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high or low yeast fermenting temperatures?

Russell

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I normally just ferment at 67 to 68 F for most of my ales. The yeast has a low and a high temperature that is on the packet for best temperatures to ferment at.
Is there a difference in the beer if you ferment at a the low temperature compared to the high temperature? Which of these do you use the low or high or between?
 
Most often, yes.  It really depends upon the yeast you are using. 

In my experience, a yeast such as WY1272 (American Ale II) produces a very clean, balanced profile when used at 62F to 66F and produces some fruity esters when started at 68F and going higher.  The higher the fermentation temperature, the more fruit esters that particular yeast produces.

Other yeasts give off a different profile depending upon the fermentation temperature as well, giving off or emphasizing various esters or phenols with increased temperature.
 
With some exceptions, for example making a wheat beer using a hefeweizen yeast, I prefer a clean tasting beer with as little ester flavor as possible.  That's just my personal taste.  So as a general rule I use Fermentis Safale US-05 and Saflager S-23, and ferment at the low end of the recommended temperature range. I don't see any advantage to spending extra money on liquid yeast unless it is to impart a particular flavor to the beer, but it makes a huge difference if that's what you're after. In that case you want to choose a temperature suited to the specific yeast to produce the targeted flavor.

One of my first forays into brewing was during a hot summer, and I couldn't keep the temperature under 75.  Beer tasted like liquid bananas. It was pretty awful but I drank it anyway.  ;)
 
Also something to keep in mind is that the temperature in the car boy will likely be warmer due to the active yeast.  As such I usually try to keep my fermenter in the 63-65 degree range - or what would be the lower to mid range of the yeast target range.  Chances are if your fermenter is at 68'your beer is at a warmer temp.
 
I've been getting in to the habit of starting fermentation at the low end, then watching it as the days go by.  When things look like they're slowing down a bit, I'll bump up a few degrees at a time until I finally reach the higher end.  This higher end is essentially my diacetyl rest.  I hold there for a few days or more.  I take a gravity reading (or not if I'm lazy) then drop down a couple/few times to eventually hit -1 degree C.  This is my lager/cold crash. 
 
jtoots said:
I've been getting in to the habit of starting fermentation at the low end, then watching it as the days go by.  When things look like they're slowing down a bit, I'll bump up a few degrees at a time until I finally reach the higher end.  This higher end is essentially my diacetyl rest.  I hold there for a few days or more.  I take a gravity reading (or not if I'm lazy) then drop down a couple/few times to eventually hit -1 degree C.  This is my lager/cold crash.
[/quote

In my experience, this is a good way to manage your fermentation.  I start low also and allow the temperature to climb slowly over the first four days to a target high for the bulk of the primary.  It also gives me a feel for how fast the fermentation is progressing.  Usually at day 4, I am at my peak fermentation temp and can watch for when the fermentation chamber switches from trying to keep the carboy cool to when it is supplying heat to maintain temperature.
 
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