Correct Alcohol Formula

[Helium]

Hello,

This is my first post, based on the fact that I'm in the middle of my first brew.
It's an amber kit from beer-wine.com, whose warehouse is near where I live.
They're cool, and give loads of free advice.
Anyway, so their instructions have my starting gravity at 1.040, and finished at 1.012-1.008.
Now I've seen a formula that is SG-FGx131 to get alcohol content, and then I've seen like 4 others.
Which is correct?
Also, why would my hydrometer scale have lower alcohol with a lower gravity? i.e., if I get to 1.008, the alc. level on that line is 2%.

Thanks.

[Mill Rat]

Originally posted by Helium
Hello,

This is my first post, based on the fact that I'm in the middle of my first brew.
It's an amber kit from beer-wine.com, whose warehouse is near where I live.
They're cool, and give loads of free advice.
Anyway, so their instructions have my starting gravity at 1.040, and finished at 1.012-1.008.
Now I've seen a formula that is SG-FGx131 to get alcohol content, and then I've seen like 4 others.
Which is correct?
Also, why would my hydrometer scale have lower alcohol with a lower gravity? i.e., if I get to 1.008, the alc. level on that line is 2%.

Thanks.

Check your formulas. I think you've found formulas for both % alcohol by volume (ABV) and % alcohol by weight (ABW). They're not the same, and you'll find ABV used more often, I think because the higher number looks more impressive.

The scale on your hydrometer is potential alcohol, the ABV you would reach if the sugar required to float the hydrometer at that level all fermented out. The less sugar, the lower the hydrometer floats, and the less sugar available for the yeast to make alcohol with, so the low potential alcohol. You can get a rough idea of your beer's ABV by subtracting your beer's final potential alcohol from your wort's potential alcohol. This number will a little higher than the actual ABV because the water-alcohol mix in the beer is less dense than the water in the wort and will make the hydrometer flaot a little lower. Maybe someone else has a conversion formula handy.

[Trogger]

That is a triple scale hydrometer. The alcohol % you are read is the alcohol potential. That means if you take the “alcohol % reading” when you start, and the “alcohol % reading” when you finish, then subtract the end from the beginning, that gives you how much alcohol is in there. In my opinion, that isn’t as accurate as taking the gravity reading and putting it into the correct calculation. For that, I’ll defer to someone else as I’m at work and don’t have my formulas here. At home, I have it built into a spread sheet. I input the OG and FG and it gives me the ABV. Also, read the instructions on your hydrometer, it will give show you how to adjust for different temperatures. They are only perfectly accurate at a certain temp. I believe that is 60 degrees, for most models.
Congrats on your first brew, good luck, and keep at it!

[Helium]

Thanks for the tips.
I've read the bit about temperature and proper calibration, but the variance from say 60* to 76* is in the hundreths, .003, not something to be too worried about.

This one brew is driving me mental. It was very warm out when I did the primary, and the foam had died down after 2 days, and my gravity dropped by half, to 1.020 as my instructions said it should. So I siphoned into my glass carboy on 8/15, and checked it twice since, for a taste and to check the gravity. The first taste was good, very malty, the second tasted more like tea, which really freaked me out, and when I checked the gravity, it was still only 1.016. That was on 8/22. I was hoping to have people over to drink it on 9/2, but I don't think it's enough time to carbonate/age correctly.

[brewmonkey]

I would check those variances again as that does not sound right as well .003 is almost 1plato which is a rather large variance IMHO.

However, welcome to the board.

[Helium]

Hmmmm. OK, well if 1 plato is .003, and 1 plato is a lot, then maybe I'm screwed! :)

[Mill Rat]

Originally posted by Helium
Hmmmm. OK, well if 1 plato is .003, and 1 plato is a lot, then maybe I'm screwed! :)
You're not screwed, you may just have to postpone the event. You are right to let the beer determine the schedule. If it's not ready, it's not ready, and no mean looks at the carboy while vigorously pointing at the calendar will get the yeast to hurry up. And it will still be the best beer you've tasted. Patience is difficult at this stage, so occupy yourself in the meantime by brewing the next one.