Lesson 2 - Fermentation Principles
Fermentation is critical to the whole brewing process. Achieving success at the fermentation stage involves many factors. In this lesson we look at what these fundamental factors are and the effect they have.
Point of Reflection – Reconvene
Welcome back. So, what were your thoughts?
A fermentation which stops before you expect it to could be a brewhouse (wort) issue or a fermentation control problem.
You can check this by doing a fermentation limit extract (LE) test (also known as a forced fermentation test). We take a sample of the wort, measure the gravity, and then add an excess of fresh pitching yeast. Next, we put the mixture in a flask and shake it overnight at room temperature (the shaking gets some air into it to encourage yeast activity). We then re-check the gravity. The full procedure for determining the attenuation limit of wort was covered in the Mashing Unit in Module 1 of this course.
If the gravity has not changed, it means the wort is less fermentable than it should be, which is a brewhouse problem.
If the gravity has dropped to what was originally expected, this means it is a fermentation problem. We then need to narrow this down, if we can. Issues to check are:
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Wort oxygenation and pitching rate (do the records show they were normal?)
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Failure of temperature control, with temperature lower than normal or accidental crash cooling
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Wrong yeast strain
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Selection of a much more flocculent mutant
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Premature yeast flocculation – a malt problem that causes yeast to flocculate and drop out much sooner than normal and stops the fermentation prematurely.