So I’ve been rinsing and saving yeast for a little while now. I know a rule of thumb is that if it’s been less than about a month it’s ok to just pitch and if it’s over a month or so you should make a starter. But what date are you using to figure out that timeline? Is it the date you first pitched the yeast in the last beer? Or the date you collected and rinsed it? I assume the original pitch date since that’s when the yeast multiplies so to me that would be considered the ‘born-on-date’ if you will.
I have some Wyeast 1728 Scottish Ale that I originally pitched on Oct 14th and rinsed and collected on Nov 6th. I’d am going to use the 2nd gen this weekend and am not sure if I should make a starter (I feel I should) or just pitch what I have. The beer I’m going to be brewing should have an OG of 1.065.
Good question and I have wondered this for a while. BUT, this last weekend I brewed two batches. One I pitched using 2/3 of a yeast cake from a Rye IPA that was about a 3 weeks from brew date. The other was using harvested yeast that was about a month old, from the harvest date. The first was fermenting 12 hours later. The second was going well 24 hours from the time I pitched. Both are still cranking away.
I’d assume a 50%/month viability loss while the yeast is at room temperature, starting near the end of active fermentation, then 25%/month while it’s stored under beer in the fridge. Based on some cell counts I’ve done that’s actually a little conservative, but I’d rather go that way than assume there’s more yeast than there actually is.
That would put your viability around 60%, which is low enough that I’d make a starter. As a general rule, I don’t re-pitch below about 80%.
I would consider the date that active fermentation stopped and how it was stored since then. If you harvest within a few days after fermentation and stored under beer in the fridge it will still be in good condition and ready to go after a month. If you left in in primary at room temp for a few weeks before you put it in the fridge then I would feed it if you use it after 3 or 4 weeks. After a few months feed your yeast.
Assuming that most ales complete their most active fermentations within the first week, when you harvest and label yeast, you would put that date? And create a starter if you were, say, 6 weeks away from your initial brew day?
Yes on both. I would put the harvest date on the jar and I would take it out and feed a day or two before you brew if you have stored it more than 2 months.
I label the jars with the name, harvested date, generation and OG of the beer. I assume the brew date was 2-3 weeks earlier, so the yeast is that much older. But I’m starting to think that a starter needs to be made most of the time. So why not be sure and just make one. Because the yeast is a minimum of 3-4 weeks old anyway… and usually older.
