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So hopefully this does not seem like too silly a question...but is there anything in a typical small packet of baker's yeast aside from actual yeast organisms (S. cerevisiae)?

I guess that I always assumed that there was some kind of filler agent such as cornstarch mixed in with the yeast in order to give it some "substance". However, when looking at the ingredient list for baker's yeast on multiple manufacturers' websites, yeast is listed as the only ingredient.

I researched further to find that a single yeast organism of the species S. cerevisiae is only approximately 6 microns wide. For comparison, a grain of table salt is something on the order of 500 microns wide. So I am at a loss to understand how I am able to see individual "grains" of yeast.

So one or more of these possibilities seems to be true:

1) There is some kind of filler in the yeast packages that is simply not listed.

2) There is actually nothing but yeast organisms in the package. Even though individual grains seem discernible, this may simply be an optical illusion of sorts or a large number of yeast cells sticking together which appear to be a single grain/cell.

3) ???

All evidence seems to point to number 2 being true, but I am just trying to determine if I am correct about this. It seems counter-intuitive to me, though, that each packet contains a lump of single-celled organisms with no filler or any kind.

Please enlighten me or point out what I am missing!

Much appreciated.

5

Since you mention grains, I assume you're talking about active dry or instant yeast. The short answer is that either way, you're seeing granules of yeast plus dead yeast cells and dried growth medium, with the ratio of each depending on the type.

The Wikipedia page on Baker's yeast has plenty of detail about the various types of yeast. Notably, it lists several stages of processing:

  • cream yeast - basically just yeast siphoned off, in liquid form. It's perishable enough that you can't generally buy it.
  • compressed yeast - essentially cream yeast with most of the liquid removed, most commonly sold in the form of cake yeast. It's still perishable, but lasts long enough to sell.
  • active dry yeast - fully dried, "coarse oblong granules of yeast, with live yeast cells encapsulated in a thick jacket of dry, dead cells with some growth medium".
  • instant yeast - similar to active dry, but smaller granules and more live yeast per volume. This makes it more perishable but easier to use. (On Food and Cooking mentions that it's "in the form of small porous rods that take up water more rapidly than granules.")
  • 2
    This is good information! I think that "growth medium" was the key term that I needed to get more info since I was not aware of that term. For instance, I found this link which describes different types of growth media for this species of yeast: i-med.ac.at/hmtd/genmeth/cellmethods/docs/mediayeast.pdf I don't really understand what these growth medium ingredients consist of (such as bacto peptone, for instance), but I have enough info to read further about it Do you know a ballpark of what percentage of the product would be growth medium as opposed to actual yeast cells? – Steve Sep 27 '16 at 2:23
  • On non-organic instant yeast packets, there are often emulsifiers and similar additives listed these days. – rackandboneman Sep 27 '16 at 10:26

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