Alcohol % Added By Secondary Fermentation

[Goofinder]

I like to have a fairly good idea of the ABV% of my beers, and the numbers I come up with seem to 'match' well enough with commercial beers based on on-going experimental evidence :chug:

But now that I'm brewing different styles that have different carbonation levels the amount of priming sugar changes a bit from batch to batch, so I'm wondering how much of an effect this has.

So far, I've been using the ABV% based on the OG and FG (can't remember the exact equations, but it involves converting to deg Plato and comes up with the same numbers as BeerSmith does) and then adding 0.5% for priming for all batches. I found this number ages ago, but have also seen references to 0.2% and 0.4%.

So, for the bottlers out there, what method do you use? Do you even care? Should I care? Is there so much error in the ABV% calculation from OG and FG readings that it's not going to matter? Should I attempt to work out the contribution based on the amount of priming sugar used and its fermentability?

Also, before anyone suggests it, a keg system is currently in the planning stages and should be pouring in the next couple of months.

 

[sponge]

I always went on ummm 0.3% i think (computer crashed, lost all my notes, so not completely sure)

And when I get back into brewing again I'm just going to stick with 0.3% even if its not correct (unless someone would like to correct me then I am more then happy to change the value)

As can be seen, im not worried at the exact numbers. They're all too smaller percentages for me to worry all that much IMHO


Sponge

 

[buttersd70]

Not that you really need to be that specific, you can work it out if you want.

If you want to work it out there are a couple of ways. Method 1 involves taking a refractometer reading of the bottled beer, simmering a sample over a period of time to remove the alcohol, then topping it up to the original volume once cooled with distilled water. Then the difference in gravity out of the bottle, and gravity of the dealcoholised sample can be compared, to work out how much alcohol was removed....awkward, time consuming and a pita.

Method 2 is the one I use. Assuming that you prime with dextrose....you have the OG and the FG already, which has given you your abv prior to bottling. Go back to the recipe itself, and add dextrose to it in the same per litre amount as what was used for priming, for the full batch volume. So you disregard any losses from transferring to secondary, etc. This will give you a new OG to work with (which is what you would have gotten if you had primed the whole batch at the start of fermentation, instead of at the end of frmentation, if you see what I mean), substitute this into the formula for abv, leaving the fg as-is, and bingo, it will give you the ABV post bottling. Of course, there is error in this, because the priming sugar wouldn't have fermented 100% absolutely, but it will be close enough, particularly for carbonation levels that aren't "average", where the "0.5%" generalisation doesn't work.

 

[Adamt]

Just add your priming addition to your ingredients list in Beersmith/Promash/whatever, it will work it out for you.

 

[buttersd70]

Just add your priming addition to your ingredients list in Beersmith/Promash/whatever, it will work it out for you.

Which is what I was trying to say in a roundabout, fannying about, failing to get to the point, backwards, forwards, complicated way. :lol:

I should change my username to Inspector Grimm.

 

[Insight]

Not that you really need to be that specific, you can work it out if you want.

If you want to work it out there are a couple of ways. Method 1 involves taking a refractometer reading of the bottled beer, simmering a sample over a period of time to remove the alcohol, then topping it up to the original volume once cooled with distilled water. Then the difference in gravity out of the bottle, and gravity of the dealcoholised sample can be compared, to work out how much alcohol was removed....awkward, time consuming and a pita.

Method 2 is the one I use. Assuming that you prime with dextrose....you have the OG and the FG already, which has given you your abv prior to bottling. Go back to the recipe itself, and add dextrose to it in the same per litre amount as what was used for priming, for the full batch volume. So you disregard any losses from transferring to secondary, etc. This will give you a new OG to work with (which is what you would have gotten if you had primed the whole batch at the start of fermentation, instead of at the end of frmentation, if you see what I mean), substitute this into the formula for abv, leaving the fg as-is, and bingo, it will give you the ABV post bottling. Of course, there is error in this, because the priming sugar wouldn't have fermented 100% absolutely, but it will be close enough, particularly for carbonation levels that aren't "average", where the "0.5%" generalisation doesn't work.

Just tried method 2 on a beer carbonated to 2.4 volumes (pretty average) and the result was a gain of roughly 0.4%.

Butters, why do you think that less than 100% of the priming sugar will ferment?

 

[Goofinder]

Thanks... for both the long and short replies

 

[buttersd70]

Butters, why do you think that less than 100% of the priming sugar will ferment?

There are a couple of reasons. Dex isn't anhydrous, which means that it has water molecules in its chemical structure. The other is that yeast can only ferment so far. In a perfect world, it would ferment anhydrous simple sugars to 100%, but we don't live in a perfect world. Dex varies in its fermentability somewhere in the region of 95-97%, from memory, and that is assuming full attenuation. The other consideration is a time frame issue. Even if the prime was consumed totally, the yeast would continue to work on more complex sugars left in the wort, so given enough time, the carbonation levels would change anyway.

But such considerations are minor, and given the scale of error just from hydrometer readings amongst other things, aren't even really worth considering. but seeing as how you asked.... :lol: