Lesson 5 - Types of microorganisms SAQ
This lesson enables you to test yourself on the material covered in the Types of Microorganisms lesson, and determine to what level you have attained the outcomes.
Suggested Response - Q3
**Answer BOTH parts of this question:
a) Explain why Obesumbacterium proteus (Hafnia protea) is able to survive and eventually proliferate in traditional English ales.
b) Why is their presence a concern as a contaminant in brewing?
Response:
a) O. proteus is a member of the Enterobacteriaceae, related to E. coli, and so is referred to as a coliform. It is a facultative anaerobe meaning it can grow both with and without oxygen.
Traditional ale production uses top fermenting yeast, which rises to the surface of the fermenting wort. O. Proteus is able to associate with the yeast cells and survive in the yeast layer forming on the top of the rectangular fermenter.
The yeast is manually skimmed off the surface, stored, and repitched into the successive brew.
When this process is followed in successive fermentations, O. proteus is able grow and proliferate to a point where it can compete with brewing yeast, forming DMS and other products, thereby giving the beer a parsnip-like flavour.
b) Beer flavour spoilage by O. proteus is rare. However, a bigger concern is due to their ability to reduce nitrate to nitrite in wort. Nitrite is a precursor, together with wort amines, for formation of nitrosamines. These compounds are known carcinogens.