As evidenced in a search of this and other forums, the topic of dry yeast storage longevity and expiration dates comes up semi-frequently. The consensus seems to be that it is just fine to use expired yeast (within reason), especially if it has been refrigerated. I also see a general consensus that yeast aging rates in pitch rate calculators, even as a first order approximation, are not terribly reliable. I’ve generally not worried too much because I keep my dry yeast fridged and don’t let them sit around for too many years. But, I’m still curious as to how far I can push the envelope.
So…are there any actual data on this topic? I’m specifically thinking quantitative or experimental data on typical dry yeast viability after X months. I’ve seen plenty of the answers of “It will be fine,” or “pitch rate calculators are unreliable for yeast viability,” or “I’ve never had a problem,” or “it probably varies by strain,” and that all is great–but those are not at all what I’m looking for.
It’s quite possible the data don’t exist or aren’t publicly available, which is a sufficient answer for me, too. I’m must hoping there might be some semi-obscure presentation or white paper (I’ll even settle for gray literature).
Thank you in advance!
Lallemand has a “best practices” PDF with some shelf life information. The direct link to the PDF is here (link) (and the landing page to the download button is here (link)).
From the PDF:
… also
… it seems to vary by strain.
eta: WRT open sachets, there was a topic over in Brewers Friend forums (link) with some ancedotal experiences. I use up open sachets within a couple of months (closed tightly with a rubber band and stored in the fridge) and haven’t noticed problems.
I’ve used dry Yeasts that have been 3 years out of date. If in doubt make a 1 litre starter and pitch, let it sit on the stir plate for 36 hours. If its viable you will get action in this time. I have also resealed out of date packets when only pitching 1/2 and they have been fine.
Cool! Those are super helpful, and I had missed them on the website. Those are the only data I’ve seen so far, so it’s cool to note the total lack of variation over 3 years.
Does refrigerating dry yeast actually make a difference?
Personally I’m not sure. I think this is a good question.
According to my sources at manufacturers, it absolutely makes a difference,.
Fermentis recommends refrigerating dry yeast for longer storage. See this guidance for US-05: “For less than 6 months: the product must be stored below 24°C. For more than 6 months: the product must be stored below 15°C. For short periods not exceeding 7 days there is an exception to these rules.” This is in line with the guidance for storing dry baking yeast from companies such as King Arthur: “For best results, store in an airtight container in the freezer for 12 months or longer.”
Fermentis has a webinar recording, " Production, Quality and Shelf life of Active Dry Yeast," that I suspect addresses this question at some point. I tried skimming the recording but it’s pretty long. Webinar recordings - Fermentis
All my info comes from direct conversations, but mirrors that info.
I’ll definitely check out the webinar! I found the YouTube recording – link here.