Calculating alcohol content after adding extra sugar

[Mork]

I decided to diverge from brewing beer in order to try out something called "Carrot Whiskey/Wine", which I'm sure many of you will be familiar with. I've been meaning to try it for at least 10 years, but haven't got round to it, mainly because the recipes say you need to mature it for about a year before drinking it, which is a long time (for me)! Anyway, I've finally started some. The recipe I'm following says to add half of the sugar initially, then after 6 days add the other half. So today is day 1 and I've just pitched the yeast. The starting gravity is 1080. So, my question is, when I add the remaining half of the sugar after six days, how do I calculate what the actual starting gravity is? Am I right in thinking that I simply take a reading before adding the remaining sugar, then take a second reading after adding it, then add the difference to the original gravity (1080) to give me the true "starting" gravity? Or is there some other formula?
I've used the recommended Lalvin EC-1118 yeast and pitched it at 25°C, which according to the information I've found online is slap-bang in the middle of the recommended temperature range of 20°C-30°C for this strain of yeast.
I welcome your thoughts and guidance please.

 

[LED_ZEP]

All you need to do is keep track of the weight of the sugar you are adding. I assume you know what total O.G. your heading for, so to work out how much total sugar you need use this formula in a spreadsheet. It will tell you in grams the total amount of sugar you need. for instance if you wanted a gravity of 1.100 in 23l that would be 6153g total sugar you'd need to end up adding. Substitute the values in red for gravity and volume.

If you know the starting gravity then just subtract that from the "OG" in the formula instead of subtracting 1 and it will tell you the amount of sugar left to add.

=SUM((("OG"-1)*2.675*"Vol in Litres")*1000)

 

[Mork]

All you need to do is keep track of the weight of the sugar you are adding. I assume you know what total O.G. your heading for, so to work out how much total sugar you need use this formula in a spreadsheet. It will tell you in grams the total amount of sugar you need. for instance if you wanted a gravity of 1.100 in 23l that would be 6153g total sugar you'd need to end up adding. Substitute the values in red for gravity and volume.

If you know the starting gravity then just subtract that from the "OG" in the formula instead of subtracting 1 and it will tell you the amount of sugar left to add.

=SUM((("OG"-1)*2.675*"Vol in Litres")*1000)

Thank you. I'm brewing two gallons and the recipe called for 4.4lb sugar (two bags) initially, then after 6 days another two bags.

 

[LED_ZEP]

Thank you. I'm brewing two gallons and the recipe called for 4.4lb sugar (two bags) initially, then after 6 days another two bags.

Is that US Gallons or Imperial Gallons? as they are not the same. If Imperial then you're looking at a total gravity of around 1.170 and that works out at around 22% - 22.5% ABV Which is going to be difficult to achieve even with EC1118

 

[DavidDetroit]

I ran into this when I added some fruit to a wheat beer. I took an OG and a FG with just the wheat beer. Then I used the FG as the OG and then added the fruit. It started fermenting again and when it was finished I took a FG. I just added the two numbers together. I don't know if it's accurate or not.
I did OG-FG (131.25) which was about 6%. The second reading was about 1.5% for an ABV of 7.5%.
I figured this out without reading how anyone else had done it so I don't actually know if it's accurate necessarily.

 

[Mork]

Imperial

 

[LED_ZEP]

@DavidDetroit

That would work, you can just keep adding up the "gravity points" difference every time you add more sugar to get a total gravity. i.e take a reading say 1.030 then add sugar and measure again now 1.060 so you've added 30 point to the starting gravity.

 

[DavidDetroit]

@DavidDetroit

That would work, you can just keep adding up the "gravity points" difference every time you add more sugar to get a total gravity. i.e take a reading say 1.030 then add sugar and measure again now 1.060 so you've added 30 point to the starting gravity.

Appreciate the response and good to know. My way (don't know any of the science that may exist on this) is intuitive but I had not researched. It only seemed like "common sense."