Does rust on burrs even matter as far as grinder performance, coffee flavour, or even health risks?
I've been having an very anxious week and the weirdest shit is getting to me, so I gotta' ask. Some wet/damp beans went into my new Aergrind earlier today, which has only grinded about 12oz of beans over a week and a half (so, I'm not sure how much of that oily "protective coating" has developed on the burrs).
Since then, I've become obsessed with the idea of rust developing on the burrs. Can't even see the Aergrind's burrs clearly, so I can't confirm one way or the other.
Then I found this from Baratza's website: "Rusty Burrs - Really?". Noted in that article is the following:
"you may find some rust when you receive your burrs. Yes, this is normal and it will not harm you, nor does it make for an inferior burr."
I'm assuming this applies to other grinders, including the Aergrind.
If this is true, why are many coffee connoisseurs (i.e., not me; I'm an utter amateur) so fastidious about not getting water on the burrs like it'll be the end of the equipment or something terrible will happen?
The same article also cites the following:
The National Institute of Occupational Safety and Health (NIOSH) indicates that rust is not toxic…… If eaten, the acid in the digestive processes will convert rust to iron needed for blood formation or excrete the excess.”
Then again, rust is an iron oxide, and you can get sick from iron overdose, but correct me if I'm wrong, that would be pretty nearly impossible just from rusty burrs regardless of how many beans you're grinding, right?
So, as far as ingesting coffee that's been ground up via a rusty burr, are there any actual -- and significant/meaningful -- downsides?
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At the time I am writing this comment your question was voted down to 0. That's weird to me because you bring up an interesting question. Sorry I can't give an interesting answer but I can attempt a banal one.
As you know steel burrs are made with high carbon steel. This is harder than stainless and so is sharper and will hold that sharp edge longer. Great stuff for grinder burrs but it is rust prone. It is so rust prone that it can start rusting just by being exposed to a humid environment. Which is why Baratza notes that "you may find some rust when you receive your burrs" and why gun owners religiously clean their weapon and protect it with oil. Rust happens baby...
In the short term this rust is really just a surface stain. Its only the very top iron molecules that have rusted so it's not yet damaging your burrs. But over time that rust can sink deep and begin to corrode the steel. Preventing exposure to moisture is the best way to prevent rust. Which is why grinder owners are fastidious about not getting their burrs wet; rust is corrosive and damaging to steel.
To prevent rust an iron or steel item can be painted, galvanized or one can apply a barrier coat of oil. In the case of grinder burrs the oils from the coffee actually provide this barrier coat. As long as the grinder is regularly used, and not exposed to water, those burrs remain rust free.
As for any rust one might find on new burrs, this gets worn off quite quickly by simply grinding beans. The beans act as an abrasive to remove the rust like sand paper. If one is using the grinder regularly the rust won't come back.
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Interesting. So, if these damp beans that went into my fairly new grinder did cause rust, it's quite likely that future use will sand away said rust?
Thanks for seeing some value in my question. I know it's coming from a place of anxiety on my end, but I also thought the way you did, which is that it would probably be an interesting question to ponder for anyone into coffee.
People use cast iron frypans, in part, specifically to increase Fe in their diet. Corrosion might dull the cutting edges, but don't worry about health issues.
I also own an Aergrind. I believe Knock grinder steel burrs are specially treated to make them harder and rustproof. I wouldn't worry about it unless you continue to get your burrs wet.
Tried to find some info about this but wasn't able to confirm.
At any rate, thanks for your response.
Don't worry about it. People having been using RDT on their $3000 grinders for years and have not noticed any rust issues. A little bit of water isn't going to kill you. I spray my beans every time for my Monolith Flat and Compak K10.