Lesson 6 - Design of Fermentation Vessels
This unit began with the principles that underpin fermentation. This lesson now explores how these are put into practice. It covers how fermentation vessels must be designed to suit the behaviour of the yeast strain being used, as well as the nature, scale, and sophistication of the processes available.
Preface
Fermentation plays a key role in the brewing process. This lesson moves on from the theory of what happens when yeast grows on wort and makes beer, and looks at the design, operation, and control of the vessels and associated plant that are required to make it happen.
Requirements of fermentation systems
We begin with the essential features of fermentation systems:
-
Microbiology. From a spoilage perspective, fermentation is a high-risk part of the brewing process. We start off with uninoculated warm oxygenated wort so the fermentation vessel must address the risks of contamination. This includes managing the risks during filling, pitching, active fermentation, cropping, and beer removal.
-
Cleanability. Vessels must be cleanable in terms of removing taints and eliminating the risk of microbial spoilage. The costs of cleaning operations are obviously also important and so the sophistication of the methods used must match that of the plant.
-
Yeast management. Fermenter design has to be suited to all the process steps listed in point 1, above. Most important are pitching and cropping. It is important that yeast is properly dispersed at the start of and during active fermentation. At the end of fermentation, the method of cropping must match the behaviour of the yeast.
-
Temperature control. All fermentations need cooling to maintain the desired temperature. Cooling capacity must enable the chosen temperature to be maintained at all stages in the process from primary fermentation to emptying.
-
CO2. We might want to collect CO2 formed in fermentation and if so we need a way to do this. If we do not collect it, we must have a method for dispersing it safely since CO2 is toxic at concentrations greater than 1% v/v.
-
Monitoring progress. We need a method of removing samples to measure gravity and possibly vicinal diketones (VDK) to make sure that the fermentation is proceeding satisfactorily.
-
Capacity. Fermentation vessels must be big enough and of a sufficient number to meet the needs of the rest of the brewery.