Unexpectedly low final gravity

[Queequeg]

Took two final gravity readings of my current brew, four days apart. 1st was 1.017 2nd 1.013.

Beersmith and the recipe estimate a FG of 1.018, so I am suprised at the low gravity.

On the first sampling the beer was still full of suspended yeast flocs that had yet to sediment. The beer tasted exactly as I suspect. No biofilm or signs of infection just yeast rafts floating about.

On the second sampling the beer was much clear and tasted again as I suspected.

The first reading was taken and day 10 and the 2nd day 14. Airlock activity is still on going if infrequent.

The mash temp was held at between 67C-69C the target was 69C. I mashed for the standard hour.

The yeast is wyeast ESB 1968, the grain bill is UK lager as a base malt with Crystal 10 and 60 and wheat and Munich malt.

The ferm temps started at 19.5 and have been ramping to 21.5 from day 3 to 6 where they currently remain.

The airlock is still active, I will retake the gravity again after Christmas but I am hoping it won't be any lower. I'm hoping its not any infection, it doesn't smell, look or taste infected.

Any ideas whats caused this?

 

[FensterBos]

Well, a 69C (152F) mash temp is going to give you a higher-fermentable beer so you would be creating more fermentable sugars, which would result in a lower FG, lighter body, and higher ABV%.

What was your original gravity? Using the ESB 1968 you should expect 65% to 71% attenuation - so if you started off with a SG of around 1.050 you would be in the right range.

 

[Queequeg]

My OG was 1.058, the Hydrometer is calibrated for 20C and all the readings have been taken within 1 degree C. The hydrometer reads 1 in water at 20C. So I am getting 77% AA.

 

[RM-MN]

I have an idea of what happened. You made your yeast happy. It happens quite often to me. You and I both start the ferment at the low end of the yeast's preferred range and let it warm when the ferment slows down. No worries.

 

[flars]

Wait a week after you see no airlock activity before you take a new SG reading looking for FG. The yeast will still be working after airlock activity has basically stopped. The yeast will then need a few days to clean up their work. Patience is golden.

 

[fishersfirst]

Well, a 69C (152F) mash temp is going to give you a higher-fermentable beer so you would be creating more fermentable sugars, which would result in a lower FG, lighter body, and higher ABV%.

What was your original gravity? Using the ESB 1968 you should expect 65% to 71% attenuation - so if you started off with a SG of around 1.050 you would be in the right range.

I think you've got your conversions wrong. 69C is 157F. The expected FG should be higher as the mash temp is on the high side.
Having said this, I often find that Beersmith underestimates the level of attenuation.
British yeasts often land up slowly chugging away for a while, to the point where I have a brewing mate who often does not use priming sugars when bottling his english ales as they continue to attenuate in the bottle.

The FG you have at the moment is not surprising.

 

[Queequeg]

Thanks for the input everyone. I'll keep you informed as to the result of my 3rd reading.

 

[FensterBos]

I think you've got your conversions wrong. 69C is 157F. The expected FG should be higher as the mash temp is on the high side.
Having said this, I often find that Beersmith underestimates the level of attenuation.
British yeasts often land up slowly chugging away for a while, to the point where I have a brewing mate who often does not use priming sugars when bottling his english ales as they continue to attenuate in the bottle.

The FG you have at the moment is not surprising.

Stupid Google.

...and stupid me for using it.

 

[Queequeg]

update;

I took the third FG reading today. It came out as 1.012, so think it pretty much done. The A/L activity has stopped so I went a head and dry hopped.

21 days fermentation, that was a long one.