Lesson 8 - Materials of Construction End of Unit SAQ
This lesson allows you to test yourself on the material covered in the lesson on Materials of Construction and to determine the level to which you have met the learning outcomes.
Suggested Response - Q4
***You have been asked by the owner of a small brewery to make a recommendation on the material for a 150 L fermenter. The owner has been able to find suppliers of a high-density polyethylene tank and an SS304L tank. What advice would you give the owner?
Response:
Firstly, let us consider what the requirements for a fermenter are:
-
Strength – at 150 L, the required tank size is reasonably small. The material does not need high strength, as is the case for a large fermenter.
-
Hardness – ability to withstand manual cleaning if required.
-
Formability – the tank must be easily formed into its shape.
-
Corrosion resistance – the tank has to withstand beer, cleaning liquids (such as dilute caustic and acid) and sterilants.
-
Hygiene – the surface must be hygienic, food grade, not taint the product in any way, and be easily cleanable.
-
Temperature range – depending on the cooling medium used minimum temperatures should be no lower than -10 °C. Maximum temperatures depend on the type of fermentation but should not normally exceed 30 °C.
-
Thermal conductivity – Fermenters are normally jacketed, and cooling is applied. However, given the size of the vessel, it could even be put in a cold room or have internal coils or cooling plates. Therefore, adequate thermal conductivity is required, but it does not have to be excellent.
-
Price – This depends on the budget. The question to the owner is what budget is available?
-
Longevity – It depends on how long the tank is required to last. The question to the owner is whether this is a long-term investment or if he/she plans to upgrade in the near future.
Let us now compare the two materials based on these properties:
|
|
HDPE |
Stainless Steel SS304 |
|
Strength |
Medium but adequate in this size. Would not be suitable for much larger vessels. |
High. For this size tank the material could be thin. |
|
Hardness |
Relatively soft. |
Hard and scratch resistant. |
|
Formability |
Can be formed, more specifically it can be rotary moulded which is how most tanks are made. |
Can be formed and welded. |
|
Corrosion Resistance |
Good for the duty. |
Excellent for the duty. |
|
Hygiene |
Needs to be food grade certified. |
Hygienic material if it is smooth. |
|
Temperature Range |
Can handle these temperatures. |
Can handle a much larger range but it is not required. |
|
Thermal conductivity |
Low |
Medium to High |
|
Price |
Low |
High |
|
Longevity |
Medium |
High |
In summary, stainless steel would present a more durable long-lasting option and offer superior performance in all aspects. However, the price can be a determining factor, and therefore, the recommendation would be for an SS304 if the owner can afford it. The HDPE can, however, be used as a fermenter as it meets the basic requirements.