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?