WLP 080 Fruity, banana, estery off flavor

[wabn8c]

I brewed a batch of Cream Ale and used the WLP 080 Cream Ale yeast in mid September. This is the second time I've brewed this beer, and this was the 4th generation for this particular yeast strain. A buddy of mine and I keep and swap slurries which is why it's fourth generation.

This batch of cream ale has a slight banana, estery flavor about it when I've racked it to kegs and took a taste test that the previous batch didn't have. I maintained a consistent 67 degree fermentation temperature in my controlled fermentation chamber. I should have had way more than enough cells to start with, as I used well over 200 billion cells according to the calculator. I don't use a starter with the slurry because I pitched the yeast slurry 2 days after harvesting it from a previous batch.

Any ideas on what is causing my off flavor? Is it a result of mutating yeast strain after multiple generations of use? Will this off flavor fade or condition out during carbonation over the next 10-14 days?

 

[BobBailey]

This yeast is a blend of several strains. A blend may tend toward characteristics of one or more of the individual strains depending on several factors. Among these factors are fermentation conditions of previous generations and how and when in the process the yeast is harvested. A search here on HBT will yield hours of reading on the subject.

Rather than harvesting yeast from the fermenter, I make a starter large enough to yield about 100B cells extra and save that extra in a White Labs vial. I treat it just as I would a fresh vial. My understanding is that the aerobic metabolism that occurs in a well aerated starter does not affect yeasts in the same manner that fermentation does and therefore greatly reduces the changes in characteristics from generation to generation. I would assume that this holds true for blends as well, at least to some degree.

Personally, even using the process I described, I limit my use of individual strains to 5 generations and blends to 2. Why take a chance at ruining a batch over a couple of bucks?