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I'm restoring an old coffee grinder and I want to give the grinder mechanism a nice zinc / silver coating.

But I read it is not safe for zinc to be in contact with acidic foods.

When I look at the pH, coffee's is 4.6 – 4.3 which is quite acidic: https://angelscup.com/blog/taste/coffee-acidity-flavor-ph-acid-reflux-and-low-acid-coffee/

Not sure if the zinc and coffee are likely to react in such a scenario. Should I maybe choose a silver plating?

Before cleaning with citric acid.

After cleaning with citric acid, Al foil and baking soda

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    $\begingroup$ [I don't use a coffee grinder] Assuming your beans are fairly dry, then the acidic nature of coffee isn't really a problem. In fact, electroplating metal articles with zinc is otherwise a common method of protecting the metal from corrosion: Galvanization [ en.wikipedia.org/wiki/Galvanization ] $\endgroup$ – paracetamol Jul 10 '17 at 14:36
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    $\begingroup$ and would you go for silver or zinc coating? which is more safer? $\endgroup$ – Peter Lapisu Jul 10 '17 at 14:37
  • $\begingroup$ Meh, since all you're doing is coating/plating the grinder components, it wouldn't be particularly pricey to use silver (since you won't need much silver anyways), plus, it does a better job at protecting metal from corrosion (assuming you did plate it properly). Zinc should work too, but go for it only if you're pretty sure that you'll store the grinder (component) in a nice, dry place ...and grind thoroughly dried beans with it. Also, nice job cleaning the grinder ;) $\endgroup$ – paracetamol Jul 10 '17 at 14:43
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    $\begingroup$ My two cents: You should use zinc as a sacrificial coating, so that even if the zinc coat wears off, the iron beneath won't rust. However, use silver if you want an inert coating, that will keep it safe as long as the coating is intact. If a silver coating is broken, corrosion begins immediately. $\endgroup$ – Pritt says Reinstate Monica Jul 10 '17 at 15:16
  • $\begingroup$ Maybe i can do zinc and than silver $\endgroup$ – Peter Lapisu Jul 10 '17 at 17:55
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Because the burr ( grinding head ) is steel and maybe the bowl it fits into , why not leave the shaft as bare steel ? As long as the beans are dry there will be very little corrosion; maybe wipe the shaft with a paper towel once a week to prevent any coffee powder from building up on it. And you could wipe a little vegetable oil on the shaft occasionally.

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  • $\begingroup$ I use a $ 20 spice grinder for coffee. $\endgroup$ – blacksmith37 Feb 12 at 21:44
  • $\begingroup$ I upvoted this because it make perfect sense. Why plate for no functional reason, and wonder about corrosion, metal particles, etc., when steel is simply perfect for this. $\endgroup$ – Ed V Feb 13 at 1:10
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If you plate the pieces with zinc or silver, the main source of zinc/silver in the ground coffee will be from abrasion between the parts and the coffee beans and not from chemical attack.

A few milligrams of zinc or silver (or iron for that matter) won't to do any harm to your health, specially if diluted in many coffee cups along several months or years.

In fact, Zinc was used therapeutically in dosages upwards of hundreds of milligrams per day for months, or more, with no permanent health issues.

Silver, on the other hand, has much lower acceptable exposure limits and while not particularly toxic, I'd not put it in parts of the device that are guaranteed to put metallic silver into the ground beans.

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