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Every morning when I get up, I use this coffee grinder to grind beans for my morning coffee. grinder

When I remove and subsequently open the top of the bin, I often find that enough static electricity has built up in the grounds/bin that particles of coffee will literally fly out of the bin and onto my hand and the counter, making a mess. Coffee will also be stuck to the sides of the bin to varying degrees, making it necessary to rap the bin on the counter in order to dislodge the particles from the sides. Of course, more then fly out and increase the mess on my counter.

I have made some observations of a few factors that seem to affect this:

  1. It happens to some degree with most beans, but I've noticed that the darker the roast, the greater the static charge. It's the worst with French Roast (my favorite), which is also oily since they add oil to the beans in the roasting process.
  2. The coarseness of the grind doesn't seem to matter except that a coarse grind produces heavier particles which don't tend to fly as far.
  3. Cleaning the bin had no observable effect on the static.
  4. Waiting a while after grinding doesn't seem to do much to alleviate the problem. I've ground the beans and waited 10-20 minutes before removing the bin and observed no apparent decrease in the amount of static.
  5. It is worse in winter when the air is dry, but I don't really let my house get too humid.
  6. Google reveals that this problem is not specific to any one brand or model of grinder, but seems to plague most burr grinders.

My questions are these:

  1. What is the cause of this static charge in the grinding process?
  2. What modifications can the end-user make to either the grinder or the process to prevent static buildup?
  3. How could this be eliminated in the design itself?
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    $\begingroup$ A related question on Seasoned Advice addresses this from the end-user's perspective: How do you reduce static in a coffee grinder? $\endgroup$
    – Air
    Sep 4, 2015 at 15:38
  • $\begingroup$ Just throw in a dryer sheet :) $\endgroup$
    – Chris Mueller
    Sep 4, 2015 at 15:51
  • $\begingroup$ Have tried placing the metal top as a stove. This might help. Just a thought. Also there is a coffee stackexchange I am sure someone over there has simple solution. $\endgroup$
    – Mahendra Gunawardena
    Sep 4, 2015 at 19:08

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What is the cause of this static charge in the grinding process?

My thought is that the coffee grinder is essentially acting like a Van de Graaff generator. Since the coffee maker likely has a plastic frame, rests (most likely) on rubber feet, and the electrical wiring (most likely) is insulated from the grinding mechanism, you have the potential for charge to be stored in the grinder. If I had to guess, there's probably some insulative gap in the grinder drive train between it and the motor that does not allow grounding of the charge. This may be by design to avoid the potential for electric shock.

Also, assuming you're using it on a countertop that is not metallic (i.e., nonconductive), even of there was a discharge path from the grinder through the body, it can't ground out anyway since the counter won't conduct the charge.

What modifications can the end-user make to either the grinder or the process to prevent static buildup?

I might try soldering a grounding wire to the outside of the burr cone. This would have to be connected to a ground somehow. For example, you could open up an electrical outlet (turn the power off to the outlet first!) and attach the grounding wire to the metal outlet box. The outlet box should be connected to your house's main ground. This will allow the charge to dissipate.

If this had a grounded plug (three-prong), I might just connect the grounding wire to the ground in the plug wire. However, this is not the case for this particular coffee grinder.

Also, dryness tends to be conducive to static buildup. For example, it's much easier to shock yourself on a doorknob in the middle of winter (very dry air) than in the summer (usually humid air, unless you live in a desert or something). Wetting the beans a bit may help too.

How could this be eliminated in the design itself?

If the grinder had more metallic parts, especially in the main frame and the hoppers, and these parts were all connected in such a way as to allow discharge to the ground, it would likely eliminate the static problem altogether.

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  • $\begingroup$ Might be easier / safer to convert the machine to use a grounded plug instead of running a separate wire for the ground. If you're going to go to the effort of opening up the case and attaching an internal ground wire, switching to a grounded 3-prong code is trivial to do at the same time. $\endgroup$
    – user16
    Sep 4, 2015 at 18:24
  • $\begingroup$ This is true. I agree my version is a little more hack-y, but it does give a quick-and-dirty way to get the job done. I don't know that it would be safer since you'd have to make sure you rewire the plug correctly. Soldering a copper wire onto a bare piece of metal is easier than making sure you have the wiring leads correct for a plug (not that it will probably matter being AC). $\endgroup$
    – grfrazee
    Sep 4, 2015 at 18:49
  • $\begingroup$ Generally speaking, the wires within an appliance cord are still color coded. From a manufacturing point of view, that's a very good thing as you can simply instruct the assembly line workers "Attach the black wire here and here. Attach the white one there and there." Ground wires tend to have a green sheathing. $\endgroup$
    – user16
    Sep 4, 2015 at 18:54
  • $\begingroup$ A valid point. However, based on the OP's minimal understanding of the mechanism behind static electricity, I'm hazarding a guess that they may not be particularly knowledgeable on electrical wiring. Hence, I'm trying to make as "dummy-proof" an answer as possible. $\endgroup$
    – grfrazee
    Sep 4, 2015 at 19:03
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    $\begingroup$ @gfrazee I think you're spot-on with your idea that the grinder is essentially a VanDeGraaf generator. Re-wiring it with a 3 prong plug connecting the ground wire to the burr wouldn't be hard, your guess about my knowledge of electrical wiring is off. I'm no expert, but I'm no "dummy" either. The KitchenAid grinder has a metal frame and a 3 prong plug and mentions "no staticky mess" in the marketing materials. It also costs $300, which is significant. $\endgroup$
    – DLS3141
    Sep 5, 2015 at 14:49
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Without getting into the why of static and grinding, I think the problem always lies with these plastic bins that the grinds end up in. Glass would be much better.

The simple solution which nobody has mentioned here, is to quickly dip a spoon in water and briefly stir the beans adding a few drops right before grinding. Problem solved.

The more interesting question is why does this easy hack work so well?

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