Electronics > Projects, Designs, and Technical Stuff
temperature sensing a bunch of coffee beans
Etesla:
Hi all,
I've got a tricky problem that I'm not sure is even possible to resolve. Here's the issue.
To go from green fresh coffee beans to coffee, you have to roast the beans.
Roasting the beans means making them hot in a rotating drum, with the highest important temperature being around 400 F, and the lowest being room temperature.
It's nice to monitor the temperature of the beans, in order to make adjustments to the roasting process for the sake of consistency.
Normally, the temperature is just read from a thermocouple shoved into the pile of sloshing beans. Since the internal bean temperature is really the information I would like to have, the idea that a thermocouple shoved into the pile of beans will give me a good measurement doesn't sit well with me.
I was thinking that placing some sort of small wireless temperature sensor with similar thermal properties to that of a bean in WITH the beans would be a far better way to measure the internal temperature of the beans. The problem is that making a small wireless device that does this over the temperature range of interest seems impossible.
With that as background information, my question is this: How can I better estimate the internal temperature of the beans? Any ideas are welcome. Thanks.
phil from seattle:
Hmmm, it seems to me that doing what you don't like (just shoving the probe into a bunch of beans) is not that bad. The temperature that registers won't be the internal bean temperature but it should be a fairly consistent fraction of the actual temperature. I think you get there via trial and error. If you want to get more technical, you could measure the temperature drop over a period of time. Beans that haven't reached the right internal temperature will cool off faster than ones that have.
The problem of a wireless sensor is the temperature. You would need electronics and batteries that will withstand 400F.
NiHaoMike:
Drill a small hole in a bean, put a small thermocouple in it, and heat it up with a heat gun (in conditions approximating the roasting process) to get some data. Repeat with a few more beans to check for variation, and also repeat with a bean from a different batch. If you really want to be scientific, also note the size and weight of the beans used in the test, before and after roasting.
At some point, you'll be able to estimate the internal temperature in relation to the outside temperature over time. Maybe all beans of that type will be similar enough that one profile will work for all, maybe you'll have to do some size and weight measurements to tweak the process.
DrG:
I wonder how a non-contact thermal sensor might do in that situation, e.g. https://www.melexis.com/en/product/MLX90614/Digital-Plug-Play-Infrared-Thermometer-TO-Can
ejeffrey:
I'm not sure what the best approach is, but I found this paper on thermal properties of coffee beans:
https://pdfs.semanticscholar.org/1613/18efd160b933f507b45676ec24e37ffe76eb.pdf
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