ABV Lower than expected by ~2%...

[adiochiro3]

A friend and I bottled Kilkenny Irish Ale on Sunday, and the alcohol production was at 4.8% when the expected should be ~7%.

The Recipe:

9 lbs. Pale LME
1 lb. 10-13° L. Crystal Malt –crushed
Perle, Northern Brewer, Fuggle, & East Ken Golding in a multi-pak (weight varies depending on alpha acid content)
Irish Moss pre-mixed with bittering hops
14 grams Yeast Lab Australian Dry Yeast (1 packet) or Liquid yeast 1084 XL

We fermented in primary 2 weeks at an average temperature of probably 65 degrees F.

We followed the LHBS instructions, except for one thing: I believe I added too much water (~ 0.5 gal.) right before pitching the yeast, which -- if ABV is just strictly a function of dilution -- should have meant we would have had a 5.3% ABV if I had not added too much water -- all else being equal.

We have 3 questions:

1) Is ABV a straight dilution ratio in this situation, or did the extra ~10% water volume affect our fermentation in other ways?

2) Did our slightly low fermentation temp lead to incomplete fermentation in that 2 week period? 3) And if so, did we create bottle bombs by adding a standard amount of priming sugar on top of un-fermented sugars?

I don't really care about the actual alcohol level except as it pertains to getting appropriate results.

Thanks!

James

 

[eastoak]

did you get and original gravity reading to compare with the final gravity?

 

[beergolf]

how are you measuring ABV?

Did you get a OG and a FG? If so the calculation is (OG - FG) X. 131.25= ABV.

If you are reading it on the hydrometer then you are using the wrong scale.

With 9 lbs of a extract you should get about 6.8% abv .ading an extra 1/2 gallon of water will reduce it to about 6.1%

 

[adiochiro3]

did you get and original gravity reading to compare with the final gravity?

Yes. OG: 1.056 @ 70F; FG: 1.020 @ 65F

 

[beergolf]

Yes. OG: 1.056; FG: 1.020 @ 65F

Was it a partial boil with top off water?

If so then your OG measurement probably was off. It is almost impossible to miss your OG with extract.

 

[adiochiro3]

Was it a partial boil with top off water?

If so then your OG measurement probably was off. It is almost impossible to miss your OG with extract.

Yes, it was a partial boil with top off. I believe I topped off with ~0.5 gal. too much water as I wound up with about 5.5 gal. finished beer. I thought missing an OG with extract would be strange, which is why I thought incomplete fermentation was a possibility.

What would cause my OG measurement to be off? I've used hydrometers in chem labs, The wort was at 70F when I measured, and I had my reading glasses on D)....

 

[adiochiro3]

how are you measuring ABV?

Did you get a OG and a FG? If so the calculation is (OG - FG) X. 131.25= ABV.

If you are reading it on the hydrometer then you are using the wrong scale.

With 9 lbs of a extract you should get about 6.8% abv .ading an extra 1/2 gallon of water will reduce it to about 6.1%

I'm not sure where else would I take my reading. Only one scale is obvious on my hydrometer. I plugged my OG & FG into an online calculator to get my ABV.

Thanks for the formula!

 

[mike_in_ak]

I second your initial reading being low. That wouldn't add up with the amount of LME you added. You're probably up around 7%.

Someone who is less lazy than I should put it in beer smith.

Edit: didn't see someone already calculated it at 6.8. Add whatever the crystal does and there you have it.

 

[mike_in_ak]

Check calibration on your hydrometer?

 

[adiochiro3]

I second your initial reading being low. That wouldn't add up with the amount of LME you added. You're probably up around 7%.

Someone who is less lazy than I should put it in beer smith.

LOL! What would throw my OG reading off?

 

[mike_in_ak]

Check calibration on your hydrometer?

This?

 

[mike_in_ak]

LOL! What would throw my OG reading off?

Also lots of people lately have been talking about stratification. The water and wort stratify based on temp and density, I guess until the yeast mix everything up. So you may have just taken a non-representative sample.

 

[iaefebs]

LOL! What would throw my OG reading off?

stratification

 

[adiochiro3]

Check calibration on your hydrometer?

I assume that's done in plain water?

 

[mike_in_ak]

Yeah. Supposed to read 1.0 (although my water does not (gross)).

The paper slip gets moved, etc.

Also, just search the forum for stratification. It's been talked about in probably three different treads over the past month, so it seems like it's definitely a thing.

 

[mike_in_ak]

And of course the water to calibrate has to be at the correct temp, which I think for mine is. 60 *f.

 

[adiochiro3]

So my hydrometer calibration is off: in water @ 60F it reads 1.005.

 

[mike_in_ak]

You water may have other solutes. That's a pretty low margin. Before you through it away try distilled water.

 

[adiochiro3]

You water may have other solutes. That's a pretty low margin. Before you through it away try distilled water.

That's my next move. Thanks everyone!