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I just brewed with what I now realise is a rather old Williams Brewing Kolsch kit. The yeast is Wyeast 2565 Kolsch and the packet has already expanded. I have no idea when it expanded, so I assume it must be months ago and that the yeast has already died/gone dormant. The manufacture date is 07 Jul 2014.

I have already ordered a replacement yeast packet which will hopefully arrive towards the beginning the week.

I have chilled my wort and it is now sitting in the fridge, where I can control its temperature. Right now I have it at normal refrigeration temperature (4°C). I will raise up the temperature suitable for fermentation before any pitching.

Should I:

  1. Pitch the expired yeast packet now and just let it be?

  2. Pitch the expired yeast packet now, then also pitch the new one when it arrives?

  3. Or throw away the old one and wait for the new one to arrive (and expand) then pitch that?

  4. Something else?

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I would just keep it refrigerated. If your new yeast are to arrive in two or three days, it'll be faster than testing old one. And assuming old one is dead, keeping wort at fermentation temperature is far worse than keeping it refrigerated. It's already chilled, keep it that way.

What I would try to do, and I hope you did if it was possible, would be to pour hot wort into container you are keeping it in, and close while hot. And maybe seal it the same way our grannies sealed pickle jars - by boiling whole container for a moment.

  • Already syphoned through a chiller into a carboy. The carboy is now sitting airtight in the fridge, where I'll leave it for now... – Digital Trauma May 15 '16 at 0:04
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    @DigitalTrauma If it was properly sterile, you are good. Now it's more important than with normal brew. Smell and taste before pitching and if you'll see any change, consider reboiling. But let's hope it'll not be the case. – Mołot May 15 '16 at 0:08
  • New yeast actually was delivered on Saturday afternoon - I didn't find it until Sunday morning - I smacked the pack which was already fully expanded by Sunday evening, so I was able to pitch then. Wort smelled and tasted normal then. Given this timing I'm glad I discarded the old expired yeast packet. – Digital Trauma May 16 '16 at 17:19
  • @DigitalTrauma glad to hear it turned all right. – Mołot May 16 '16 at 17:21
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I would take some of the wort and make a starter with the yeast. If the yeast is good it should start fermenting sometime in the first 24 hours. If it doesn't I would throw it in the drain and wait for the new yeast to arrive.

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    I don't really have equipment for making starters, and I think I'll heed @Molot's advice not to disturb the wort further for now. However, if I get time, perhaps I'll do a "science experiment" with my kids and pitch the old yeast into a sugar solution - can't do any harm - if its alive, then great; if not then I'm only out a bit of sugar. – Digital Trauma May 15 '16 at 0:06
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    Good advice - but only if you mean DME-based wort, not the one in fridge. Main wort should not be put at risk of contamination. Not now, when situation makes risk much bigger than usual. @DigitalTrauma All you need to make a starter is a big jar and patience. Everything else just make it easier, but nothing is critical. – Mołot May 15 '16 at 0:56
  • For the experiment you could put the yeast and sugar solution into a clear plastic bottle with a balloon on top. The CO2 will inflate the balloon. I would pour it out at the end of the day. – Chad Clark May 15 '16 at 5:42
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I wouldn't risk piching your expired yeast for a kolsch, this is a style that should have very low, subtle to no yeast esters. Your old yeast may be still have a partial viable cell count, but it would produce too many growth esters for the style.

If this was a style that has strong ester profile (belgian, wiezen etc). I would pitch the old yeast in hopes it makes some progress while fresh yeast arrives. Even if it was all dead, it would serve as nutrients for the fresh yeast.

In the future do a starter a couple days ahead of time, that way you can reschedule brewing if you can't grow enough yeast in time.

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