How much does fermenting temp really matter?

On saturday I brewed tranceamerica's Basic ME Pale Ale v.2. As I recently obtained a fridge I figured Id put it in there to help keep it cool during fermentation, what I have to ask is this-- How much does a fermentation temperature difference of 10 or 6 degrees make?

The recipe calls for 21 days at 70 and on average Ive had it at about 64*. Will this slow the fermentation making it need to ferment longer? or will it just come out a bit different? I can return it to the fan and towel method to keep it ~70* need be, but I probably wont have my keg build materials for about 3 weeks, so i could also let it ferment out in there.

Any input would be great.

thanks

Ferment a Whitbier at around 78, and another at 68...try them both and tell me if they are even recognisable as the same recipe!

a 10 degree difference is all the difference in the world to yeast.

Wow, ok... its obvious im still learning. Sooo, as its a basic ale (6.6 lbs light LME, and 2 oz of cascade hops) should I be fermenting this warmer? I doubt it would ruin the beer, but as I said, Im still learning. Any/all input is great!

I brewed a hefeweizen at 72-75* and got outrageous amounts of banana nose and flavor. Washed the yeast and did the exact same recipe but fermented between 60 and 62*. Fermentation is quite slower, after a week hydro is still at 1.024 where as at 75* it'd be in the keg conditioning right now. The nose and flavor of the hydro sample was also quite pineapple-y. I brought them temp back up to 70/72 range to finish out fermentation and maybe get some banana esters out of the yeast. My hefe is gonna taste like fruit punch by the end i think!

This is my first experiment with temperature variation, but I think for the ale you're brewing your temp is good right now. You don't want esters and @ 64 I think you'll get a nice clean ale. Will most likely take longer to finish though, what type of yeast are you using?

Temp makes a big difference. Speed of fermentation; colder is slower, warmer is faster. Taste; cold is drier, warmer is more fruity.

Check this website out. All of your answers are here.

How to Brew - By John Palmer - Yeast

An important point: most lagers and ales turn out better at lower temperatures, provided you stay in the yeast's range. Your Pale Ale falls into this group.

Some styles need to be brewed at the high end of the yeast's range, Belgians, hefes, etc., because the characteristic flavors of the style only develop at the higher temperatures.

JoMarky said:

Will most likely take longer to finish though, what type of yeast are you using?

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I figured it may take longer to ferment out... ok, thats fine, the fermentation has definatly slowed down since i cooled it down. Will varying fermentation temperatures hurt the beer? Im using safale us-04 instead of notthingham ale yeast as the recipe asks for, but Im pretty sure its a good sub.

I agree its a good sub, and its range is 59*-75* so you should be fine. I've read it can be a bit more ester-y than the Nottingham, but fermenting at 64* should help combat that. It's always best to keep fermentation temps as constant as possible (I know, i'm not following my own advice) but I think that advice is more focused on daily fluctuations rather than a single temperature adjustment.