Alcohol Content / ABV

[RichieD]

Hi,
Question here about claimed ABV of kit brews. One example: I'm current brewing Bulldog Bad Cat Imperial Red. Claimed ABV is 7.5% on the box/packaging. Target starting Gravity from instructions is 1.061 and target Final Gravity will be 1008 - 1014. I am using my own excel database and the common formula of SG minus FG times 131.25 gives the ABV. Even using the target 1008 figure, using my formula this only produces a beer of 6.96% ABV. In reality FG may be higher than this, so the beer will be even weaker.
Another example: I made Brewferm Christmas Ale which is marketed to be 7.5%, but instructions say SG of 1.065 and FG of 1.010. This would produce, even with exact results, beer of 7.2% (much closer, admittedly). In reality my actual figures were 1.060 and 1.020, so my beer was a disappointing 5.25%. I know I may have just been unlucky here. I've noticed discrepancies in almost all the other brew kits I've used with all producing considerably weaker beers.
So the question is, is this anyone else's observations, and am I doing, or calculating something wrong?
thanks!

[wanus]

Hello Richie.Try your SG minus FG then multiply by 0.129.(Theory:If SG is 1.042 and FG is 1.010 42 minus 10 = 32.Then x by 0.129)I always brew under.For example if the tin says 23litre i always only brew 20litre.
Bewferms are excellent kits and you should do as it says on the tin but use candi sugar.Look online for other calculations for ABV.The one i mention if i remember was from John Palmers.

[IPA]

Your figures are not correct.

Try this formula
1061 minus 1008 =53 ÷ 7.36 = 7.2% (Wilf Newsom)

Or this one
1.061 minus 1.008 = 0.053 ÷ 0.0074 = 7.16% (Ken Shales)

[RichieD]

Hi Wanus and IPA, thanks v much for quick replies. I wasn't aware of these other formulae. IPA's seems to give a result closer to the target ABVs in the instructions. Wanus, your suggestion of using less water is a good one, thanks. In fact, I noticed with my latest brew (for 23 litres) that using 4 x 5 litre bottles of Tesco water (which I presume is dead accurate) came up to 23 litres on my pre-graduated fermenting bin, so I just left it at that. Target SG was correct, so hoping for a new strong brew.
Rich

[Nitro Jim]

I only ever make kits to about 19 or 20 litres. Obviously adding a hop tea increases the volume a bit but it just has to be done. I have never managed to get 40 bottles - but who cares, what I produce is drinkable!

[RichieD]

Think I might join you in that practise, Nitro

[Silver_Is_Money]

There are no math models that can reliably predict ABV from SG and FG over a broad range of values. All math models are merely approximations. They are not reality.

[guypettigrew]

I've always worked on the basis the ABV will be about 10% of the OG. In other words, a wort of OG 1.054 will yield a beer of about 5.4% alcohol, perhaps a bit less.

Guy

[RichieD]

Silver and Guy, thanks. In marketing terms, higher alcohol content will probably signify better value and 'better product' I would think, so it does not surprise me if the manufacturers put the highest possible ABV on their products given the possible variables, without telling outright porkies...Ultimately this will come down to "how smashed do I feel?" which can be affected by quite a affected by quite a few factors, eg how much you've eaten.
I really appreciate of your inputs. My conclusion is that kit beer probably ends up weaker than it says on the tin, so just make your own adjustments accordingly!