What is domestic yeast?
There is wild yeast, and domestic yeast. When a wild yeast has been "captured", and then domesticated by a yeast manufacturer you then have domestic yeast. There are a few different kinds of yeast, and have their differences. All yeast manufacturers start with basically the same strain of yeast, called Saccharomyces cerevisiae. It is how each manufacturer cultivates that yeast to produce their final product that differentiates one of the yeasts from another. To determine how they will do this, they look for certain characteristics that they deem desirable, then isolate those, and go on to replicate those yeast. The yeast is put on a "diet" of sorts, to train it to replicate, and then the cells when they are at a high density point, get filtered and dried. These dried cells then go on to be filtered and dried, then measured and put into packages, and head off to market. Hopefully this hub will help to make sense of some of the more prominent yeasts.
This one is dried at a much lower temperature. In this case there are about 30% of the cells that are dead. It works much faster than active dry yeast. This yeast is the one that often is preferred by those that use a bread machine for their bread making needs. It can be stored for quite a while in the freezer.
Regular instant yeast
This strain of yeast was made for more general types of baking. The tolerance for different kinds of breads is high, all except maybe the super sweeter doughs. The reason it doesn't work with a dough that contains a lot of sugar, is because it can "overdose" in a sense on sugar, and then it stops working too early. Below, are three different types of instant yeast.
Instant Yeast for sourdough and higher sugar breads
This yeast is the one for you, if you are making a higher sugar bread, or a sourdough bread. This particular strain of yeast, was actually developed just for more sweet, or very acid doughs. Instant yeast grows at a slower and more even rate even in a high acid or sweet environment. Sourdough bread is one I hope to make sooner than later. I have always wanted to try it.
Rapid Rise Yeast
This yeast has it pluses and minuses. It is made to work fast, but then die fast. It was to help out the cook in a hurry, though the final product itself sometimes suffered a bit compared to some other yeasts. It still works well, for its purposes. Bread develops a great taste or not, depending on a rather slow period of fermentation. If you cut that process short as a time saver, you may not have as good of a bread as you would have liked.
Cake or compressed yeast
This is the yeast that many of our mothers and grandmothers used in their baking. It was the original domestic yeast. It was moist, and had a kind of mushroom color, and had a clay like texture to it. Today, many commercial bakers still use it. This yeast will last about a week, if you keep it refrigerated and in a air tight container.
Active dry yeast
This is a live yeast and the process kills up to 70 percent of the yeast cells. I found it rather interesting, that the cells that died seem to surround the live ones, which acts like a barrier and protector of the live yeast cells. How interesting that is. When you add the warm water, you are proofing the dry yeast. This was developed just before World War II so the troops could have fresh bread.