Lydia,
My starting point with yeast is almost always with weight, which I usually end up converting to volumes because of the small amounts used. Hence, I have little reason or occasion to read what the yeast producers put on their yeast envelopes and little bottles. Since I use primarily instant dry yeast (IDY) and have been operating out of a one-pound bag for several years, I have even less reason to pay attention to yeast labels.
That said, I believe if you look at the information on yeast packages, no matter what is inside--ADY, IDY, bread machine, Rapid Rise, Quick Rise, etc.--the information is almost always the same. That is, 1 envelope = 1/4 oz. = 7 g. = 2 1/4 t.--which is what your first statement says. Hodgson Mills is a little bit different from the others in that its ADY packets include 5/16 oz., or 8.75 g. Fleischmann's and SAF tend to correlate their dry yeasts with 0.6 oz. fresh yeast, whereas Red Star correlates with 2 oz. of fresh yeast, quite possibly because that may be their standard package size for fresh yeast. Red Star also correlates three 1/4 oz. packets with 2 oz. of fresh yeast. Fresh yeast is a moot issue with me in any event because no one around me sells it anymore.
What is significant is that the yeast producers do not correlate ADY with IDY for their consumer markets. I suspect this is done because the average consumer does not want to be bothered with doing mathematical conversions to determine how to convert from one form of yeast to another, and in small quantities it may not matter if the amounts are off a bit. Similar parallels exist between the amounts of regular salt and Kosher salt to use. None of this has ever been an impediment for me. I have memorized that to convert from fresh yeast to ADY, I use one half of the weight of the fresh yeast, and to convert from fresh yeast to IDY, I use one third of the weight of the fresh yeast. These conversions are not absolutely precise and it is for this reason that I often refer readers to the yeast conversion table at theartisan.net, which I understand to be exact. Once I have the weights of either ADY or IDY, I use simple conversion data to convert the weights to volumes. Using this approach, I will not get the same results as I would by following the conversion data on the consumer yeast packaging materials you referenced in your various statements. Working with weights and baker's percents as I do, I guess I've trained myself to think more like a baker than anything else.
So, Lydia, I can't tell you that your statements are incorrect. I am just following a different system that I suspect has its origins in the professional ranks of bakers, where the distinctions between the different kinds of yeast, especially in the batch sizes and quantities that they use, have greater relevance.
As far as shelf life of fresh yeast is concerned, it's moot for me at the moment since I can't find it even if I wanted it, which I don't, and I tend to be somewhat suspicious in any event of manufacturers' "use by" or "sell by" dates. It is true that one should keep the yeast refrigerated when not actually being used, and it should be used within a reasonable time because it is highly perishable. I suspect that one can use fresh yeast for a reasonable period of its "sell date" since otherwise one would be buying essentially dead yeast. Most instructions caution against freezing fresh yeast, but I have done so and found the yeast still viable when I later defrosted it and used it.
Peter
