Does active dry yeast really expire?
I was cleaning out my spice cabinet and deep in the back I found two packages (e.g., six envelopes) of active dry Red Star yeast that expired in March 2009, 15 months ago as of writing this question.
With the thought that dry yeast is basically freeze-dried and should have a decent shelf life, I proofed one envelope in warm water with some sugar to see if it really "expires". It foamed right up, so it seems like the answer is, at least for one year after the marked date, no.
Although in this case, does "expired" really mean "less effective" or "will taste funny"?
If you bake a lot (yeast baking), look around for Fleischman's *Instant Yeast* in 1 pound foil bags. Yes, 1 pound. Lasts forever and it's a lot easier to use than "active dry" yeast - it goes in like a dry ingredient, and there's no proofing. A pound makes a *lot* of bread and it should cost less than $5.
@Pointy: Fleischman's Instant Yeast *is* active dry yeast. Red Star works fine too, and is available in 1lb foil bags at Costco.
No, it is not active dry yeast. It's *instant* yeast. There is definitely a difference. The Red Star yeast is also instant yeast. The names are confusing; check McGee or something.
And according to McGee, the difference is that "instant" yeast is dried a lot more quickly than "active dry" yeast, and the little particles are of a shape that absorbs water much more readily. Thus, it needs no proofing and can be added as a dry ingredient (which I've been doing for years with consistently good results).
I've used yeast that was even older than yours and although the taste of the resulting bread was fine, and it foamed up properly when tested, I found I had to use about 50% more of it to get the same density of the bread. In the end, I threw it out because it was too much trouble to experiment with it every time.
To note, yeast does expire; sort of. Cell viability goes down fairly quickly based on the age of the yeast from date of packaging: 1 month – 80% viable 2 months – 64% viable 3 months – 51% viable 4 months – 41% viable 5 months – 33% viable 6 months – 26% viable
(This should be an answer instead of a comment, but I got no rep) It really does expire, in the sense that it will be rendered totally useless, probably meaning that all yeast cells slowly died over time with humidity changes. Since I understand the difference between "best before" (loses qualities but should be harmless) and expiration date (could be harmful), I tried a best before 2006 yeast I had laying around (that's 13 years old), and sadly it didn't do a thing to the dough. I have to say the packet was cut open probably since before 2006, but whatever...