Yeast Starter and ABV Calculations

[KWright_VT]

So I made my first yeast starter this weekend with 1/2 lb DME in 1.8 liters of water. Pitched the whole flask into 5 gallons of RIS with an OG of 1.102. After pitching, my OG was 1.092, but I already had alcohol in the starter. So how does one go about calculating the ABV of the beer?

The 1.102 was obviously thinned by the roughly 1.040 OG of the starter, so should I calculate what the theoretical OG would have been if I added the 1.8 liters of starter wort to the 1.102 stout?

 

[KWright_VT]

Just did a little calculation:

5 gallons of 1.102 wort, plus 0.48 gallons of 1.040 wort

(1.102*5+1.040*.48)/5.48 total gallons = 1.097 theoretical OG

If my thinking is right, I can use this to calculate FG once I get there.

Next time, I will decant so this isn't so tough.

 

[slym2none]

*redacted*

You got it.

 

[KWright_VT]

Thanks, the math geek in me had to work it through, but wanted to check. It looks like she'll be a pretty good one, my first big beer.