Calculating OG and FG across a split fermentation?

[Moonraker]

Let's say I have a gallon of juice in a DJ, I have added sugar and measured the OG and add yeast. After 1 week of fermentation I split the gallon into two separate DJ's and add new juice that also has added sugar and that I have measured the OG before adding it.

How do I work out the overall OG - from adding the 2 original unfermented OG together and dividing by two, or the OG of the new juice plus the current gravity of the part-fermented juice and divide by two, or subtract the difference between the OG and current gravity on the part fermented juice and add it to the new OG - or some other combination?

Will I need to add extra yeast, or will the existing yeast simply use the sugar in the new juice to continue fermenting? How do I avoid having an overly sweet brew at the end - i.e adding more sugar than the yeast will be able to handle, is there an upper OG that shouldn't be exceeded that can be related to X kg of sugar added?

Or am I just overcomplicating this?

 

[johncrobinson]

The same yeast will be fine

I have answered this one before when discussing sugar feeding.
It`s TOTAL sugar into TOTAL volume,This calculation will give "effective" SG
FG is read by the hydrometer as normal

 

[Moonraker]

Thanks @johncrobinson I had a look through your postings trying to find your previous post, can you point me to it please?

Part 1 of my brew is 2 gallons of juice (1.040) with 500g sugar, and part 2 will be 1 gallon (1.045) with 250g sugar, so overall 3 gallons with 750g sugar - how do I work out the OG on that?

 

[LED_ZEP]

If I understand correctly you're adding 250g for every gallon (4.5l) @ o.g. 1.040. That would give a total gravity of 1.061

 

[Moonraker]

Thanks @LED_ZEP that's it. So can I infer from that that 250g per gallon equates to 0.020 (roughly)? So if I want an OG of 1.080 I need to add 500g sugar per gallon?

 

[LED_ZEP]

That's pretty much it. That's why you'll see 1kg / 4.5l for wow's with 3l of fruit juice 1000g plus about 300g for the sugar in the juice giving you an O.G. of about 1.100 (ish)

 

[johncrobinson]

Hi Moonraker, According to my calculations you will end up with three gallons of wine at 11.5% abv.

This is a modest strength table wine that should ferment dry without difficulty.

 

[johncrobinson]

As regarding a previous post,I think what I said was Don`t try to calculate but go by the hydrometer,
The question was how much sugar to add to supermarket fruit juice to arrive at a specific abv.
Somewhat different to your case.My bad,Sorry.

 

[Moonraker]

Hi Moonraker, According to my calculations you will end up with three gallons of wine at 11.5% abv.

This is a modest strength table wine that should ferment dry without difficulty.

Thanks, actually I'm going be trying to make blackberry cider, although it sounds as if I may end up with something that's neither fish nor fowl; 11.5% cider anyone? "Wider", "Cine"?

 

[LED_ZEP]

I make my cider 9.5 - 10%, there's no rules when you're in charge.