No, we’re not talking about the new series of Gladiators (although we confess it’s our guilty pleasure…!) We’re talking about the choice of steels we give for our Dominator depackaging machine and the question we often get asked: “why would I chose stainless steel over mild steel?”
Let’s be upfront, stainless steel is more expensive, so it is a worthwhile consideration when you are considering your return on investment and value for money over the long-term. Whilst we can’t be conclusive on your specific needs (sorry, that’s for you to decide!) we can share our experience and what we would recommend you think about when selecting your material.
Are you processing food waste?
The question of which steel becomes most relevant when processing food waste – be that municipal, residential or commercial, and being depackaged for animal feed, composting or anaerobic digestion purposes.
Food waste can be corrosive. Just how corrosive depends on the pH of the surrounding environment but as a general rule, food waste has acidic properties as follows:
- Fruits and Vegetables: Highly acidic, with pH values between 3.0 and 5.0 (e.g., citrus fruits, tomatoes, and fermented foods).
- Dairy Products: Slightly acidic to neutral, typically around 4.5 to 6.5.
- Cooked Grains and Breads: Usually near neutral or slightly acidic, ranging from 5.0 to 6.5.
- Meat and Fish: Slightly acidic to near neutral, generally 5.5 to 7.0.
- Coffee Grounds: Fairly acidic, around 4.5 to 5.5.
A simpler rule of thumb can be to consider the wetness of the waste, where we see dry produce such as grains and breads cause less corrosion. The advantage of stainless steel is that it resists such corrosion, extending the lifetime of your machine.
Are you involved in food production?
Sometimes, the processing of food takes place to produce new food – i.e. it’s going back into food system for either animal or human consumption. In this scenario, the relevant regulations around food safety must be reviewed and applied, which may specify that all contact services need to be stainless steel.
Biogas quality and yields.
If you are depackaging organic matter for the purpose of anaerobic digestion, you may find that different pH levels yield better results in terms of your biogas efficacy and/or the efficiency of it’s production. Some AD plants may therefore wish to intervene and balance the acidity of the matter before processing and in this scenario the resultant pH level is worthy of consideration.
In summary
Consider what you will be processing now, and potentially in the future. What acidity levels do you expect to process and how may this change. Whilst stainless steel is a more expensive upfront investment, for more acidic produce it is likely to deliver an improved lifetime value.
Footnote: It is the responsibility of the purchaser to select and order the correct steel for their needs. The purpose of this article is to share our general observations and is not intended to give advice or guidance on (and therefore will not incur any liability in relation to) any specific project.