There is an off-flavor in this batch that cannot be attributed to anything other than the culture. Granted, the beer is a very naked example, but a quality culture handled correctly would not have this off-flavor. Additionally, the culture has a significant percentage of non-flocculent cells (i.e., it is powdery). There is little doubt in my mind that W-34/70 is undergoing mutations during aerobic propagation. I will not use it again.
Yikes, this is information that I have not heard before. Thanks for sharing. However, my taste threshold isn't nearly as sensitive.
I recently purchased two sachets of 34/70 and two of Diamond to try them out and compare them for myself. Now I'm thinking I should try a third batch with liquid yeast to compare as well. Surely other homebrewers have performed this hundreds of time, but I learn more from my own experiences.
My followup question is, does the drying process somehow result in these mutations you detect, or is this lab or even batch specific? Or is this yeast just different from the specific CL-660 culture you remember?