is1090 & final SG is 990 then using .14 = 14%, .129 = 12.9%. It's a fair difference & I just want to know that I'm working it out right.

Or should I just use the Wash calculator & trust it? Thoughts? Thanks. :pray:

PS - after a thought & a little working out, the old beer making books may be wrong. On the sheet that came with the hydrometer they have a table with potential alcohol (% Vol) on it. Their example gives a final 10.5% Vol. Those same SG's Calculated using x .14 gives 11.2% & x .129 gives 10.32% so I might just ditch using .14.

[SBB]

Have you tried using something like this to work out your wash ABV. http://homedistiller.org/calcs/sugar_sg there are a heap more calculators on that page for other purposes.

[meerkat]

The factors of 0.14, 0.131 and 0.129 are definitely aimed at giving an ABV value. Theoretically the actual factor will depend on the alcohol stength (i.e. it is not a true constant) Theoretically (again!) it will increase slightly as the alcohol strength increases.

However, it will also be affected by practical things like your fermentation efficiency - some of your sugar will be used for yeast growth rather than the generation of alcohol. This will depend on your particular setup and makes it hard to pinpoint one number.

The factor will also depend on what other components are present - i.e. other than sugar, water and ethanol. This may explain why the values used in beer brewing do not apply to making whisky or neutral spirit.

The value of 0.129 looks like a reasonable compromise when making low alcohol wines. Your value of 0.131 may be a better estimate if you are aiming for a 12% abv starting from a clear wash. I agree that 0.14 is very optimistic in this case (although it may apply to making beer).

For converting between ABV and ABW for values between 0% and 12% ABV a constant value of 0.80 will give you negligible errors. As the strength increases beyond 12% the accuracy decreases and certainly by the time you get to 30% you will get errors that will get your tax inspector very agitated.

[googe]

I would think 0.129 has been chosen so to have a start point were anything different in the + side is a bonuse in the long run.

[gad]

Thank you very much for clearing that up for me guys, very much appreciated.