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Harvested Scottish Ale yeast

I harvested some Scottish Ale yeast and used it in a new batch yesterday. It had sat in my fridge for 4 weeks and because of poor planning, I didn’t have time for a starter. I just let the yeast come to room temp and pitched. This had always worked before. But after 24 hrs, still no activity in the air lock. The only other variable which was different this time is that it was so hot and my tapwater not very cold so it took a lot longer to cool my wort and I pitched a little warm. I used a swamp cooler to get the temp down to high 60s where it is holding now.

My questions:

  1. How much longer should I wait before getting more yeast and pitching again?
  2. How long can I keep harvested yeast in the fridge and pitch?

If your sanitation is up to snuff, the batch will probably be fine…it’ll just take a bit longer for those middle aged yeasties to wake up.
I keep my yeast cakes in a flask or jar in a 33°F fridge and typically re-pitch without a starter within 2-3 weeks. Sometimes though if I’m on the road with a show, 4-6 weeks may go by until I can brew again. Sometimes I’ve fed the yeast up a day or two before brewing, but most times, I just run with what I have, dumping in a bit more than the usual 1/3 of the cake. It may take longer to restart, but for what its’s worth, in 25 years I’ve never had a batch fail because the yeasty cake was more than 4 weeks old. And even more significantly, the slow start never affected the quality of the brew in the end.
Try not to sweat it. If you don’t see activity beginning in another day or so, you can always add some dry yeast. But it likely won’t be necessary.

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