Plugged grinder burrs!

Grinders are one of the keys to exceptional espresso. Discuss them here.
walt_in_hawaii

Postby walt_in_hawaii » Jun 13, 2018, 3:35 am

OK, this is the second time this has happened to me... the first was a couple weeks ago when I installed new burrs into an old Pavoni Zip... I took out the burrs, thinking must be a strange set or dull or something (they were new burrs). Now, I just installed a new set of SSP burrs into my Mazzer SJ; same thing happened! So I must be doing something wrong. I tighten them up while spinning the spindle by hand... and listen/watch for the burrs to touch; then back them off about half of one of the large graduations on the Mazzer's collar, the old set of burrs were calibrated about there for espresso singles.

Ran a handful of beans through... and it clogged up! Disassembled the burrs and found this:
Image

Looks pretty much exactly how the new burr set in the Pavoni looked. I think its a problem with seasoning, since this is only the second new set of burrs I have ever used, and same thing is happening. Problem is, I've never heard of anyone else running into this problem. I will clean them up, and I know from the Pavoni set, if I run it slightly coarser, it will be fine... but I can't use the coffee coming out of the grinder then, its just a tad too coarse for espresso and will run out in about 10 seconds or so. But when i get into superfine territory/about where I need to be for the Strega, they will clog up.... any insight into this?

aloha,
walt

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civ

Postby civ » Jun 13, 2018, 6:48 am

Hello:
walt_in_hawaii wrote:OK, this is the second time this has happened to me...

I don't think it is a burr problem.

Is it the same batch of beans in both cases?
Are they very fresh? Maybe inadvertently been exposed to humid conditions?

Try with some other beans and see what happens.

Cheers,

CIV

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Jake_G

Postby Jake_G » Jun 13, 2018, 7:54 am

Walt,

This happens to me about once every few months. I still don't have a grasp on why it happens, but I'm familiar enough with it to have a system to recover. My wife is not so fortunate, and it tends to happen when she's home alone :cry: .

I am proficient enough with it that I can recover the shot when it happens. When the burrs load up and your dose of beans is just swirling around in the throat, open the grind up while it's running until it finally starts grinding again. You can hear the tone change when the pre-breaker section of the burrs start grabbing beans. The first couple times you do this the dose will be waisted as the grinder spews a dose of drip grind beans in your face very quickly. But once you recognize the sound change, you can quickly set the ring right back where it was and finish the dose.

I have had Duranium burrs from Duramill in my SJ for 4 years now, and when this happens, I usually open the burrs ~30-40° to get the "she's gonna blow!" change in tone, then I swing it back maybe a hair coarser than it was and generally I end up with a fairly decent cup from the grinds. Oddly, the shots always pull slower when this happens, not faster...

Anyway, after this happens I can usually go about my grinding business uninterrupted for another 6 to 9 weeks and then it randomly does it again. For what it's worth, I don't remember this ever happening when I used the hopper. But I got tired of throwing away 5g every single morning... I'm very interested to hear if anyone has a cause and solution for this issue...

Good luck!

- Jake

walt_in_hawaii

Postby walt_in_hawaii » Jun 13, 2018, 12:42 pm

Thanks Jake!
I just took a bamboo skewer and cleaned each V manually, it just pops out if you rake it. Your solution sounds much easier, will keep it in mind... hmmm, I figured it was a seasoning issue because it has only happened to me with brand new burrs (from 2 different makers, 2 different machines).

The change in color of the plugged section's coffee means it saturated with oil? I don't think the burrs heat up that much so can't be cooking. If your burrs are still doing it 4 years later, this is worry some.

I did not do an alignment on the burrs when I installed them. I doubt that is the issue, but I think I should try, just to rule that out. Jake, did you do a shim/alignment of your 4 year old burrs? Has the frequency of clogging gone down over time, or is it about the same for you?

aloha,
walt

Aguirre

Postby Aguirre » Jun 13, 2018, 1:51 pm

civ wrote:Hello:

I don't think it is a burr problem.

Is it the same batch of beans in both cases?
Are they very fresh? Maybe inadvertently been exposed to humid conditions?

Try with some other beans and see what happens.

Cheers,

CIV


To me also seems this issue relates more to coffee than to grinder/burrs. Either humidity or oily (dark roast) beans

walt_in_hawaii

Postby walt_in_hawaii » replying to Aguirre » Jun 13, 2018, 3:19 pm

Hmmm, possibly. But the batch shown above was with a Guji that was roasted 2 days ago, roughly 48 hours post roast... taken very light, not quite out of 1C and no spotting whatsoever. I find the Guji darkens really quickly, so a 'normal' drop from the roaster looks invariably like you charcoaled it (ok I'm exaggerating, as usual) and kept it in too long... so nowdays I drop extra early on the Guji. For what its worth I don't think that was it... and the pic above is the very first grind on a brand new set of burrs out of the box with the Guji, not old or throwaway beans.

It comes to mind that there may have been some sort of protective sealant on the burrs put there by the factory, but that would not explain Jake's plugging since his burrs are years out and still doing it :(. But, just to rule that out I will remove my burrs and soak them in a nonpolar solvent to remove any protective film so we can make sure its not that.

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lancealot

Postby lancealot » Jun 13, 2018, 3:27 pm

What is that black / dark brown stuff on the finishing section of the burrs (the flat part right as the coffee exits)?
Is it oil? or Burned on bits? Does it rub off with a nail?
It don't look right. Could be a clue!

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Jake_G

Postby Jake_G » Jun 13, 2018, 4:40 pm

walt_in_hawaii wrote:Thanks Jake!
I just took a bamboo skewer and cleaned each V manually, it just pops out if you rake it. Your solution sounds much easier, will keep it in mind... hmmm, I figured it was a seasoning issue because it has only happened to me with brand new burrs (from 2 different makers, 2 different machines).

The change in color of the plugged section's coffee means it saturated with oil? I don't think the burrs heat up that much so can't be cooking. If your burrs are still doing it 4 years later, this is worry some.

I did not do an alignment on the burrs when I installed them. I doubt that is the issue, but I think I should try, just to rule that out. Jake, did you do a shim/alignment of your 4 year old burrs? Has the frequency of clogging gone down over time, or is it about the same for you?

aloha,
walt


Walt,

I aligned my burrs. They were very good from the factory, but there was a 45° segment between bolts on the fixed burr that was a bit high (further away from the rotating burr; ink remained). A little sliver of foil got me a bit better there but not perfect. The lower burr is exquisitely even. Like perfect even removal of ink. Makes me think I have a low spot on the upper burr that the entirety of the lower burr is scrubbing, but I didn't see evidence of a low sport on the upper fixed burr...

The burrs never clogged until I started single dosing in November. It has been an issue consistently since then. I think this is an issue of not enough back pressure and relatively conservative geometry on the pre-breaker section of the burrs. As I do a fact check of the MTBF, I stated earlier and the fact that I've only been single dosing for 7 months, I now think this is happening more frequently than I first thought. I'm thinking this is more like once every 3 weeks or so. But some of the events have been self-caused by just setting the grind too fine. Still, I think this is a monthly occurrence even when I am not fussing with the grind...

Also a great reason to machine a weighted plug that provides pressure all the way down the throat. My idea is a fixed bushing that necks the throat down to the inner diameter of the burr and then a weighted cylinder with a relief for the center bolt. Drop your dose and let the weight push the beans all the way into the pre-breaker section of the burrs.

Cheers!

- Jake

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espressme

Postby espressme » Jun 13, 2018, 5:55 pm

JMO, YMMV
Try grinding pre-cooked ( minute rice) rice for about a cup worth and then use a vacuum to clean up everything. It is an oil magnet.
The may be some residue but it does not change the flavor of a cup and is gone quickly.
JMO, works for me when the burrs clog on the vario and the Sette. On the Sette I use it once a month before doing the disassembly cleaning. I also like very light roasts.
richard penney LMWDP #090,

walt_in_hawaii

Postby walt_in_hawaii » Jun 13, 2018, 7:16 pm

lancealot wrote:What is that black / dark brown stuff on the finishing section of the burrs (the flat part right as the coffee exits)?
Is it oil? or Burned on bits? Does it rub off with a nail?
It don't look right. Could be a clue!


Lancealot, that's the problem. It's the coffee and I don't know why its undergoing a color change. I would have guessed that's the oils naturally present in coffee grounds, but it does not explain why its clumping up just there. I do not think temperature has anything to do with it, but if it ain't temp, very difficult to explain what other force would be present just there which could possibly explain what's happening. I wouldn't expect centripetal acceleration to be high enough to centrifuge oil out. Maybe my grinder is some kind of defacto dark energy generator? I should rename it the LHG (large hadron grinder)?