WLP051 and Ambient Temps

I have 5 gallons of a Cascadian Dark Ale fermenting with this strain of yeast. I decided to ferment at 68 degrees but my mine concern is should the ambient air temperature be at 68 degrees or should the fermenting beer be at 68 degrees? I understand that while fermentation is happening, the temp inside the carboy could be about 10 degrees above ambient air temp. Could someone clarify what a good ambient air temperature is? Much appreciated.

The fermenting beer should be at 68F. Typically the beer is about 10F warmer than the ambient air. So you want the ambient air to be about 58F.

I have a question about this that i hope will benefit the OP as myself.

I have noticed when I set the ambient air temp to 58 it is fine until the initial fermentation is done (after about a week). Then the temperature of the beer will go to 58. What happens to the yeast at this temperature? There is still a lot of vital activity that is being performed by the yeast at this stage no? Yet at that temperature (i.e.58 degrees) the ale yeast will no longer be working and cleaning up diacetyl and other natural by products will it?

I made a cream ale recently that did not come out as good as one that I fermented at around 64 (ambient air temp). Could this be the cause? Everything else was done exactly the same, but this one had a slight diacetyl taste, nothing major but noticeable.

I have also noticed some lower gravity beer will only go up by maybe 4 to 6 degrees instead of ten. I ask this because my fermentation chamber can hold 6 carboys, with 6 different beers all in different stages of fermentation, and I am sometimes lost as to what to put the temp at. If I run the temp down to 58 degrees because I just got done brewing an imperial stout, then what does that do the beer that I brewed the week before and the one a month ago? They obviously are not actively fermenting and will go down 58 degree temp correct? What do you guys do?

I have noticed when I set the ambient air temp to 58 it is fine until the initial fermentation is done (after about a week). Then the temperature of the beer will go to 58. What happens to the yeast at this temperature? There is still a lot of vital activity that is being performed by the yeast at this stage no? Yet at that temperature (i.e.58 degrees) the ale yeast will no longer be working and cleaning up diacetyl and other natural by products will it?

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I'm not an expert but what I typically do is ramp up the temperature from the mid-low 60s to 68-70F once primary fermentation is coming to an end. This is typically about 2-3 days but it varies. I then let the beer sit at 68-70F for a couple days to allow the yeast to finish cleaning up. If your beer is dropped down to 58F right after fermentation I'm not sure the yeast will be doing much cleaning. This could be the cause of the diacetyl in your cream ale if you dropped the beer down right after fermentation.

I ask this because my fermentation chamber can hold 6 carboys, with 6 different beers all in different stages of fermentation, and I am sometimes lost as to what to put the temp at. If I run the temp down to 58 degrees because I just got done brewing an imperial stout, then what does that do the beer that I brewed the week before and the one a month ago?

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Ideally you'd want a separate temp control for each carboy but who has that. The beer in the chamber that has been done fermenting for a couple weeks should not be affected much. But if you have a beer nearing the end of fermentation while you drop the temp down for another beer you may stop the yeast from finishing their job.

Like I said, I'm far from a pro, but I've had good results with what I've been doing.