Does Vodka Lower FG Readings?

[rodwha]

I brewed a jalapeño cream ale that I soaked some sliced jalapeños in with 3-4 shots of vodka. I hit my OG spot on (1.054) and using US-05 the calculator suggested a FG of 1.013. Mine was 1.006.

This would make it a ~6.3% ABV beer instead of 5.4%, but it certainly doesn't come across as being this strong. I'm wondering if it gives a false gravity reading. I'm also curious if 3-4 shots of 40% ABV vodka alters the ABV of a 4 gal batch enough to adjust it more than 0.1-0.3% ABV?

 

[GuldTuborg]

Vodka will lower any beer's gravity reading (as it is less dense than water), but with the amount you added, I doubt it would be easily measurable with typical homebrewing equipment. That means, 3-4 shots of 1-1.5oz each is going to make a negligible difference. You just got higher than expected attenuation, which could have happened for any number of reasons.

I don't know if this is relevant or not, but I'm not sure what a "false gravity reading" is.

 

[HonestAbe]

I've had a false gravity reading prior to pitching. I was doing an extract kit and added top off water then dropped in the hydrometer. I was off on my OG by 25 points. I scratched my head aerated the wort getting ready to pitch and took one more reading that was spot on. Simply pouring in the top off water did not force it to mix well and messed up my gravity reading.

 

[thadass]

It would lower the gravity, yes. Vodka is ~0.950 SG, and GU=(SG-1)*1000, so:

512oz (4 gallons) beer at 1.006 = 6GU*512oz = 3072 GUoz
6oz (4 'normal' shots) vodka at 0.950 = -50GU*6oz = -300 GUoz

(3072-300)/(512+6)=2772GUoz/518oz = ~5.4GU, or approx 1.0054. Adding 4 shots of vodka would drop a little more than half a gravity point.


for the ABV alteration, it would be (512oz*5.4%)+(6oz*40%)/518oz = 27.648+2.4/518 = 5.8%

 

[GuldTuborg]

I've had a false gravity reading prior to pitching.

While I certainly wouldn't call that a false reading, I suppose that's a matter for another thread. Your point is well taken, though: when adding water to a partial boil extract recipe, you must stir until your arms fall off.

 

[HonestAbe]

I know that now! However it was a pretty disappointing 15 minutes before I figured out the error