Lesson 9 - Clarification – Filtration SAQ
This lesson allows you to test yourself on the material covered in the Clarification – Filtration lesson, and determine the level to which you have met the learning outcomes.
Suggested Response - Q5
**Which of the following filtration variables effect filter run length?
a) Beer flow rate
b) Oxygen content
c) Bed depth
d) Beer temperature
Response:
a) Yes – beer flow rate does effective filter length. Based on the differential pressure calculation, the flow rate of beer per unit filter area directly impacts filter performance and run length. The greater the flow rate, the lower the run length as the ∆P would increase more rapidly during the filter run.
b) Oxygen content does not directly affect the filter run length but will be a reason to stop the filter prematurely if the beer supply from the maturation tank is elevated. High dissolved oxygen will cause flavour instability by creating staling flavours. This will alter the beers’ sensory profile and reduce the brewery-fresh character. It will also require the beer to be re-worked in bright beer tank to displace the oxygen, again causing avoidable downtime.
c) Yes – bed depth does effect filter length. Similar to the beer flow rate, again based on the differential pressure calculation, the bed depth impacts filter performance and run length. The filter bed will become less permeable as the thickness increases, directly impacting ∆P.
d) Beer temperature does not directly affect filter performance. High-temperature pre-filtration will cause dissociation of protein-polyphenol complexes, however. This is a serious quality risk, and therefore, as with elevated oxygen, a filter run will stop to resolve the cooling issue.