I have written that Jim Beam uses 'wild yeast' and was just asked twice in as many days what I mean. Unfortunately, the term 'wild yeast' is used by different people to mean different things. In the case of Jim Beam and other 'practical distillers' of American whiskey, here is what it means.
Yeast is, of course, required for fermentation, which is how alcohol is made. Yeast eat sugar and produce alcohol, carbon dioxide, and also flavors. There are millions of different yeast strains and each produces different flavors.
To obtain a 'wild yeast' for making whiskey, a yeast maker would mix up a yeast mash from his own personal recipe, typically one taught to him by his father or uncle. The yeast mash would be a different recipe from the whiskey mash, as its purpose was to make yeast, not whiskey. He would set it in a preferred location and wait. Booker Noe told me that Jim Beam used his screened-in back porch and 'stank up the house' according to Mrs. Beam.
The yeast maker would wait until the mash began to ferment. He would then watch it, smell it, and taste it, to see if it had the qualities he preferred. If it didn't he would try again, over and over, until he got one he liked. He would then propagate it, typically keeping it cool so it would work slowly, periodically transferring some of it to fresh mash in another container, keeping it alive the way a baker does with sour dough starter. This was known as 'jug yeast' because it was kept in a sealed container that looked like an old time milk jug.
The yeast strain would be cultivated in this way and used for as long as possible, indefinitely if it made good whiskey. This was the great skill of the old time distillers, who were sometimes referred to as 'distiller and yeast maker.' Craig Beam has described to me how his grandfather, Earl Beam, taught him how to use the Heaven Hill distillery's version of the Beam family jug yeast to produce enough yeast for production. It was a three day operation that had to be done once a week. That was Craig's first lesson in distilling.
Eddie and Jimmy Russell also have told me yeast making is the distiller's most fundamental skill.
Craig and Eddie have only learned how to propagate the jug yeast for production. They haven't learned how to make yeast from scratch. I asked Craig Beam if he thought anyone today could make a good whiskey jug yeast from scratch. His answer was "maybe."