Dried yeast - can it be bad?

[rickthebrew]

I bought a 500g block of us-o5 a while ago ( a few months) it was all sealed in a proper foil vac pac bag and was intact. I opened it and froze it down in a tub in the freezer. I did a couple brews with it in the mid summer and both brews took on a sort of chemical smell almost like acetate - quite strong and you could also taste it in the brew - i thought maybe i`d pitched the yeast at too high a temp or the air temp was too high? I deep cleaned all my kit and bought a new FV and the next brew with the same dried yeast had the same problem -not quite as prominent but definetly there, after bottling the taste and smell was still there and over time it did fade but the hop flavour and aroma was not what you would expect. I`ve done a few brews with nottingham and s-o4 since with the same cleaning and pitching regieme and these have been fine - so is it possible for dried yeast to be off or infected ? I made a starter with the us-o5 last night to see if the smell is there again - and was extra careful with temps and cleanliness.

Any ideas - i really don`t want to loose another brew or have a bad tasting one

 

[Aleman]

Simply put Yes,

The instructions on the packet clearly state use within one month after opening.

I take great pains to exclude air / moisture from the large packets I buy and they do last a long time . . . but the minute you get moisture in there lifespan is limited I'm afraid.

 

[rickthebrew]

The smell from the starter is the same is as before so it`s the bin for the yeast, will go back to using small packets and using yeast slurry - my SNPA clone will have to be pitched with nottingham or k-97 :wha:

 

[rickthebrew]

Used the k-97 in the end and chucked 30quids worth of yeast in the bin - lesson learned the hard way :P