Recently we’ve worked on a method to categorize our yeast strain's alcohol tolerance level more accurately. We developed a standardized method to give brewers a more quantifiable description.
In this procedure, we use a media such as YPD and add ethanol in various percentages in a 96-well plate. Yeast is inoculated in each well at various levels, and the growth is measured on a microplate reader over 48 hours.
Below is a heatmap of our yeast strains and their growth at these alcohol levels. This has helped us determine whether they are high, med, or low-tolerant strains.
A few notes:
- A highly tolerant strain does not indicate that it will attenuate more than another strain. It only reflects the ability of yeast to endure higher concentrations of ethanol.
- The ABV values here are not the highest a strain can endure. When yeast is inoculated directly into an ethanol solution rather than producing the ethanol itself, it usually has a lower tolerance than in a fermentation.
How to interpret this heatmap:
- As the color fades from red to beige to white, the alcohol tolerance goes down.
- For example, WLP545 Belgian Strong Ale Yeast has a high ABV tolerance, whereas WLP090 San Diego Super Ale Yeast has a relatively lower one.
- This does not mean a strain cannot reach 12% or 15% ABV in fermentation. We are simply using this assay to categorize strains using quantitative data.