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 - Q4
** You use a moderately flocculent lager yeast to brew your beers. Recently, you have noticed that the solids concentration of your bottom crops has significantly decreased. Furthermore, the green beer yeast count is higher than normal. What investigations would you conduct to determine what has caused this change?
Response:
This question requires you to take a logical approach to solving a problem that could have several causes. There is, however, a clue that could point you in the right direction. This clue is the word ‘flocculence’.
There is another clue. The question implies that the observed change in fermentation behaviour is not limited to a single fermentation but applies to all current fermentations using that yeast. It does mention “beers” and so more than one wort quality could be involved but only one yeast strain.
If the solids concentration of the yeast bottom crop has changed, this suggests that yeast flocculation might be causing these changes.
This should lead you to two basic questions:
i) Have the process conditions altered in any way that might influence how well (or not) the yeast crop forms?
ii) Has the yeast itself changed?
Let us consider fermentation conditions first. Assuming that important parameters such as time taken to attenuate and degree of attenuation have not changed (and the question does not say otherwise), it seems unlikely that the process conditions have altered significantly enough to cause a change. A change in water treatment or brewhouse practices could possibly have caused the Ca2+ ion concentration to be lower than normal, which could result in poor flocculation. In this instance, this should be investigated and either rectified or eliminated as a cause.
With regard to the yeast, we should first check that we have been using the correct strain. To do this, we must investigate the brewery’s yeast supply system, which should indicate whether or not this is a possibility. If any doubt arises, we should then check the yeast strain’s identity, preferably using a genetic approach.
If the strain identity is OK, we should then check to see if the strain’s flocculence character has changed. Changes in this property do occur via mutation.