The other evening I did a lecture and training workshop for the folks up at This Is The Place Heritage Park. We rambled over a few subjects, but of key interest was the subject of yeast. I know I've been through this before here, but there was so much discussion and argument I thought I'd better straighten a couple of things out.
First, the pioneer understanding of yeast was quite limited, from a microbiology perspective. They didn't quite understand what it was, as evidenced by this quote from the Deseret News, November 30, 1854:
To Make Yeast: Hop yeast may be most conveniently made in the following manner: Boil a double handful of hops in a gallon of pure soft water for fifteen or twenty minutes; strain off the liquor while scalding hot; stir in wheat meal or flour till a thick batter is formed; let it stand till it becomes blood warm; add a pint of good lively fresh yeast, and stir it well; then let it stand at a place where it will keep at a temperature of about 70 degrees Fahrenheit, till it becomes perfectly light. This yeast will keep from one to two weeks, if corked tight in a clean earthen jug, and kept in a cool cellar.
In other words, they didn't seem to understand the idea of growing yeast, or that it was a living thing. In fact, they believed that yeast was a dead thing, the product of decay.
In the above quote, hops are used. In our discussion it was not entirely clear about what the hops were for. Hops are a small flower that grows on a vine like grapes. Hops have astringent qualities which deter certain kinds of detrimental bacterial growth. Hops and yeast get along quite nicely however, so the hops help to keep a yeast culture pure while it is being stored between uses. Otherwise, the yeast could be invaded by other airborne bacteria and become spoiled.
The question was raised, "where does one get yeast to begin with?" The above quote assumes that you have yeast to multiply. If you don't have yeast to begin with, you can lure yeast out of the air by leaving a sugary liquid open on the table. If you look at apples on the tree or grapes on the vine, they are covered with a dusty coating of yeast, attracted to their sweetness. You could wash the apples in water, and then feed sugar to the yeasty water, and grow a culture in this manner. Airborne yeast is naturally attracted to sweet, wherever it is found.
I believe that Mormon pioneers brought yeast cultures with them. There is some argument to the contrary, but since yeast is such a fundamental part of Anglo food culture, and since we know they had the understanding of yeast in Nauvoo, it would seem ludicrous that this knowledge didn't transfer to the Rockies.