ABV using hydrometer???

[Wolfman]

ive heard i can determine the alcoholic percentage of a brew using the gravity reading on my hydrometer..if this is true,how can i get an ABV percentage??

Wolfman

[john_drummer]

AFIAK there are two ways...

1) ((OG - FG) / 7.46) + 0.5 - this one comes from Coopers kits - 30/7.46 = 4.02 + 0.5 = 4.52 %ABV
2) ((OG-FG) * 131) - not sure where I got this one from - (1.040 - 1.010) * 131 = 3.93% ABV

where (1) OG & FG are expressed as 1040 / 1010 respectively
or (2) they are 1.040 and 1.010 respectively

obviously there's a big difference here... can anyone help me out? maybe it's the "+ 0.5" on the Coopers formula, take this off & they're fairly close...

[Spud395]

Spoke to a head brewer/owner of a microbrewery about this.
He must determine the ABV of his beer to pay taxes on it (I'm Irish, so is he, it may be different over there)

Anyway he uses OG-FG X 131, now sometimes he uses 130 or 129 depending on the gravity readings, but I think he said that was for stronger brews.
If he's wrong with his ABV it costs him extra, so I stick with his calc's

[oldbloke]

ive heard i can determine the alcoholic percentage of a brew using the gravity reading on my hydrometer..if this is true,how can i get an ABV percentage??

Wolfman

You take a gravity reading at the start, another at the end, the difference is due to the amount of sugar that's been changed to alcohol. However, presence of stuff other than water and alcohol in the solution means it's not exact. Most people use the calculations mentioned already in this thread. You might want to look at the table here: http://www.brsquared.org/wine/CalcInfo/HydSugAl.htm
...and don't forget to correct for temperature...
...and check your hydrometer does read 0 in pure water...

Personally, I use tried and trusted recipes and don't worry about the exact %
But when I do want to tweak it, I more often work by calculating how much sugar I have at the start - as I always ferment to complete dryness, it all goes to alcohol, and, roughly:
100grams of sugar in 1 gallon gives 1% ABV.
OK it's not so handy with beer where you may not have to hand the sugar content of your malt, but for TurboCider etc, where the sugar is listed on the carton, it's great.
And for country wine, there's a list around (by Moley on The HomeBrew Forum) of the typical sugar content of a wide range of fruits etc, to which you add the extra sugar you chucked in...
(but for those I just use existing recipes as far as the sugar content goes - it'll come out somewhere in the 12-16 % range)

[vacant]

Here are the HMRC calculations. See sections 30 and 31.

If you use cane sugar directly (rather than a solution) for priming and it fully ferments then half that weight results in alcohol. 85g sugar -> 42g alcohol so volume is 42 / 0.79 = 53ml. In 23l, that's another .23%

[Seivad]

Going back to the Coopers Kit method (i.e. adding 0.5%), this seems way too much to me to adjust for the impact of priming sugars. Ignore this and the two methods john_drummer suggests are very similar. I use the first but without the 0.5%.

[adomant]

HMRC use this:

(OG – PG) x f = a% ABV
Where:
• OG is the original gravity of the beer
• PG is the present gravity of the beer
• a is the beer's alcoholic strength, and
• f is the factor connecting the change in gravity to alcoholic strength.
The value of 'f' is not constant because the yield of alcohol is not
constant for all fermentations. In lower strength beers, more of the
'sugars' available for fermentation are consumed in yeast reproduction
than in producing alcohol. The table at 30.3, produced by the
Laboratory of the Government Chemist, shows the changing value of ‘f’
depending on the alcoholic strength of the beer.
*Use a suitably calibrated saccharometer adjusted for the temperature of the
representative sample.
30.3 Value of factor 'f' for various alcoholic
strengths
(OG - PG) % ABV Factor
Up to 6.9 Up to 0.8 0.125
7.0 – 10.4 0.8 – 1.3 0.126
10.5 – 17.2 1.3 – 2.1 0.127
17.3 – 26.1 2.2 – 3.3 0.128
26.2 – 36.0 3.3 – 4.6 0.129
36.1 – 46.5 4.6 – 6.0 0.130
46.6 – 57.1 6.0 – 7.5 0.131
57.2 – 67.9 7.5 – 9.0 0.132
68.0 – 78.8 9.0 – 10.5 0.133
78.9 – 89.7 10.5 – 12.0 0.134
89.8 – 100.7 12.0 – 13.6 0.135

Calculation of ABV when priming sugar is
added to beer
If you add priming sugar at the maturation stage to promote a secondary
fermentation and use the calculation method to ascertain the ABV of the finished
beer, you will need to make calculations based on the steps outlined below.
A barrel contains 163.6 litres which comprises 161.6 litres of beer which had an OG
of 1040 and 2 litres of added priming sugar with an OG of 1110. The final gravity of
the mixture after secondary fermentation is 1010.
Step Action
1. Calculate the ABV of the fermented beer using the formula:
(OG – PG) x f = a% ABV
where:
• OG is the original gravity of the beer
• PG is the present gravity of the beer (that is, final gravity after all
fermentation has ceased)
• a is the alcoholic strength, and
• f is the factor connecting the change of gravity to alcoholic
strength(1040 –1010) x 0.129 = 3.8
2. Calculate the ABV of the priming sugar using the same formula:
(1110 – 1010) x 0.135 = 13.5
3. Calculate the ABV of the contents of the container using the formula:
(Vb x Sb) + (Vp x Sp) = Sm
Vm
Where:
• Vb = volume of beer in the container
• Sb = ABV of the beer in the container
• Vp = volume of primings in the container
• Sp = ABV of primings in the container
• Sm = ABV of the container contents, and
• Vm = volume of container contents.
(161.6 x 3. + (2.0 x 13.5) = 3.9
63.6

[Beer O'Clock]

I use this -http://www.rooftopbrew.net/abv.php

[Wolfman]

I use this -http://www.rooftopbrew.net/abv.php

cheers for that mate..but 1 problem..my brew is in its last stages of fermentation (should be finished by tomorrow) and i took the temperature and put the details in and it said the ABV is 5.3%..but it smells quite a bit stronger than just 5.3%.

Wolfman

[Beer O'Clock]

..but it smells quite a bit stronger than just 5.3%.

Wolfman

What does 5.3% smell like ?

[Spud395]

Why bother with mathematics when your nose does the job?