Coffee Bean Bridging

My coffee grinder sometimes pauses in its labors, and makes a high-pitched whining noise that is nigh unbearable to the uncaffeinated ear. The noise happens because even though there are plenty of beans in the hopper, they’ve managed to arrange themselves in such a way that they don’t fall down. A good jostle of the grinder will set things right.

This problem is not new. Random loose particles frequently produce such quasi-stable, gravity-defying arrangements. Back in the day when I was working on well drilling projects, we worried about it happening in the gravel that surrounds the well casing. This gravel is installed to prevent sand from the surrounding material from getting into the well and wrecking the pump. If the gravel “bridges” during installation, leaving a gravel-free gap underneath, that’s a place where sand will get in.


There are a number of ways to avoid gravel bridging. In fact, this is the subject of quite a few U.S. patents (I stopped counting after the first half-dozen or so). I was hoping that well drilling would give me some engineering inspiration that would make my mornings more pleasant, but no.

The cheapest way – the one included on technical specs for municipal water well contracts across Southern California – is to simply drop your gravel from as small a height above the top of the growing gravel pack as possible, and hope for the best. In the morning before coffee this can end up with a fully inverted bag of beans and a mess, if I’m not careful, but engineering is all about balancing competing priorities for your project.

More advanced ways include pouring the gravel in a high-viscosity slurry (perhaps I could embed the coffee beans in corn syrup? Mmmmm yum!) or using a complicated arrangement of screens, perforations, and funnels to drop the gravel. Much as I would love to infringe on ExxonMobil’s intellectual property every morning, I’m pretty sure these techniques are also nonstarters for coffee grinder adaptation.

Of course, the real reason people have invested so much energy into developing methods of pouring gravel is that you can’t just reach out and give the well a good thwack, like you can with a coffee grinder. If you could, I’m sure that is exactly what drillers would do.

Maybe the real lesson is that I need some OSHA-approved hearing protection to wear while I make breakfast.

Happy Monday, everyone.


  1. Ole wrote:

    The need for a thwack should encourage drilling in earthquake prone areas – if you get stuck, you can just wait for the next available quake to shake things up a bit? Be prepared to pay some serious overtime, though…

  2. Sean Carroll wrote:

    Man, science is everywhere. But understanding the physics of jamming is cold comfort when the coffee grinder starts whirring impotently.

    My solution: self-jostling coffee grinders. Was that one of the patents?

  3. chezjake wrote:

    Is it not at least hypothetically possible for a well driller to deliver that needed thwack from inside the well casing?

  4. Maria Brumm wrote:

    At least one of the patents was for a tool that you stick down the hole to dislodge the bridges.

    Thwacking from inside the casing would be difficult, just because you’ve got something on a really long drill string inside a relatively small-diameter hole – there’s no way to swing it around to build momentum. Also, you really don’t want to chance knocking off the end of your thwacker and losing it down the hole – even if you can ultimately fish it out, which is hardly a guarantee, it is a huge PITA.

  5. dad wrote:

    Gravel placement would seem immaterial to the coffee grinder whine problem. Placing the coffee beans is not the problem but it is in the agitation and changing of particle sizes when the beans are ground. As far as well casings—anyone ever invent a cam vibrator? I’m guessing casing thickness would affect results? If you patent this I’ll be happy with 5% (to buy my coffee beans). My Monday morning gift.

  6. Thermochronic wrote:

    Is this a blade or burr grinder? I constantly shake my blade grinder during use, but only because I am too poor to buy a proper burr grinder. Or better yet, a hand crank burr grinder, guaranteed not to overheat your beans during grinding. Perhaps by the next NSF facilities deadline I can request funds to study said phenomena.

  7. Kurt wrote:

    Off topic, but I was wondering if you, as the resident rock expert, can make anything of the rock that PZ recently blogged about.

  8. Lab Lemming wrote:

    If we packed the casing of your water well with coffee beans instead of gravel, then you wouldn’t need a coffee machine.

  9. Thermochronic wrote:

    I think if “going into industry” meant drilling for coffee beans, I would reconsider leaving academia.

  10. Silver Fox wrote:

    Then if you drilled a dry well, you could say, “it wasn’t worth a hill of beans.” ;)

  11. jkao wrote:

    Does the time it takes your coffee grinder to jam follow an exponential distribution? I saw a talk on this subject just two weeks ago:

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