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About to brew for the first time. Making an IPA and bought Nottingham yeast which I just discovered says to keep at between 5-10℃ on the package.

It's unopened but been at between 20-32℃ (those are the outside temps in my city) for about 3 weeks now. I just put it in the freezer (0℃) for 6 hours and then just the fridge (5℃) when I discovered the temperature advisory on the packaging today.

Has it gone bad and do I need to repurchase it? Asking since it's a bit of a pain to source it again in my part of the world, I had bought it from the US

5

This depends entirely on if it was liquid or dry yeast.

Active dry yeast is very hardy. Most dry yeast strains can be kept at room temperature for 3+ months with negligable impact on the final product. Anecdotally I've gone even longer and still had a strong fermentation.

https://fermentis.com/wp-content/uploads/2017/10/SafAle-BE-256.pdf

STORAGE During transport : The product can be transported and stored at room temperature for periods of time not exceeding 3 months without affecting its performance.

To answer the original question for others who may find this link:

Yeast stored at 30℃ for 3 weeks would be perfect still.

~~

Though you said you put it into the freezer, this is where you might have done some real damage. As Evil Zymurgist said, if it's dry yeast you might be okay, just make a starter, and if they are still viable just let the yeast recover it's strength before you use it.

If it was a liquid yeast, and it froze solid, they are all probably dead.

If the liquid yeast was still 100% a liquid when pulled it out of the freezer, then just make a starter; They are probably fine.

4

If yeast freezes conventionally (not cryo) it's dead. Ice crystals form within the cell and rupture cell walls.

Edit: If it's dry yeast. There's a good chance it's not beyond hope. Use it to make a starter to proof it and hopefully grow more healthy yeast.

  • Even if for just 6 hrs? – flak37 Mar 17 '18 at 22:51
  • Also would it have been usable if nor frozen? How would the high temps affected it?? – flak37 Mar 17 '18 at 22:52
  • @flak37 yes at 0°c or 32°f for 6 hours would at least severely damage most cells. Had it only gotten to 32°c / 89°f it would have been fine. – Evil Zymurgist Mar 17 '18 at 23:02
  • 1
    if it was liquid yeast, yes. Not for dry, though – Denny Conn Mar 18 '18 at 16:10
  • @DennyConn true, it's not as bad. But dried yeast still has about 20% of it's moisture. Some brewing yeast dehdrate down to as low as 2%. Most yeast makers agree freezing dry yeast doesn't kill all of it but does "damage" it as a whole resulting in significantly lower viable cell count. – Evil Zymurgist Mar 18 '18 at 17:40
2

Shouldn't be a problem at that temp for that short time

2

Lalvin used to have a bunch of useful articles at http://www.lalvinyeast.com/articles but luckily there's the web archive. Here's a summary of two on the topic of yeast viability and storage.[2] [3]

Freeze-dried yeast survives best frozen, but the biggest factor regardless of temperature is oxygen damage, thus want to store it vacuum packed. In original oxygen free vacuum packing at < 5% moisture, they will lose 20% activity per year at 20°C (68°F), 5% at 4°C (40°F). Additional moisture and oxygen will increase rate of deterioration. Therefore the viability will decrease much more rapidly once opened and so have to compensate by inoculating with more yeast.

Another very important factor is proper re-hydration.[4] Rehydration in distilled or deionized water is lethal to the yeast (due to cytolysis) . Rehydrating in 15°C (60°F) water can kill 60% of the yeast. Tap water at 250ppm hardness is optimal. I've also heard to not pitch yeast with > 10°C temperature differences since it shocks the yeast resulting in further loss in viability.

I once found a package of EC-1118 in the freezer with expiry of 2005-04 (so packaged in 2003) and rehydrated & pitched it 13 years later and surprisingly it worked just fine.

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