Lesson 4 - Wort Cooling and Oxygenation Technology

As brewers, we must consider the importance of oxygen to our yeast, and its subsequent fermentation performance. This is still an under-estimated parameter in some breweries. Let us look at this seemingly under-estimated fermentation input parameter a little more closely.

Yeast requires oxygen to make unsaturated fatty acids and sterols (ergosterol in particular) as a key component of cell membranes. This occurs at the start of fermentation. The yeast requires cell membrane material to reproduce via a particular form of mitosis. We call this ‘budding’. We also call this multiplication of cells ‘yeast growth’ e.g. an exponential increase in population. Yeast synthesises these compounds as our wort generally has a limited amount of these essential lipids. The fixed amount of oxygen thus produces a fixed amount of cell membrane material synthesis. This in turn promotes a fixed amount of cell growth. This highlights how critical the exact amount of oxygen addition is to our brewing process.

This is a lot of science and microbiology to digest.  However, it explains why this parameter is often under-estimated. The degree of its impact on our brewing process may not always be fully appreciated. In short, the amount of oxygen we add will determine the amount of yeast growth; this plays a very large part in our brand profile.

We must note that it is very difficult to accurately measure these lipid compounds in the yeast cells. It is a lot easier and quicker (in real time) to measure and monitor the amount of oxygen that we give to the yeast. This will achieve the specific amount of growth (lipid synthesis) needed to create the required degree of fermentation.

The absence of adequate oxygen levels, and the resulting lower amounts of these essential growth compounds, can cause the following problems:

• Sluggish fermentations – with poor beer flavour.
• Hanging fermentations – failing to attenuate to required degree.
• Poor yeast growth – inadequate number of yeast cells to complete fermentation. 
• Poor yeast health – yeast not suitable for reuse. 
• Increased microbial contamination – insufficient yeast activity leaves beer at greater risk of microbiological infection.