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Jan 29, 2013
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JUst read very good article in recent BREWSMITH newsletter on yeasts

Ale yeasts ferment in the range 10-25C and produce beers high in esters and often lower in attenuation, both distinctive characteristic of ales. Ale yeast strains are often mixed together to aid in attenuation and flocculation. Lagers ferment in the range from 7-15C and produce a cleaner beer with lower esters.

What exactly is the role of esters in brewing? I know its out there, but I am getting lazy in my old age (besides, Larry, Nosy, Mad Ferm, et al will give a concise definitive answer)
Esters are chemicals that produce fruity flavors in beers. For example, the banana flavor in a Hefeweizen is due to an ester. Esters are present in every beer in varying amounts. You don't want a lot of them in, say, a Pilsner but in a Saison they're indispensable. They only become a problem when there are too many of them and the fruity flavor interferes with what you want to taste or throws your beer out of balance.

Does that help?
That quoted paragraph is too general to be useful in my opinion. I would say most English and Belgian strains are on the estery side, but a strain like US-05 is very neutral. Fermentation temperature impacts ester production - higher temps = more esters = more flavor impact, and not necessarily a good thing.
I'm far from an expert but I will say that I've been having a good time experimenting with different yeast strains to determine what produces the best results for me. I have used the same ingredients for each of my last two 5-gallons batches; on the first, I used just one kind of yeast. On the 2nd, however, I split it into two 2.5 gallon amounts and pitched different yeasts in each. So now I can basically do my own homemade flight of beers with the only appreciable difference being the yeast. From the aroma alone, I could tell the difference; the first was a dry wheat yeast (Safale WB-06) and I felt like it was too estery, though that could have been due to higher-than-optimal temps. The split batch, however, was much more in line with what I was looking for; I used Nottingham dry in one and Wyeast American Ale in the other, and the gravity samples show subtle differences. All bottled, just need some time to condition now.