What attenuation percentages have people actually seen with this yeast?
The back of the package specifies the attenuation as "HIGH", but my own experience suggest that it is medium or low.
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The attenuation rating for yeast is meant as a way of comparing one strain to another using a standard wort. It may not reflect the attenuation you can actually expect. The actual attenuation is much more dependent on wort composition than attenuation rating. Using the same yeast I can get anywhere from about 60-85% attenuation depending on the wort.
I made the following beer:
90% malted 2-row barley 10% flaked maize mashed between 66 and 69 degrees celcius 1.043 original gravity fermented with M79 1.011 final gravity
Had I fermented this with my usual Nottingham, I would have expected this to get down to around 1.007 FG. I fermented with M79, and it only got down to about 1.011 (about 70% attenuation).
(The beer has been in the bottle only for one week, but so far it's tasting very nice.)
Here is some support for my belief that Nottingham would have attenuated this quite a bit further. I brew with what I call a "parallel parti-gyle" system which allows me to make 2 beers (with potentially different gravities) from the same wort. The other beer I made with this wort yielded:
1.052 original gravity fermented with Nottingham 1.008 final gravity
It could be that your pack wasn't as healthy or fresh as what you are used to seeing with Nottingham packs. I saw several other posts online of poor fermentation characters from this same yeast.
So comparing the attenuation from one manufacturer to the next might be a little misleading. I'd had to see how low attenuating mangrove jack yeast strain would perform based on this data.
If you were doing true partigyle it is possible that the second runnings started to pull a little more non fermentables from the mash too. But your method of PG might be different from mine, so YMMV.