Where can I buy live yeast? Who sells it? Can I buy it non-commercially? Does anyone sell it online?
I've found it difficult to find, at least in the United States's grocery stores.
Another option-- if it is available to you-- is a grocery store in an area with significant population of recent Eastern European immigrants. There was a Polish store in Ann Arbor, MI (until it closed last year) where the live yeast was available by weight (cut from a big block, of the same consistency as cake yeast).
Both Red Star and Fleischmann's produce fresh cake yeast, but as it is a perishable item with a limites shelf life and a need for constant refrigeration, they limit their sales area and state so on their websites:
This traditional form of yeast is found in the refrigerated section of the grocery store. Due to its short shelf life, it is available in limited areas only.
Cake Yeast is available in limited markets in the midwest and northeastern U.S.
If you happen to live in those states, remember that fresh yeast needs refrigeration, so it will not be in the baking isle with other dry yeast types, but in somewhere in the refrigerators. Ask the shop assistants.
Some users in other forums report that, according to their observation, some stores stock fresh yeast during typical baking seasons like Christmas, but not during the rest of the year. I can not comment on the correctness of that claim, but as I read it in various places, there might be a grain of truth in it. Even stores "in the fresh yeast area" are taking a small financial risk stocking it - it's perishable and the standard consumer buys the dry yeast they are familiar with.
If you are out of luck (geographically speaking) I suggest keeping your eyes open for small ethnic or artisan bakeries. Fresh yeast is available in larger units. If you find a bakery using it, asking very nicely might get you the desired ounce or so. Note the conversion rate - you will need about 3x the amount of dry yeast by (weight).
Buying fresh yeast online is probably a futile attempt - where the manufacturers refrain from shipping truckloads of the stuff, an online retailer would have to go through an unreasonable amount of trouble to ship 2oz yeast and keeping it cool while doing so.
Try a homebrewer's supply store, or ask at a local bakery if you can buy some of theirs off of them, or (even better/cheaper) you could make your own sourdough starter.
For those who have said that dry yeast is the same as fresh yeast: it depends upon the recipe. I have my grandmother's recipe for Refrigerator Rolls. I'm 62 and the recipe is much older than me. I have tried dry yeast in this recipe and it just plain doesn't work. Someone even gave me some instructions to adjust the recipe and it still didn't work. So, every year I go on the hunt to find my fresh yeast. I have found though that you can freeze it, right away, and it keeps a while longer. But, once you thaw it you have to use it right away. I have found it at some Giant Eagle stores. Mina
Yeast is actually everywhere, so you don't need to buy it. Just buy some wheat berries, grind it up (or use whole wheat flour), mix it with spring water and sooner or later you get "yeast." Keep it in the fridge, water it regularly and feed it regularly with fresh flour (discarding a portion of the levain to make room). I guarantee you that this will produce the finest bread you've ever eaten. And no, it won't be sour.
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