Porter stuck fermentation, even with 2 packets yeast 1.026

Brewed a robust porter, all-grain, Had to add DME to bring the gravity up since my MLT is too small. Overshot the 1.069 recipe OG, got 1.073. After cooling gave it a decent shaking/aeration in the carboy (although I'm can't remember about how decent it was, since we had consumed many homebrews at this point). Added 2 packets of Safale S-04 at about 75 F.

Here's where I think we may have gone wrong. Over the next 8 hours overnight, the carboy sat in front of an open window (cold air)... Temp dropped to about 60 F, and fermentation had begun. Moved the carboy where the fermentation continued very vigorously at a steady 67-68 F for 3-4 days with lots of blowoff initially, then crawled along for a while.

It's now been 3 weeks in the primary. I've never had a stuck fermentation, so I started racking it to the secondary and measured the gravity during the transfer... 1.026. Ruh-roh. We finished racking it (took as much yeast with it as we could once we saw the gravity, and added another pack of S-04.)

Grain bill was:

6 lbs row
2.5 lbs Munich malt (10 °L)
1.25 lb Crystal 120L
9 oz Carapils
9 oz. Chocolate malt
7.0 oz. Black patent malt
+ ~2 lbs extra light DME

Mashed at about 155-156 for an hour. By the way it's the Avery New World Porter clone... lots of columbus and fuggles. It tastes great, but there is a barely detectable sweetness still there that leads me to think this isn't quite done.

I just couldn't believe with 2 packs of fresh S-04 this thing couldn't attenuate all the way. Any thoughts?

You used nearly 15% crystal malt, which will increase the FG significantly. You mashed pretty high, so conversion was probably not very complete. Also, S-04 is a high flocculating, medium attenuation yeast, so it will leave some residual sweetness.

All of those factors point to a high FG. There's not much you can do to fix it now. Adding amylase enzyme (i.e., Beano) will probably dry your beer out. With over 6% alcohol, it should be slightly sweet, but not too objectionable.

Yuri_Rage said:

You mashed pretty high, so conversion was probably not very complete.

Click to expand...

Would it be an incomplete conversion or a complete conversion with more longer-chain sugars that wouldn't be fully fermentable?

Trying to keep my head straight here, and I'm not sure I'm reading Yuri correctly.

you could warm up the temp a bit to 70 or 71 to see if that will help the yeast finish out. You've already gone through the most important part of fermentation so you won't get any off flavors from raising it just a tad.

Update: So the bulk of the fermentation was carried out at 67 in a temp-controlled fridge. Of the 3 weeks in the primary , 2 were in that fridge, and the final week I had it sitting out at room temp (fluctuating from 69-75) to make room for another carboy. So I had ruled out the idea of raising the temp to get it going again.

But 2 days after I racked to secondary and added that extra packet of yeast + dry hop, it has started up again. Slowly at first (one bubble/30 secs), faster now (15 secs).

Funny thing is, I had an IPA that followed a very similar series of events to this beer. The gravity finished around 1.017 after fermenting at 67 F, but after I racked and dry hopped it at room temp, it started up again and dropped to 1.012. That yeast was S-05.

I doubt the dry hopping does anything, but some people have reported that the racking procedure causes the beer to restart.