Actually we do know. IDY, ADY, or fresh, it's all the same thing in terms of the strain - as you mentioned, the differences are in the way it's preserved and how much inert material is present. These are all saccharomyces cerevisiae. There is supposed to be zero advantage to using ADY, and as I understand it, the only reason it's still being produced is that it's older and some folks are set in their way and want to keep using what they've used in the past. Fresh has much more water in it, so it's supposed to be easier to measure out accurately in smaller quantities for commercial use and consistency purposes, but beyond this, I'm unsure that there is any advantage - perhaps a fresh yeast that's always used within 2-3 days of purchase will have a more consistent active component versus IDY that's stored for a year and used anywhere from 1 day old to 365 days or more old - I'm unsure. ...but given the fact that whatever amount of yeast you put into your dough will start to multiply after only a short amount of lag time and that the multiplication is greatly affected by small differences in temperature, I can't see how even minor differences in the actual number of active yeast cells you start with will matter more than if your room temperature is 20C or 21C or if you mix to 23C or 24C.
Is that something that Fleischmann has said, or no?
Because i used to homebrew beer, and while it's mostly Saccharomyces cerevisiae, the properties of specific strains of S.c vary far and wide.
There are more commercially produced strains of S.c than you can shake a stick at, and the differences between them range from subtle to striking. Not even considering lager yeast (Saccharomyces pastorianus) for people who like their beer super mild and Brettanomyces bruxellensis for the people who like really challenging beers -- literally isolated in a search for the cause of spoilage in British beer.
Wine yeasts are also in the S.c family but most of them can't efficiently consume the maltose in beer wort. And then there's Lalvin's EC-1118, which comes out of the packet unable to eat maltose efficiently but will adapt to it in just a few hours.
Generally speaking yeast produces alcohol and co2 but also produces other products which are referred to as 'congeners' -- and generally speaking, they produce more congeners when they are stressed, which is to say when they are operating outside of the parameters that they are adapted to.
For most of your ale yeasts you get the most neutral performance at temperatures between 50-65f. Lager yeasts (S.pastorianus) prefer cooler temperatures.
I think it's generally suggested that bread yeasts may produce congeners that are pleasing at warmer temperatures.
The strains of S.c that are favored for wheat beers turn out to produce a lot of esters and phenols when stressed, and some brewers produce "banana bread" beers by fermenting with wheat beer yeasts at warmer temperatures. Because they produce esters similar to isoamyl acetate when stressed.
Beer yeasts, wine yeasts, and distiller's yeasts don't make bread well at all. And bread yeast makes pretty awful hooch.
So, unless the major bread yeast vendors admit that their active and instant yeasts are the same thing with different preservation, I will have to consider the possibility that they aren't. Though that would be more expensive.
