Yeast

We have our own indiv idual strain of brewing yeast, which produces the unique flavours of our beer that we like so much. Yeast is a single-celled f ungus called Saccharomyces cerevisiae from the Latin: ‘sugar fungus of beer’. Those Romans knew a thing or two!

We spend a considerable amount of time and effort looking after our yeast and making sure it performs as we want. But at the end of the day it’s a living thing so may not do as we would like! Why yeast should produce alcohol in the manner it does is quite interesting. Yeast can derive its energy anaerobically (without oxygen) by breaking down sugars into alcohol and carbon dioxide. In terms of energy this is not very efficient, but nature is pretty clever.

The alcohol that yeast produces acts as a poison to other micro-organisms such as bacteria and moulds which would normally compete f or the food source. Once the yeast has produced the alcohol it can then use oxygen to break it down to acetaldehyde thus releasing a lot of energy. So effectively it produces a poison and then feeds on it! The brewer can also take advantage of this trick by keeping the oxygen (or air) away from the beer after fermentation. This way the alcohol protects the beer from infection and the yeast cannot break it down without oxygen.

With traditional cask beer this is the only preservation of the product, there is no pasteurisation or other treatment used. However, once the cask is opened and the beer dispensed then air will enter allowing the yeast to start to break down the alcohol. This is one of he reasons why beer will go ‘off’ quite quickly once the cask has been opened