Poor Attenuation

Hi All
I have a continuing issue with poor attenuation in ales. As an example here is the porter I did 3 weeks ago.

5 gallon batch
9.00 lb Pale Malt (2 Row) UK (3.0 SRM) Grain 77.25 %
1.00 lb Mild Malt (4.0 SRM) Grain 8.58 %
1.00 lb Munich Malt (5.7 SRM) Grain 8.58 %
0.40 lb Chocolate Malt (450.0 SRM) Grain 3.43 %
0.25 lb Black Malt (Thomas Fawcett) (660.0SRM) Grain 2.15 %

Mashed at 153F. OG was 1.072
Aerated with an air pump. Pitched 2 sachets of S-04 at 65f

Fermented at 63 to 65F. About 6 hours to start. Good activity for about 40 hours. 2 weeks later I was at 1.020. It never moved any lower. According to Beersmith, that is 57% attenuation.
The beer is very good. A bit sweet and pretty rich.

I get this same level of attenuation in all my ales. Regardless of type. I do not have the same problem with my lagers.

I have been all grain brewing for about 3 years and this has been a problem for most of them. Therefore I am of the belief that there is something amiss in my process.

I welcome the input of the community.

grazie mille

Some thoughts:

• Have you checked if your mash thermometer is calibrated correctly?
• Have you tried using different yeast strains and making yeast starters with liquid yeast?
• What are you doing for fermentation temperature control?

The first thing I thought of was at 153, that beer should have gone to 1.012 or so. Can you double check the calibration of your mash thermometer?

The second thing I thought of, "Why do the lagers attenuate better? What are you doing differently?"

1) 11.65 lbs of grain = 1.072. That's over 85% mash efficiency - Real good.

2) 1.072 to 1.020 = 72% attenuation. Might be done.

Suggestions (for future batches):

1) Check your thermometer to ensure you are mashing at the correct temperature.

2) Mash at a lower temperature (149-150).

3) Replace a pound of grain with 2/3rds of table sugar.

My beers have been overattenuating beyond the predicted FG. I mash at 152, ferment for a week at 62 to 65 then bring the fermeter up to 72 to let the yeast finish. The early part of the ferment when there is lots of activity sets the flavor profile of your beer so that is when you want to keep it cool. As activity decreases the temperature inside the fermenter goes down and I think the yeast consider that a hint to go to sleep.