Problems since using a stir plate

[guypettigrew]

For the last couple of brews the harvested yeast has been started on a stir plate. Previously it's just been shaken whenever I've walked past it, but getting a bit more technology in seemed like a good idea.

The two yeasts were Whitelabs 001 and 007. Both had been used before, the 001 twice, the 007 three times.

The starter was 115g DME in a litre. Both yeasts created a krausen in the flask and there was far more yeast at the end of three days than had gone into the flask, about the same amount as when I was shaking and not stirring.

Within about 6-8 hours of pitching both yeasts showed bubbles through the blow off tube and had a really fast action for two or three days, then slowed right down. Today, 6 days after pitching a 1.059 beer with WLP001, it's only down to 1.030 and going really slowly. I would have expected it be much closer to 1.015 by now. The previous fermentation using WLP007 did the same.

Is there any reason to think changing to a stir plate could have caused this change in behaviour of the yeast? Or is it just an evil co-incidence?

Guy

[Troutman47]

I don’t think it’s to do with the stir plate, I’ve changed recently and still getting great results using 001, 005 and bringing on the yeast taken from bottles of Proper Job.

This sounds like a problem I had ages ago and I believe I found the answer in Chris Whites ‘Yeast’ book.

When do you take the yeast for reuse?

I was top cropping at 36hrs from the start of fermentation and it seems I was taking the lesser attenuating yeast.
Once I left it until 48hrs, which I read in the book, I’ve not had a problem with yeast fully attenuating.

Hope this helps and solves the problem?

BTW, I threw out the problem yeast and started again with fresh.

[guypettigrew]

Hi Troutman

Thanks, you've got me thinking. I changed two things when I collected the problematic 001 and 007 yeasts. The timing and the temperature.

Usually I wait until the beer is at about 1/4 gravity and bubbles are coming through the blow off tube very slowly. Then I drop the temperature to 10-12C, wait a couple of days and collect the yeast from the dump valve on my chronical. Then the beer's cooled to about 4C for another couple of days before kegging.

The last couple of times, for reasons which totally escape me now, the yeast was collected from the dump valve while the beer was still at fermentation temperature, about 19.5C. Lots of beer, not much yeast, but enough to make a starter.

It may be that doing it this way selected out less attenuating yeast. I know nothing about yeast, so this is only a guess. In the future I'll go back to my old ways.

A couple of new yeasts are on their way to me from The Malt Miller. I'll do starters with them and see how they go. That will sort out the query about using a stir plate.

I'll up the temperature a couple of degrees on the current sluggish fermentation to see if things can be hurried along. I need the fermenter again in a few days!

Guy

[MTW]

For me, the point of harvesting lots of yeast (as in a pitchable amount) is to avoid the need to make a starter for the following brew. You sound like your current brews are close enough together to avoid the need for a starter, by collecting enough yeast to repitch without it degrading too much in the fridge.

If you're planning to make starters, then I would just take a smaller amount of yeast, or even a PET bottle of yeast-heavy beer after 36hrs from near the top, allowed to ferment out [a method given by 'IPA' on here]. I've done the latter with 007 a few times now successfully, although the last starter lagged for nearly a day, with the bottle having been stored six weeks or so. You don't need much yeast for a 1L starter, but it does want to be healthy and not poorly selected, as you're aware.

Other thoughts are whether you harvested yeast from a particularly high OG beer, or whether there was a temperature shock anywhere. Stir plates can give off a lot of heat, giving the potential to shock it when it is pitched into a cooler batch. It wouldn't hurt to shake the stirred starter at the outset anyway. I've read views that stir plates are better at getting rid of CO2 than oxygenating. I haven't used mine for a couple of years.