I have brewed 3 all-grain batches now that have a high final gravity:
Imperial IPA: Target OG - 1.079, Target FG - 1.011, Actual OG - 1.070, Actual FG - 1.020, Yeast - US-05. Common attenuation range seems to be 73% - 78%. Apparent Attenuation: 70%
American Pale Wheat Ale: Target OG - 1.064, Target FG - 1.018, Actual OG - 1.054, Actual FG - 1.022, Yeast - White Labs WLP051. Advertised attenuation range: 75% - 80% Apparent Attenuation: 58%
Belgian IPA: Target OG - 1.060, Target FG - 1.014, Actual OG - 1.061, Actual FG - 1.027, Yeast - White Labs WLP500. Advertised attenuation range: 70% - 75% . Apparent Attenuation: 54%
I brew with Chicago water which has a high ph (around 8), have done 60 minute mashes at about 152 degrees. Originally I was having trouble hitting my OG, but I figured it out and pretty much nailed it on my third brew. But now after fermenting the third beer for 6 weeks, the FG has been stagnant for the latter 2 weeks at 1.027. I just bottled it and am certainly looking forward to trying it, but the FG was way off (13 points, where the first was 9 and the second was only 4). Every time, I aerated my wort and used a yeast starter. Thus I really doubt yeast health is an issue but of course I could be wrong. The Belgian IPA stopped at week 3 at about 1.030, so I added about 6 oz of corn sugar to try and get it going again. The yeast attacked it once I dropped it in, but the FG didn't come down much further. The temperature for each of these was around 65 degrees +- 3. I brought my Belgian IPA into a warmer room so it could stay at a steady 68 after the third week (also when I added more sugar) and it still didn't come down. I have been doing the mash in my 15 gallon brew kettle. I suspect my wort isn't as fermentable as maybe it should be. But I don't know what I'm doing wrong.
My question(s) is this: Before moving forward with another brew, are there any recommendations anybody has to ensure I can get closer to my FG? Would a high ph affect FG in this way? Should I be using a cooler for the mash instead of my stainless kettle? Should I increase the mash time? I have heard the that optimal ph for mash is 5.2 and that the mash process will reach this ph eventually. Should I start the 60 minutes AFTER I reach a ph of 5.2?
There was never a problem with attenuation or FG being off. If anything, my FG readings were below the target. I didn't realize there was a wort correction factor when using refractometers for FG readings.