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i8humans 04-07-2011 03:55 AM

Low Attenuation
 
I've only just started brewing but I already need help on figuring out attenuation.

1st brew: APA, OG=1.051, single infusion @ 148F for 80 minutes, Wyeast 1056 smack pack, no starter, aeration via shaking, pitched at 72F and fermented at 64-71 for 10 days.

I checked the gravity after 4 days and it was 1.020 (61% attenuation). Still 1.020 after 10 days so I racked to secondary, waited 2 more weeks (still 1.020) and bottled.



2nd brew: APA, OG=1.067, single infusion @ 150F for 80 minutes, Wyeast 1056 smack pack, no starter, aeration via shaking, pitched at 72F and fermented at 67-72 for 10 days.

I checked the gravity after 4 days and it was 1.026 (61% attenuation). Still 1.026 after 10 days so I racked to secondary, waited 2 more weeks (still 1.026) and bottled.



3rd and 4th brews are not much different, 1.060 ==> 1.024 (60% attenuation), mashed @ 145F for 2 hours, except with these I used a 800ml starter, Wyeast 1728 (3rd brew), Wyeast 1056 (4th). With 3 and 4 I also used oxygen to aerate. The fermentation temp range on 3 and 4 was much more stable (70-72).




So I don't get the low attenuation. I mash low, oxygenate, different yeasts, starters, wait patiently, etc.

On all of these I use a calibrated refractometer, rouse the yeast after 7 days (no gravity change since day 4), etc.. They are all 2 gallon all grain batches. All of these recipes included 90%+ 2-row that was crushed by the supplier. Mash efficiencies all 65-75%. They start well, even requiring a blowoff, but stop after 3 days and don't finish.

Help! I don't want to make any more sweet tasting beer. Why do you think I'm stuck at 60% attenuation?

Buna_Bere 04-07-2011 01:51 PM

Are you plugging your FG readings into a spreadsheet, or calculator to adjust for alcohol content?
Did you take any hydrometer readings? I use a refractometer too, but only during the mash, and during the boil. I take hydrometer readings at OG into the fermenter, and FG, and I cool a preboil sample just to compare my hydrometer and refractometer readings. I find its much easier to get an accurate reading with the hydrometer. I got the 0-20 Brix refractometer so it would be easier to read, but I still find it difficult to read it more accurately than 0.5 Brix. Maybe you could degas one of your finished beers and get a hydrometer reading now?

Bob

jimsnewbrew 04-07-2011 02:24 PM

Here is a link to a refractometer calculator that takes the alcohol into account when testing a fermenting and or a finished beer.

http://www.northernbrewer.com/refractometer-calculator

i8humans 04-07-2011 09:23 PM

Thanks. I didn't know about the refractometer correction. The last 2 are still in the carboys so I'll check with a hydrometer. I had a hydrometer but replaced it with a refractometer which I assumed was the better tool.

An extra question for etbeer. You think I'd be better off fermenting on the highest end of the yeast recommendation and keeping it steady or letting it swing 5 degrees a little colder? I'm using 3 gallon glass carboy for the 2 gallon batch with no extra pressure. The starter was chilled in the fridge after fermentation then decanted and warmed back up to room temp on a stir plate.


Thanks again.


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