So far I’ve discussed a few of the ways bourbon distillers manipulate the taste of their products: distilling at a lower yield (and thus a lower proof), aging at a lower proof and of course aging in new oak wood barrels. Important as those various techniques are, their impact is nothing compared to that of the most important single element in the bourbon-making process: yeast.
It’s been said that the bourbon makers of old were not so much expert distillers so much as expert cultivators of yeast. They had to be, since there was no place to buy distiller’s yeast 150 years ago. If you wanted a culture you had to grow one yourself. Normal practice was to create a slurry of malted barley and water, put it in a bowl, and leave the bowl in a fruit orchard, where fermenting yeasts were particularly abundant. (That faint white film you see on the outsides of grapes, plums and apples? Bingo).
The result was never certain. Some cultures created great bourbon, some cultures awful bourbon, so the process was one of trial and error. Once hit upon, however, a great yeast culture could make a distiller a very wealthy man. The lecturer I heard on Friday told the story of a legendary Kentucky distiller he knows who keeps a sample of his family’s yeast in his freezer at home, just in case his factory were to burn down.