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Current State

Currently I have designed a coffee roaster that mostly uses the stainless steel tri clamps / tubes that many brewers use. The system can get up to 450 degrees F (232°C) even with moving air.

Question

I was wondering if someone has come across a cheaper material or system than the tri clamp one? The requirements are to withstand 450 degrees F (232°C) or more, and to be food safe. Current material is stainless steel which works for food safe but the pipes with all the clamps are up to $300 or so which is more than the rest of the project.

What I have investigated so far

I looked at many plastics available and while some can handle higher heats, those are generally more expensive. I also looked at using HVAC ducting but learned that galvanized steel can let off gasses when heated up. So are the stainless steel tri clamps the best solution for the money or is there something cheaper out there that I am not thinking of?

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  • $\begingroup$ You write "the system can get up to 232°C" - what is the hottest the part we are talking about can possibly reach? $\endgroup$
    – mart
    Aug 18, 2020 at 19:12
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    $\begingroup$ @mart "What is the hottest part we are talking about can possibly reach?" 232 C $\endgroup$
    – Eric F
    Aug 18, 2020 at 19:42
  • $\begingroup$ I think I completely misunderstood your question: Are you looking for a vessel, or are you looking for a system analogous to the tri-clamp, to fit parts together? $\endgroup$
    – mart
    Aug 19, 2020 at 6:44

3 Answers 3

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In the food industry not many materials are used because of strict policies. The mostly used ones are definitely stainless steels (AISI304/316 and the even better AISI316/L). The other common material is nylon. For applications where only food contact is required(ie containers mostly) also BOPP or other polyolefins are used but they are not common in food processing.

In your case stainless steel is probably the best choice in terms of thermal stability, food safety and also from an esthetics point of view. I would say that PA66(high grade nylon) could make it but you’d be really at the edge of the service limit, I wouldn’t use it before good testing for the thermal aspects.

Would PA66 be better then stainless? Well it might be cheaper but machining is more complex then with stainless and might costs more. I wouldn’t consider 3D printed nylon because of too low properties.

The only other options for food safety is ceramics, this is feasible if you are not using any elastic behavior of the material. One other point is that it will fail in a brittle manner not ductile like steel. In the other hand this could be 3D printed and still capable of withstanding the environment you have. It depends on how many parts you’re looking to build.

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    $\begingroup$ A great answer and exactly what I was looking for. The PA66 is interesting to investigate as well. Thanks! Interestingly I found that buying stainless steel tubes with the Tri clamp ends already welded on are often cheaper than stainless steel tubes in bulk which I think is just supply and demand working in this case. $\endgroup$
    – Eric F
    Aug 19, 2020 at 12:57
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I suggest investigating copper. Copper has historically been used for coffee rosters. Copper is food safe, provided the food in question is not acidic - pH should be > 6. Otherwise copper would dissolve, copper is a heavy metal with some toxicity.

Coffee - the drink - is actually more acidic than that, however in roasting you won'ty have an aquaous phase for the copper to dissolve into.

The big advantage of copper is that you can replace welds with soldered connections. In your case, you need to hard-solder the copper - using a solder with a liquidus temperature > 450°C. Look for a solder that is declared safe for drinking water applications. Soldering is generally easier and cheaper than welding, especially stainless steel.

Coffee roasters made from copper are still being sold, you should be able to find out if the acidity of the coffee actually poses a problem.

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  • $\begingroup$ I think the usage of copper would require extensive research, I am not sure it complies with actual food safety standard. Copper pots are not sold anymore, at least in Europe as far as I know. Those that are sold are made of copper but plated often with silver on the inside touching the food $\endgroup$
    – Alberto Brambilla
    Aug 19, 2020 at 6:16
  • $\begingroup$ I actually hadn't thought of copper. I will do a bit of research on this. Thanks for the answer! $\endgroup$
    – Eric F
    Aug 19, 2020 at 12:58
  • $\begingroup$ Seems it is incredibly controversial if copper is safe or not with food. We as people can consume small amounts and be ok so kind of a gray area. Either way for the sake of the question this is a good answer. $\endgroup$
    – Eric F
    Aug 19, 2020 at 13:02
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    $\begingroup$ I would definitly advise against copper in any cooking application but in a dry case it cold be ok. As Alberto pointed out copper is often plated with silver or (I think more often) zinc, this too could be an approach. $\endgroup$
    – mart
    Aug 19, 2020 at 13:13
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    $\begingroup$ I should add that you can solder stainless too, one less point in favor of copper tbh $\endgroup$
    – mart
    Aug 19, 2020 at 13:27
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I suggest aluminum: able to take temperatures long term and at stress up to 600 F, cheap, strong, very machinable, readily available, and food grade.

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