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I have an older packet of yeast that has been stored in the refridgerator past the best by date on the package. Is it still okay to use the yeast? Is there a way to test to make sure it's alive still?

  • It has been stored in the refrigerator for how long? I have successfully used packets of yeast that had been stored in the refrigator for a year. If not opened, or hermetically closed, that should still be OK. – chthon Jan 28 '18 at 10:00
  • I've only had it about two months and it's been refridgerator the whole time. But it's already past the manufacturing date. – jrquick Jan 28 '18 at 13:51
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Do a starter or simply "proof" the yeast as you would for bread before using.

You should run the yeast through a viability calculator to see how much you need to grow in a starter considering the age. Since proofing the yeast will only let you know some of the yeast is alive.

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With liquid yeast, you loose around 20% of viability each month after the manufacturing date indicated on the package.

If your yeast in 2 month old, it should still be 60% viable, thus you should be able to make a starter with it, in order to know how, check this link : https://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/.

It will allow you to calculate your pitch rate taking into account the viability of your yeast.

Another method can be to take a sample, dilute it, die it with methylen blue and count the alive/dead cells ratio under microscope to compute viability. (https://www.whitelabs.com/beer/cell-counting-viability-testing)

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