Originally Posted by firenemus
...well, my brewing space at least.
I brewed a RIS for the first time this weekend, and I tried to follow Jamil’s tricentennial recipe (from his “Brewing Classic Styles” book) as close as possible. The SG was around 1.098 when I pitched (plenty) of Irish ale yeast (wlp004). I vigorously shook the carboy for around 3 minutes after pitching and then injected O2 with a diffusion stone for about another 2 and half minutes. The house and wort were around 68*-70*F at the first sign of fermentation, which only took about 1/2 hour. Jamil wrote that this beer would benefit from a little diacetyl so he recommended keeping the fermentation temp at 70*F. The next morning I was happy to see that the thermometer strip on the carboy was reading right around 70*F and the air-lock was bubbling away. When I got home from work that same day the temperature had gone up to about 74-75*F and I noticed that the krausen (which was never very big to begin with) had died down flat. I placed the carboy in my brew fridge which was set for another beer at around 65*F. Within a couple of hours the temperature of the carboy had dropped to around 66-68*F.
So...here are my questions/concerns:
1. Fusel Alcohol
I really can’t find any information (that’s clear to me at least) regarding the temperature at which fusel alcohol is produced. It appears that it is produced at any given temperature, but becomes excessive at warmer temperatures. I also understand that higher gravity worts can also contribute to its formation.
Do any of you know what that temperature threshold would be? Do you think allowing the beer to reach 75*F will have caused any adverse affects?
A lot will depend on the yeast that you use for it. Generally, the higher the temperature within the temperature tolerance range for your yeast, the more stressed they will be. A RIS is a big stout with a lot of fermentable sugars, ideally, should have a long slow fermentation on the cool side of the tolerance range.
2. Head Retention
I have some experience with wlp004, and typically the krausen will last at least a couple of days (not like wlp001 which seems to last forever). This time it lasted less than 24 hours. Looking at the beer, it appears to be fizzing as the bubbles pop once they reach the surface. I’ve read that fusel alcohol (among other things) can contribute to poor head retention. I felt my mash went well, although I ended up mashing at around 152*F for 90 minutes instead of 149*F as was mentioned in the book.
So is this just characteristic of this particular yeast strain? Was my mash too warm to hold for 90 minutes? Am I too concerned about fusel alcohol?
Yes, you're probably too concerned about it. I think what you're experiencing is totally normal. There are a lot more factors than yeast that can affect head retention. Additions of some cara-pils (cara-foam) or even just a little crystal 10 can significantly boost your head. Every fermentation is different, even with the same yeast strain. You can occasionally get a feel for a strain and it will consistently perform the same way for years, and then suddenly throw you a curve ball when you use it on a different wort or for not apparent reason.
3. Temperature Fluctuation
Typically I do a better job keeping the fermentation temperature of my beers a little more stable. But this time my thermowell was being used by another beer so I just tired to guess what ambient temperature would be appropriate.
Did I create more problems for myself by cooling down the carboy almost 10*F?
It depends on the yeast. A consistent temperature within the range of the yeast is what the yeast themselves prefer. Probably the most important step in the fermenting process is keeping the temperature stable and in the desirable range of the yeast. With fluxuating temperatures, you're sure to get stressed yeast. As to how bad the problem is, it's going to depend on the yeast's vigor.
4. Aeration (last question - promise)
As I mentioned previously, I aerated by shaking and using O2 and a stone. So I feel it was adequate. However, this is a big beer and I understand that a little aeration during fermentation may help it finish and not get stuck.
Would any of you recommend aerating at this point (pitched on Monday – haven’t read current SG)? If so, should I just shake it up or pump in some more O2?
I'd leave it alone. This is a high gravity beer and it will have a high gravity finish. In fact, if it finishes too low, it'll have that "hot alcohol" burn on your tongue, which is something you don't want. I'd rather see a RIS finish on the malty sweet side than on the dry hot side.
I’d like to thank those of you who’ve managed to read this entire post without clicking away out of boredom. And I’d like to thank any and all of you for your suggestions and/or constructive criticism.
May your carboys and kegs be eternally full!