Calculating ABV after adding Agave Nectar to Secondary

[rthiessen]

Hello,

I have brewed a Belgian Pale Ale and the OG was 1.048. This was a 5 gallon batch and I split it into two 2.5 gallon fermenters. During secondary in Fermenter #1, I added 11 oz of agave nectar and days later the gravity reading was 1.012. Then I added another 8 oz of Agave Nectar and now the gravity reading is 1.010. What is the easiest way to calculate the ABV of this 2.5 gallon Belgian Pale Ale?

Thanks!
Rob

 

[Lefou]

First off, you need to find out the specific gravity of your agave nectar to be sure. The serving amount on the label should provide sugar content per serving and that will allow you to calculate sugar/weight.
You already know your original gravity and volume of Pale Ale - 1.048 and 2.5gal. Just add the total weight of agave nectar to your fermentables. The gravity of the source brew will still be 1.048 regardless of volume.

Brewer's Friend lists generic agave nectar as contributing 52.5 points/gallon(10.5 points per lb.), so 19oz. gives about 12.5 gravity points. Added to 1.048, gives you an estimated total OG of about 1.061. Depending on your yeast's attenuation and your mash method, you could get about 6% ABV from the batch in Fermentor #1 supplemented with agave.

 

[Lefou]

Expect a slightly dry and mildly alcoholic result from the agave. It will ferment out much like honey and may require a bit of extra time to "clean up" any yeast metabolism byproducts from fermentation.

I regularly make "dry" bottle-carbed ales and lager in the 1.040-1.050 range and get a slight green fruit or apple aroma (acetaldehyde) as my beer carbonates over a period of 3-4 weeks. You may notice it too. If the gravity of your beer exceeds this range it may need more time to reduce the fruitiness the extra gravity will contribute.