Extreme attenuation, high ABV

Hello,

I recently bottled my latest batch and was somewhat confused by the numbers from my pre-bottling readings. The recipe instructions said that I should expect a brew with an ABV of just over 4% (Northern Brewer's Biere de Table), but my OG was 1.051 and FG was 1.008, for an ABV of 5.6% and attenuation over 84%, way higher than the ~75%, which I expected. The temperature for both readings was ~65 degrees F. Is this weird somehow? I always work with liquid yeast and a starter, no matter what the gravity. Would this have something to do with it?

Also, I cold-crashed the beer inadvertently. I had turned off the heat in my apartment before leaving for the weekend and came back to a room temperature of ~52 degrees F. The fermentation had been over for about a week at that time, so I'm not worried about that, but half of the water in the airlock had disappeared out. Is this weird somehow?

Thanks!

According to NB, your OG should have been about 1.043. Assuming that you used an extract kit, it is unlikely that your OG was actually much above this (unless you used too little water). Did you top off with water after a partial boil? More likely than not, your wort and the water weren't fully integrated when the sample got drawn, leading to an inaccurate hydrometer sample. If that's the case, your attenuation is actually more like 81%, and your final ABV 4.6%. In either case, attenuation in the 80%-85% range isn't terribly high for belgian/french farmhouse strains, though I haven't used Wyeast 3725 so I can't speak from experience. Having a starter wouldn't cause any problems.

When temperature drops, the volume of the gas in your carboy's headspace contracts, creating a small vacuum. This can often suck liquid from your hydrometer into your beer. Use normally diluted starsan or vodka and it's no problem.

Thanks so much for that quick and enlightening response! I didn't add any more water after the partial boil, which seems to be the culprit here. In the future, I'll use the OG posted on the recipe kit and just take a final before bottling to make sure that fermentation is over and to get my ABV reading.

Also, thank you for the explanation of the disappearing water. I did use diluted StarSan in the airlock, so I'm not worried about contamination, but it's nice to know what happened.

Bartmannj said:

Thanks so much for that quick and enlightening response! I didn't add any more water after the partial boil, which seems to be the culprit here. In the future, I'll use the OG posted on the recipe kit and just take a final before bottling to make sure that fermentation is over and to get my ABV reading.

Also, thank you for the explanation of the disappearing water. I did use diluted StarSan in the airlock, so I'm not worried about contamination, but it's nice to know what happened.

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That would certainly explain the high OG. You basically brewed a 5 gallon batch as 4 gallons (or however much you ended up with). That's totally fine, and will make it a more "standard" Biere de garde recipe than the table version that this kit describes. I'm sure it will be great! For future, though, if you want to end up with the beer described in a recipe you have to make sure that you end up with the right amount of liquid at the end. As long as you're with extract, you don't really need to worry about much else beyond final volume.

If you are looking to find an easy way to measure volume, just get a gallon jug. Fill up your fermentor to 5 gallons and mark it with a sharpie.

I marked my carboy at what seemed like the 5-gallon mark, but I eyeballed it based on the water volume in my bottling bucket. That would explain why my past batches had skewed gravity readings. The gallon jug way will be a lot more accurate...and I already swiped a Sharpie from my office to mark the fermenter at home.

Thank you again. I really appreciate the help.