Alcohol Content

[JohnH]

next question.......i have 2 books- one by rodgers-wilson and one by laurie strachan.
both aussie books.
one says divide the difference in the sg readings by 7.6.............so a difference of 38 would give you 5% alcohol
the other (rodgers-wilson) doesn't actually give a calc but in all the recipes it gives start and finish sg's and alcohol content ........and that calc is running at way less than 7.6....for a difference of 38 it says 5.8%......so that's about 6.6...........

who is right................


and while I'm at it, strachan says keep your beer very cool once bottled an d rodgers-wilson says 'warm place'......no wonder a bloke drinks!

 

[bum]

Does the second calculation allow for bottle conditioning? From memory the 7.6 one does not. Does this make up for the shortfall in the results you're seeing?

I think that you end up with what can best be considered an educated guess regardless of what formula you use anyway.

 

[ivanhoe]

A few equations here if you are interested.

http://en.wikipedia.org/wiki/Gravity_(alcoholic_beverage)

 

[JohnH]

Does the second calculation allow for bottle conditioning? From memory the 7.6 one does not. Does this make up for the shortfall in the results you're seeing?

I think that you end up with what can best be considered an educated guess regardless of what formula you use anyway.

you might be right; i can't find reference in the books now but i do remember reading it...........didn't think it added such a high % to the content..but it might be right;
agree- it's all a bit hit and mis- i won't be relying on sg readings & calcs when deciding whether to drive!

 

[Synthetase]

After bottling, you need to keep the bottles in a warm place for a couple of weeks for the priming sugar to ferment in the bottle allowing carbonation. Once carbonation is finished, the bottles should be stored as cool as possible to maintain stability. If you're going to drink your beer within a few months this isn't really an issue (I keep my bottles at room temperature because I can't fit them all in the fridge , it's mainly to allow for storage over long periods of time.

 

[bullfrog]

I just use the chart on the Country Brewer website, and then add 0.5% because I bottle prime.

(The chart, in PDF version, is in the Handy Hints section of the Country Brewer website, if anyone wants something [rough as it may be] to print off and have handy in their brewing room. Not sure how accurate it is, but I use it all the time.)

 

[MHB]

Ok now you have me thinking, I have always used Change/7.64 interesting to work it through and see what we get just for fun.
Say a brew (22.5 L) goes from 1.050 to 1.010 a change of forty points, the start and finish masses are (22.5 x 1.05 and 22.5 x 1.01) 23.625Kg and 22.725Kg or a change of 0.9 Kg.
Say the only way we can lose mass is as CO₂ and as we make 1 Mole of Alcohol for every Mole of CO₂ and as Number of Moles = Mass (g)/Formula Weight and CO₂ has a FWT of 44 and Alcohol (eth) has a FWT of 46.1
Number Moles CO₂ = 900/44 = 20.455 therefore Mass alcohol is Moles (20.455) x FWT (46.1) = 942.955g or 0.942955 Kg
%ABW is 0.942955/ 22.725 = 4.19%
Ethanol has a density of 0.785 so going back to the 0.942955 Kg we made gives us V = 0.942955/0.785 or 1.2 L of Ethanol
%ABV = 1.2/22.5 x 100 or 5.33 %

Back to the original question

A change of 40 points divided by 7.5 gives 5.33333%, 7.64 gives 5.23%, neither allows for bottle conditioning.

Really wouldn't matter, given the measurement errors and limitations I don't think you would put a lot of faith in that second decimal. There are also a shed load of other factors like yeast reproducing and taking out mass, dissolved Oxygen and cold break material coming back into solution (or some of it after the yeast chews on it a bit), up to 30 % of the Iso-Alpha can stick to yeast and be carried out of solution, so maybe that first decimal is a bit shaky to.

Think I will just keep using the 7.64 number its close enough.

MHB

 

[ianh]

If you look at the formula in my spreadsheet it shows how to calculate it.

Its based on data from UK gov for determination of excise on beer, cannot find the site I got it from.

The factor varies from 128 to 133 based on the OG of the wort.

For practical purposes a factor of 131 is the best for homebrew, this is a multiplication factor using division the factor is 7.634

For bottling I calculated and addition of 0.4% alcohol for sugar using the scoop.

For bulk priming you need the weight of sugar/dextrose times a factor 406/386 times 131 divided by the volume.

cheers

Ian

 

[wabster]

I use the Alc calculator on the Cascade home brew website http://www.cascadehomebrew.com.au/brewkits/calculators.asp and I just put the OG 1050 FG 1010 in an get 5.7%. I wonder if a figure of .5% for priming is built in?

The calc above, dividing 40 point diff by 7.634 gives 5.24

Is that a significant difference? 0.46% in dealing with such a figure.

Not for me personally but I'm sure it does for some folks.

 

[casualties_army40]

hey way i calculate it is OG-FG/7.46 + 0.5 (for bottling) = ABV

thats how it says to do it in the coopers can instructions.

 

[booyablack]

I use the Alc calculator on the Cascade home brew website http://www.cascadehomebrew.com.au/brewkits/calculators.asp and I just put the OG 1050 FG 1010 in an get 5.7%. I wonder if a figure of .5% for priming is built in?

The calc above, dividing 40 point diff by 7.634 gives 5.24

Is that a significant difference? 0.46% in dealing with such a figure.

Not for me personally but I'm sure it does for some folks.

Wabster,

I use that cascade calculator too, because all you have to do is punch in the figures and it bangs out a percentage. To answer your question, yes, the Cascade calculator DOES add 0.5% to account for bottle priming.

 

[RobboMC]

After bottling, you need to keep the bottles in a warm place for a couple of weeks for the priming sugar to ferment in the bottle allowing carbonation. Once carbonation is finished, the bottles should be stored as cool as possible to maintain stability. If you're going to drink your beer within a few months this isn't really an issue (I keep my bottles at room temperature because I can't fit them all in the fridge , it's mainly to allow for storage over long periods of time.

Ah the old 'warm place' thing.

When I got to think I was a half decent brewer I had a comp judge taste my beer and score it. What I got back was devestating, basically scolded for brewing above 20 deg C. But I had religiously been brewing at 18-19 deg C for many months.

I had been placing my bottles, as the instructions say, in a 'warm place'. Now the warmest place I have is a nice little upstairs storeroom that faces West and probably gets to 40 deg in summer. Banana esters were less than 10% of the alcohols, but there was enough for an experienced judge to slam the result. 'Warm place' means not in the fridge, and not outside in the garage if you live at the North Pole. It doesn't mean 35 deg C.

I now do my carbonation at controlled brewing temperature and my following judgements have proved to be much more favourable.
Many will say the carbonation temp doesn't make that much difference, but my experience showed that it does.

 

[JohnH]

thanks for all the replies- comprehensible and otherwise........

cheers