Lesson 4 - Clarification – Centrifugation
This lesson discusses beer clarification via centrifugation. Clarification removes yeast and solid particles from the beer in order to make it ‘bright’ or reduce the amount of haze. Centrifugation is one method that we can use to clarify beer. This lesson looks closely at the physics of centrifugation and the concept of accelerated gravitational force. By the end of the lesson, you should understand the importance of this process and its impact on final beer quality.
Advantages and Disadvantages of Using Centrifuges
Not all breweries use centrifuges, so what are the advantages and disadvantages of using them?
Let us start with the advantages:
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Centrifuges help improve filtration performance by reducing the solid loading in beer. Long filter runs are essential to meet filtration operating costs and ensure the filtration system consistently delivers volume requirements to its design capacity.
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Centrifuges have small space requirements.
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Centrifuges are designed to facilitate CIP and be sterilised effectively.
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They are hermetically sealed by fitting seals on all moving parts, to avoid oxygen ingress.
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Filter aids are not required, neither is absorption.
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When at full speed and the solid loading is consistent, a centrifuge can run for very long periods of time.
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Rapid and efficient clarification before further processing steps.
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It achieves a consistent clarity.
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The centrifuge process can concentrate solids to 13-25% dry matter.
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Low beer loss in comparison to natural sedimentation.
But at the expense of what? Here are some disadvantages:
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Initial capital cost for installation is high.
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It has a high electrical demand.
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Large motors are required to meet the very high inertia generated by the centrifuges’ rotating parts, for example, a centrifuge running at 200 hL/h would need a 22.5 kW motor.
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Centrifuges are noisy! As mentioned before, they require a dedicated room; ear protection must be worn when in the vicinity. The major downside is that this may deter people from inspecting it. This in turn could mean that faults and issues are identified and remedied more slowly than they should be.
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Centrifuges are complex. They require specialist maintenance and parts can be expensive, leading to overall high maintenance costs.
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Centrifuges create much heat due to the high number of revolutions per minute. This causes beer temperature pick-up, up to 3-5°C. This means that we will need a beer chiller in order to cool the beer after centrifugation. Higher temperatures at the maturation phase can impact beer quality and negatively affect the final colloidal stability by breaking apart haze forming particles (proteins – polyphenols). This increases the risk of permanent haze formation in the final product, as the haze forming particles create stronger bonds when they re-join. Higher temperatures can also result in CO2 loss in the beer, as carbon dioxide is less soluble at higher temperatures. This will require increased carbonation post filtration to achieve brand CO2 specification.
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Shear forces generated by the centrifuge can negatively impact yeast vitality and physiology. This makes the yeast less suitable for re-pitching than yeast cropped directly from the vessel.
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The mechanical break-up of large particles due to shear forces may increase the concentration of fine haze particles. β-Glucans can unfold and reform as gums or jelly-like substances on the filter, which shortens filter run lengths.
With these advantages and disadvantages in mind, what are the most important factors to consider when controlling quality in a centrifuge operation?
Oxygen exclusion – a brewer should ensure seals are well maintained to create a hermetically sealed process that avoids any risk of oxidation.
Clean and sterile environment – a brewer should ensure brewing standards and CIP regimes are adhered to, to avoid the risk of microbiological contamination.
Minimal beer temperature rise – a brewer should maintain a constant feed of beer onto the centrifuge to minimise temperature pick-up. Repeated stop and start scenarios also cause the beer’s temperature to increase.
You want to install a disc-stacked (self-cleaning) centrifuge in your brewery between the fermentation and maturation vessels. This will improve your process time and reduce yeast loading on your filter. How will you integrate it into your existing operation? What do you need to consider when planning this?
Give yourself 5-10 minutes to identify some potential solutions and consider the merits of these options. Then click ‘Next’ to continue with this lesson.