Lower than expected attenuation

[brewbama]

I recently brewed an ESB with 8 lb Golden Promise (89%) and 1 lb Double Roasted Crystal (11%) mashed at 153*F. Though I've read crystal malts can be used up to 20%, I rarely use more than 10%. I used 1% over my 'personal crystal limit' but I didn't think much about it.

I used S-33 yeast with this beer in an effort to brew an authentic English Ale. I pitched at 62*F and had a strong activity within a few hrs. As ferm activity began to slow after a cpl days I began ramping up the temp to 70*F to coax it to finish. Per the yeast spec sheet optimum temp is between 59-68*F.

My OG was 1.054 which was spot on my prediction and I expected a 1.016 FG (70%) but even after increasing temp the best I could get is 1.020 (63%). It's only 4 points and 4.5 vs 5% ABV so I threw in the towel accepting my 7% less attenuation and kegged it today. This is my Daytona party beer and I still have to cold crash, clear, and carb it this week.

I checked the thermometer I used against another and found them to be within 2*F so I feel OK there.

What do you think caused my 7% loss in attenuation?

 

[whovous]

How long did you ferment before throwing in the towel?

 

[brewbama]

How long did you ferment before throwing in the towel?

2 weeks. It finished after 4 days per my hydrometer.

 

[porterpounder]

I think average attenuation for that strain is 70%, so it did come in low, but who knows what happens with some of those crystal malts? If it tastes fine then go with it, if it's all sweet and cloying then maybe pitch a finishing strain and see if you can get it down a bit more. Maybe S-04.

 

[brewbama]

I am chalking this up to a natural product doing what nature pleases despite what I expected. The hydro sample doesn't taste too sweet. I expect the carbonation to give it even more 'bite'.

If the results are otherwise good, I may brew this again using 3% less crystal, lower mash temp to 150*, and when/if it stalls I think I'll gently stir the yeast back into suspension along with raising the temp to see it I can get that last 7%.