Unexpected final gravity...

Since my return to brewing, I'm a dozen batches in and starting to dial in my process and feeling confident about things...

Today I got a FG of 1.020 on a batch that I expected to get down to 1.010.

It's a pale ale that I've made before, except that I upped the grain bill a little bit (SG 1.064). I used slurry from a previous batch with a similar recipe (S-05). This is the fourth pint jar that I have pitched from the harvested yeast. The other three pint jars worked perfectly on very similar recipes... Nothing looked off when I pitched it. I had activity less than 6 hours after pitching so I thought all was well.

Do you think this is because it was the last jar of the bunch and sat in the fridge three weeks? Another possibility is that the ferment temps may have been lower than the first batch (lower 60s F instead of mid to upper 60s). It fermented for 4 weeks, which has been more than enough time previously.

It's too late to do anything about it this time because I've already kegged it and washed the bucket out, but I'm just looking for some ideas on what might have happened.

 

Did you hit your mash temps? How much specialty grains were in your recipe? I highly doubt it was your yeast.

 

Since your fermentation took off quickly I wouldn't suspect that the yeast was too old. Lower 60s is fine for US-05.

When you upped the grain bill did you just increase the base malt, specialty malts (crystal, etc) or both?

If you increased everything proportionally then you should get a slightly higher FG than the previous brews but it shouldn't be 10 points higher.

Check your thermometer in boiling water. If it reads low then you're probably mashing higher than you think.

 

I'll have to look at my notes when I get home, but I didn't think the mash temp was off. I suppose the thermometer could be inaccurate, I'll have to look into it.

The grain bill was increased proportionally.