Like the question says, the pack arrived pre-smacked! I'm making a yeast starter before I brew so that'll tell me whether the yeast is ok, but what I need to know is whether to keep it in the fridge when it's in this state. (A great answer will give me insight into why I should or shouldn't.)

3 Answers 3


Yes, keep it in the fridge if you don't plan to use it in the next 24 hours. There are two reasons:

  1. The lower temperature will reduce yeast activity, reducing the buildup of more CO2.
  2. The lower temperature will reduce the pressure of the gas already in the pack.

As well as these reasons, Wyeast recommend you store the pack (swollen or not) in the fridge to maintain viability.

The only time I wouldn't put it in the fridge is if you plan to use it the same day or the day after. Then it's best to keep the yeast warm so they don't go dormant. This will reduce lag times.

That the pack has already swelled is not a problem, just possibly an indication that it has been above fridge temperatures. It's not actually "smacked" - the small sachet of media is most likely still intact, and if you can get to it and pop it the day before using the yeast, that will be good, but not essential as you're making a starter, so you could also just cut open the pack and pour the yeast into your starter, and forget about the packaged media.

  • Nice to hear I'm going for my first try and thought I had to wait another few days for a new package. Apr 28, 2014 at 16:06

On the Wyeast site they recommend that swollen packs can still safely be sold to customers. They make no mention that refrigeration is necessary.

What are the causes of swollen packages? Can you sell them?

Swollen packages are almost always the cause of a small amount of sugar or CO2 being left in solution at the time of packaging. Upon shipment, CO2 can be released from solution or the yeast can consume the sugar and create a small amount of CO2. Cell autolysis, or cell death can also be a cause of swelling packaged. However, this is only in rare cases where the yeast is exposed to high temperature for an extended amount of time. If a package is swollen and has not been mishandled, it can be sold with confidence.

  • 1
    Wyeast don't mention putting in the fridge specifically when swollen, because the general advice - keep in the fridge until the day before you need it - still stands. The assumption is that the pack is refrigerated until it's used. If you keep the pack at room temperature it will have a much reduced shelf life.
    – mdma
    Sep 9, 2012 at 13:43
  • Yeah good point - I should have been more explicit. Sep 12, 2012 at 4:41

Mine arrived swollen as well. I put it in the fridge for a day and the swelling went down considerably. I was then able to pop the nutrient pack without bursting the whole package open. Fermentation began within 5 hours of pitching.

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