I normally try to re-pitch my harvested yeast the day I harvest or the day after. I harvest into cornies and am looking at having the yeast in the cooler for three days before being able to brew. I have pitched 3 day old yeast once before with good results but I thought I'd see what everyone's "rule of thumb" is regarding storage time of yeast before re-pitching.
It's all about the strain and the harvesting technique. If you're scooping it off the bottom of a ferm by hand and dumping it into a corny, you may have some issues with O2 pickup (I believe that it signals the yeast to use up their glycogen reserves), and you're yeast will be spent before they hit the ferm. If you can keep your slurry under N2 or CO2, cold, and pressure-free, I don't see why you can't keep it around for a few days.
Disclaimer: There are a few strains that I've worked with that don't do bottom-cropping and storage well, mainly Weiss and some weirder Belgians. I have seen the Chico strain go for well past a week in a holding vessel and come out all right, however, so there you go.
Normally 3-6 days is a good range, 2 weeks max if you must, especially for strains that aren't your house yeast. I feel that harvesting yeast at the optimum harvest point makes a huge difference as well. Getting to that sweet center of healthy mid-floccers (respectively) is key. It only takes one less than preferred crop of early droppers or too much dusty yeast to start putting selective pressure on a culture. I don't know if you do counts/vitality, but I always try to verify before pitching, as William said keep it vented and weiss strains don't do well with storage.
As South County said, cropping is vital. Go for the yeast in the middle of the cone. Also, if you are going to be keeping it for a few days up to a week or so, add some sterile water. If you boil the water most of the O2 will be driven off (just make sure you cool it down to cropping temp!). The addition of water helps reduce the stress that is brought on by the alcohol. Just remember, the cone can be a very hostile environment for yeast, so get them out ASAP.
This backed up what I thought. I am harvesting today and brewing Tuesday with wyeast 1272 and I can keep the O2 out so I think I'll be good.
Thanks again guys.
Hmmm. I have kept my Irish Ale and No Am Lager for well over a week without any problem. While cropping is a huge part of viability, general health in the previous fermentation is as well. Deduct for high alcohol-stressed yeast, yeast fermented out of their comfort temp range, high adjunct beers, incorrect zinc feeding...and the cropping/pitching of the previous fermentation.
BSI & yeast care
Check out the Brewing-Science Institutes web site's section on yeast care http://www.brewingscience.com/
Dave and Bryan at BSI are great people to talk to about yeast care and are very practical in the advice they dispense. Check out their site and you should get some good ideas on yeast handling & storage or have your good habits re-enforced by the information found there. The yeast they sell is great too btw.