Lesson 6 - Yeast Propagation

Most breweries will, at some point, have to introduce a new yeast culture. This could be in the form of a laboratory slope, a pack of dried yeast, or a supply of bulk yeast. Whichever the method, a quantity of yeast sufficient for brewing and of high enough quality, must be produced. In this lesson, we discuss why this is necessary and how it is done.

In 1883, Emil Hansen, working at the Carlsberg Laboratory in Denmark, made the very first pure yeast cultures and began using them for brewing. At first, there was a great deal of scepticism, but since then, most brewers have followed his lead. For a long time, most brewers kept the process simple and just continuously cropped and re-pitched; however, the pressures of large-scale commercial brewing meant that apart from a few very traditional breweries, the majority now have to limit the number of times yeast can be re-pitched.

This means that a new culture has to be periodically introduced into the brewery. In this lesson we will examine how this process works.

It was not until the middle of the nineteenth century that scientists accepted fermentation was a natural process caused by growing yeast cells. Before then, it was thought to be just purely chemical. Early versions of the German beer purity laws had no mention of yeast because it had not been discovered. When it was, it had to be added as a beer ingredient. Medieval brewers were smart; they knew that if some of the foam from one fermentation was added to the next fermentation, the process worked a great deal better. They called this magic agent “Godisgoode”.