Lesson 5 - Clarification – Centrifugation SAQ

** Your brewery has decided to install a centrifuge due to high amounts of solids in the beer, causing quality issues and poor filtration runs. What determines a well centrifuged beer and how does this benefit the remainder of the brewing process? The brewery produces small volumes, and so speed is less of an issue. How will these quality and filtration issues be improved, and which types of centrifuge would you consider for this application?

Response:

To address the quality and filtration issues, a centrifuge is the ideal process solution to clarify and improve colloidal stability via the removal of unwanted beer components. Centrifugation removes cold break, which contains polyphenol protein complexes and causes haze in the final pack if it is not removed. It also reduces the solids loading on the filter to improve filter run lengths, helping to maintain good filter bed permeability. Cold break also contains fatty acids, and again, effective removal will promote foam stability and improve the presentation of beer in glass.

When it comes to selecting a centrifuge, a brewer has the option of two main types of technologies; these are the self-cleaning clarifiers and decanter clarifiers.

• Self-cleaning centrifuges are also called disc-stack centrifuges and operate with low solids contents, typically up to 30% solids, and are located between the fermentation to maturation tank where they process the whole vessel. These centrifuges do not operate well when the solid content is high, such as vessel or tank bottoms with high amounts of yeast.

Disc-stack centrifuges can run at a range of speeds, and this is dictated by the solid content of the beer at the inlet. Typically, the higher the solids content, the slower the rate of operation. The yeast and solid material are removed via a mechanism where the spinning bowl rapidly opens, and the solid sludge is ejected into a discharge system. There are advanced set-ups available which include an automated ‘self-thinker’ control system, to monitor inlet turbidity and define the exact time to eject the bowl. These centrifuges run most efficiently when they receive a steady stream of uniform concentrations of solids in the liquid feed, and this will be the deciding factor on whether this centrifuge type would be appropriate for this application.

• However, decanter centrifuges are used for applications with higher loading, where solid levels may be up to 60%. The main design difference in comparison to a disc-stack centrifuge is the design. A decanter operates via a rotating screw housed within a casing, which discharges solids at one end and processed liquid discharges at the opposite end. Due to the higher solids loading, these centrifuges operate at a lower speed. This application may be more appropriate as there is a greater solid loading capability of a decanter centrifuge, and in addition, no requirement for dilution of tank bottoms before processing.