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Calculating ABV across multiple fermentations - how?

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muppix

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A (hopefully) quick question for the seasoned cider makers: how can I calculate ABV across successive fermentations? For example -
  • Day 01: pressed a bunch of apple juice, OG = 1.045
  • Day 30: SG now at 1.007, so ABV more or less 5%. Racked to new FV and add sugar, SG rises to 1.036.
  • Day 60: FG at 1.005, fermentation stopped, shove it in a bottle.
But what's the final ABV? Did we gain 5% from day 1 to day 30 (1.045 to 1.007) and another 4.07% from day 30 to day 60 (1.036 to 1.005) making a total of 9.07% Have I made a schoolboy error in assuming that adding sugar on day 30 doesn't knock the ABV down again? What if the yeast that I'm using - just natural apple in this case - tops out at a certain point, say 8%. Will my cider at day 60 be sweet and refuse to go below a certain FG unless I add more / different yeast?

Sorry about the barrage of questions there, hopefully I've asked them in a coherent manner. The example above is fictional but relates roughly to a batch that I'm working on now. I've bottled half of it at the end of primary with absolutely nothing added except for some priming sugar and a little Xylitol, the other half has been racked into fresh demijohns and I'm hoping to do something special, maybe see how high I can push the ABV, try some flavouring, whatever. It's a fantastic base and I won't get another until next year's harvest, so I want to make sure I do it right.

Thanks for your help!
 

simon12

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But what's the final ABV? Did we gain 5% from day 1 to day 30 (1.045 to 1.007) and another 4.07% from day 30 to day 60 (1.036 to 1.005) making a total of 9.07%
I think its a yes there could be a very tiny adjustment for the alcohol content throwing it off slightly but unless you need the exact amount for HMRC its close enough.
 

muppix

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Cheers simon12 - no HMRC involved (thankfully) but it's good to know I can add the ABV derived from successive fermentations.

The question now is how do I know I've topped out, is it when the FG refuses to drop below a certain level, even though it's been lower on previous fermentations? In other words, if it dropped to 1.007 on day 30 and then I added more sugar, but now I can't get it to go below 1.013, does that mean my yeast has stopped working at 8% ABV?

I'm keen to play around a bit with what's left of my batch but I don't accidentally want to make it too sweet.
 

simon12

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Cheers simon12 - no HMRC involved (thankfully) but it's good to know I can add the ABV derived from successive fermentations.

The question now is how do I know I've topped out, is it when the FG refuses to drop below a certain level, even though it's been lower on previous fermentations? In other words, if it dropped to 1.007 on day 30 and then I added more sugar, but now I can't get it to go below 1.013, does that mean my yeast has stopped working at 8% ABV?

I'm keen to play around a bit with what's left of my batch but I don't accidentally want to make it too sweet.
I think the answer is yes again. I am not a cider guy but I think cider yeast should be good for at least 8%+ and don't take what I said as gospel hopefully some else can confirm or dent what I said.
 

johncrobinson

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From a lot of responses and i confine myself to the wine on this forum as the beer brewers could leave me dead in the water.
However don't stress over the final gravity it all depends on what you made the brew from in the first place.
if you have lots of organic matter you are never going to get extremely low fg.
 
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