« on: February 11, 2015, 10:32:31 AM »
If your sanitation is good, and you refresh it regularly, it will be good for quite a while. I do this regularly. I buy 50ml sterile centrifuge tubes, ebay or Cynmar, and whenever I make a starter, after decanting, fill a tube or two, mark it and put it back in the fridge. The tubes are graduated, so after they settle, you have a pretty good idea how much yeast you have harvested, then you can use a calculator and just step it up next time.
I usually dump it after about the 5th generation as I know home conditions are not that sanitary, but you can taste the wort you decant and get a pretty good idea if you should use it again or not. Does it taste like the original batch or does it have a hint of sour? I have about 6-8 strains banked for use this way.
When I'm doing an all grain batch, after I've sparged, the runnings usually still have a lot of sugar, so I add a couple more gallons to the mash and let it run off while I'm brewing. At the end of the day, I then take that run off and either boil it down or dilute it to my desired OG of around 1.030 and pressure can it. That way I've always got readily available wort to start my refrigerated bounty.