Fermenting Temperature Variation - Stout Concerns

Process:

1. We made a partial-mash stout, learned that our hydrometer was busted, so couldn't get an OG reading. Recipe put it in the range of 1.090 to 1.105.
   
2. Aerated wort, pitched Wyeast Irish Ale Smack Pack yeast at about 72 degrees. (It had been properly SMACKED before we started the brew sesh).
   
3. Next morning I find out that my supposedly warm spot for fermenting has gone cold. Fermometer is reading 60 degrees. Move carboy directly on top of forced air heating vent and go to work.
   
4. Come home that evening and the beer is ALIVE! 1-2 bubbles per second in the airlock, 2-3 inches of foam/krausen. Temp is too high for fermometer to read, so I grab an insta-read thermometer and hold it to the glass - it reads 81-83 degrees, depending on where I hold it.
   
5. Move the carboy to directly next to the heating vent - within 24 hours the temp levels out at about 72 degrees (yeast packaging recommends 70-75 degrees). Bubbling slows, and at my 72-hour obversation point since pitching the yeast I find that the cake has dropped from the top of the carboy and settles at the bottom.
   
6. Today, at the 84 hour mark, there is a bubble every 20-30 seconds in the airlock.

This is our first time fermenting in glass instead of the plastic bucket, and the first time we've ever had the variation in temps I have described above, and our first stout, so I want to know:

• How will the temp variation affect the final beer? Will it affect the yeast's ability to do its full job - or just the time I need to let primary fermentation finish up?
  
• Did the yeast cake drop at the "normal" time?
  
• Should there still be more visible activity?
  
• Anything I can do now to improve the outcome?
  
• Any other constructive criticism?

Thanks everyone.

next time I would say let it warm back up a little slower than placing it directly on the vent. Second if it drops to a temperature that low, you'll most likely just have a slow start to your fermentation which is fine. You probably won't notice anymore fermentation other than changing hydrometer reading. Lastly just let it sit there for 2-3 weeks and let the yeast do their thing and clean up after themselves. From listening to these guys for awhile I can tell you that your beer will be great and to just trust the yeast and be patient.

Yeah, next time we'll do a few things differently. Would there have been a danger in the yeast sitting at too low of a temp for too long? That's why I put it right on top of the heating vent...

Next time you make a beer that big, be sure to make a starter in advance. In fact, it's always a good idea to make a starter when using liquid yeast, but with a big beer it's virtually mandatory.

Between underpitching and the wild temperature fluctuations, I'm betting your yeast were thoroughly stressed! I'm of the opinion that a low/high but stable temp is better than wide temperature swings. 60F is not all that low (I ferment most ales at 63F) and simply moving the carboy to a slightly warmer location would have been preferable. Unless you're making a Saison, temps in the 80s are off the chart!

All that being said, it sounds like your yeast are making the best of it and doing their job. Just stabilize the temperature as much as possible, and let it ride for a few weeks. I'm guessing your beer will have estery off flavors, but time will diminish that, and it will still be beer. Heck, maybe you've pioneered a new style...Imperial Saison Stout!

You really need to look into making starters, especially for a brew this big. You may get some off flavors from the high fermentation temp, but stouts can hide a lot, especially since this one will need some serious age on it anyway.

Thanks - we will look into starters for our next big beer, and be very patient with this one.