What's going on in the bottle?

[tonight_we_fly]

Here’s a question. Feel free to argue.

Having seen varying different interpretations of this, my question is about whether the ABV increases at all during the secondary fermentation?

I always make bottle-fermented beer. I started off using kits and dextrose, adding half a teaspoon or so of the sugar to each bottle before filling and capping. As I moved on to extract brewing I progressed to using spraymalt instead, and nowadays I tend to stir about 300g (boiled for ten minutes in a small amount of water) in to the mix moments before I begin bottling. But my question is whether this has any effect on the final strength of the brew?

I’ve seen two different schools of thought on this subject. Some commentators suggest that the final addition makes no contribution to the alcohol content, and really just gives the yeast something to work on in order to carbonate the drink. However, elsewhere I’ve seen others suggest that the secondary fermentation process can add up to 0.5% to the final strength of the beer.

Frustratingly, I’m not really sure how to measure this for myself. Obviously a hydrometer can be used during the primary fermentation, but as this measures the gravity change before and after the fermentation process has happened, once I add the malt solution for bottling then obviously further malt has now been introduced to the mixture, and so I assume that any further readings taken after this point would become meaningless?

Would anybody have any comments?

 

[rpt]

You could take a reading just after you've primed the bottle and then again after a couple weeks. If it falls a couple of points then you have confirmed the 0.2% that I believe bottle carbonation adds.

If the yeast is producing CO2 then I would expect alcohol to be produced as there won't be very much oxygen available. It is during the anaerobic phase that yeast produces alcohol.

 

[calumscott]

Do the sums in beersmith. Normal ale priming rates give you 0.2%

I’ve seen two different schools of thought on this subject. Some commentators suggest that the final addition makes no contribution to the alcohol content, and really just gives the yeast something to work on in order to carbonate the drink.

It does give the yeast something to work on to carbonate the drink - they ferment it thereby producing CO2 and alcohol. The yeast (almost) exclusively in anaerobic metabolism in the bottle.

However, elsewhere I’ve seen others suggest that the secondary fermentation process can add up to 0.5% to the final strength of the beer.

Maybe at fizzy lager priming rates around 7 or 8g per litre you would get close to that. The 0.5% figure widely quoted comes from the instructions on the Coopers kits. It's just plain wrong...

You can calculate it. It's easier if you batch prime because you can measure it all. Take your FG before batch priming and calculate your ABV. Batch prime and take a new reading. Bottle and condition and pour a trial jar-full from the bottle and leave it a while to go flat and test again. Calculate the ABV of the second fermentation and add to the first for your final, in bottle, ABV.

For bottle priming you'll have to work out the total weight of sugar added to the brew and plug that into Beersmith or the like and use its estimation.

 

[tonight_we_fly]

Ah, thanks for the comments. Very useful remarks, and I'll try a pre/post priming set of measurements next time around to directly measure what happens, thanks!