Lesson 3 - Yeast Morphology and Evaluation SAQ
This lesson allows you to test yourself on the material covered in the Yeast Morphology and Evaluation lesson, and determine the level to which you have met the learning outcomes.
Suggested Response - Q5
*Brewing yeast are mesophilic, heterotrophic facultative anaerobes. What do these terms mean?
Response:
This appears to be a complicated question, so let us consider each term in turn:
Mesophilic refers to the range of temperatures over which the cells can grow. In the case of brewing yeast, these are in the medium range (meso = middle; phile = liking). Although there are differences between ale and lager yeast strains, the range is roughly 10-40°C.
Heterotrophic means that brewing yeast require a source of relatively complex chemical nutrients for growth. “Hetero” means different, and “trophic” refers to nutrition. This describes brewing yeast’s ability to use a wide variety of nutrients, both organic and inorganic. This applies to brewing, as we use wort as the growth medium. As you know, wort is a complex mixture of compounds, largely derived from natural materials such as malted barley.
A facultative anaerobe simply describes an organism that usually grows best when oxygen is present but can, under the correct conditions, grow in the absence of oxygen.