MyQul
Chairman of the Bored
Not wanting to hi jack the thread but, as you appear to have a penchant for old yeast... the first brewing book I read was Greg Hughes and I seem to remember that he said that yeast can only be reused a few times (I can’t double check as a mate has ‘borrowed’ it). I have reused yeast many times and it has fermented vigorously and taste doesn’t seem impaired. I’m currently conditioning a Hefeweizen that was brewed with yeast which will have been in around 8 to 10 previous brews. What’s your view on how often it can be reused? À propos of nothing, I’ve also made some great bread with it.
I agree yeast can be used many times but eventually you do get some 'drift'. If say, you repeatedly harvest from the bottom of the fermenter eventually the yeast becomes very flocculant and as a result this lowers the attenuation. I remember a previous forumite seeing how many times he could reuse yeast and iirc it was about 11 times before the above happened.
My favourite technique is to harvest as much of the yeast cake into a jar and keep it in the fridge. Then just take a spoonful or two of this and put it in a starter whenever you want to brew. The jar of yeasts lasts many months, doing this