Will adding alcohol throw FG readings off?

I searched, but most of the results I uncovered were for adding fruits, or honey into secondary, and the resulting change in S.G.

I'm brewing a stout, and added vanilla & Jameson into the mixture when racking to secondary. I don't have my notebook with me, but I know my S.G. at the transfer to secondary was ~ 1.010. After adding 2 cups of whiskey, with the alcohol still in it (read, not boiled off), will my FG readings before bottling still be accurate? In other words, will (OG - FG) x 131 still give me an approximate ABV%, or will the added alcohol somehow alter the reading?

My gut's telling me I'm just overthinking it, and normal readings will be fine, but I'm relatively new to this, so I'm just looking for some reassurance.

Thanks.

The normal readings will be fine for your purposes. This isn't an exact science after all.

However, technically the added alcohol will affect the FG readings. Even the alcohol produced by the yeast affects the FG. The OG is based off of the amount of sugars dissolved in water. The FG is not, however, just the remaining unfermented sugars that are still dissolved in the wort. It also contains alcohol which has a lower SG than water. This combination will give you a lower FG reading than if the alcohol weren't present.

In the end, however, know that as homebrewers we are just looking for an estimate of the amount of alcohol present and the readings you get are fine for that purpose.

Yes. Anything added will serve to dilute the mixture. It's no different than adding water with respect to SG except that, instead, you are adding something already fermented.

On another token, adding too much alcohol to the brewer can effect SG readings too.

Is your beer done fermenting?

Cause if it is, what's the point in taking another gravity reading?

To find the ABV(Alcohol by Volume) just calculate how much, Alcohol there is in your volume.

Your question was: "will (OG - FG) x 131 still give me an approximate ABV%". The answer is "yes". The final gravity will be lower than it would have been had you not added alcohol, but the equation holds.

GilaMinumBeer said:

Yes. Anything added will serve to dilute the mixture. It's no different than adding water with respect to SG except that, instead, you are adding something already fermented.

On another token, adding too much alcohol to the brewer can effect SG readings too.

Click to expand...

So if something like honey or maple syrup(think that qualifies as anything) is added it will dilute the mixture? What about adding other beer to your beer? If I fill half a glass with Bass and measure the gravity, then fill the rest with Guinness and measure again, it won't change?

It's no different then adding water? Water has an SG of 1! Your beer does not, neither does whiskey.

If you beer is done, which it appears to be at 1.010. You can find the ABV of your beer by using (OG - FG) x 131.

When you add your whiskey you will change your gravity, but don't use that to calculate your ABV.

Let's say your brew is 5% ABV and you made 5 gallons.

Your brew has .25 gallons of alcohol if you were to separate it:

5 gallons * .05 = .25 gallons of alcohol

If you add 2 cups of 100 proof whiskey:

2 cups * .5 = 1 cup alcohol = .0625 gallons of alcohol

Now divide your total alcohol by total volume,

(.25 + .0625 gallons) / (5 gallons + .125 gallons) = .06 or 6.1% ABV

Think I got that right.

ongreystreet said:

If you beer is done, which it appears to be at 1.010. You can find the ABV of your beer by using (OG - FG) x 131.

When you add your whiskey you will change your gravity, but don't use that to calculate your ABV.

Let's say your brew is 5% ABV and you made 5 gallons.

Your brew has .25 gallons of alcohol if you were to separate it:

5 gallons * .05 = .25 gallons of alcohol

If you add 2 cups of 100 proof whiskey:

2 cups * .5 = 1 cup alcohol = .0625 gallons of alcohol

Now divide your total alcohol by total volume,

(.25 + .0625 gallons) / (5 gallons + .125 gallons) = .06 or 6.1% ABV

Think I got that right.

Click to expand...

Thanks. This is what I'm looking for.