How to clean hardened oil gunk from a burr coffee grinder?

April 16, 2023 10:33 AM

We made the unfortunate mistake of using our primary burr grinder (Cuisinart DBM-8) for flavored coffee beans the past few weeks. Now the plastic basins have hardened gunk and I think I just made it worse. Help!

When I went to remove and clean the grinder's plastic basin components today, it had a lot of hardened gunk from the flavored coffee oils (surprise).

After soapy water and gentle scraping/brushing did not work, I soaked the plastic components in very very hot (not boiling) soapy water for about an hour.

I came back to this (photos). Before, these plastic basins were clear. Now they're cloudy and the oils are still hard and still won't come off.

I couldn't find much on Reddit about this specific scenario - there's plenty about cleaning the oils from the grinder itself, but little about removing hardened oils from the plastic. I did see people recommend Grindz tablets (not sure they apply to this scenario either). I also read a recommendation to use isopropyl alcohol and a stiff toothbrush, but I tried that and had very little success.

What can I do to fix this? I really would like to remove these oils and have a clean, clear burr grinder again.


And yes, next time we have flavored coffee, we'll stick to using our less-fancy blade grinder - and clean it out daily. I feel already feel like a bozo so no need to tell me so - I'm well aware! :-)

posted by nightrecordings to Home & Garden (11 answers total)

Have you tried bleach, maybe diluted + on a cotton ball to limit the contact area? Otherwise, I really don’t know of great ways to clean discolored plastic.
posted by Maecenas at 11:04 AM on April 16, 2023

Does the brown residue come off if you scrape it with a fingernail? It might just need a bit more than "gentle" scraping, but still with something not harder than the plastic (I've encountered this inside a grinder before, less so on the plastic). The cloudiness I'm not sure of, I've had multiple burr grinders (including this exact model) and not seen that effect, but it is not super obvious to me that it is something that would result from coffee oils. Rather, it looks like something like soap film, hard water deposits, or the result of many small scratches if you used an abrasive that was too hard. (If you search for cleaning cloudy plastic you get many suggestions to deal with the various possibilities, though for the latter your only option is really polishing it.) You can also buy a replacement grind chamber, though it's a bit expensive proportional to what a cuisinart burr grinder costs in the first place; I guess upgrading a bit could also be a more extreme option...

I did see people recommend Grindz tablets

Grindz tables won't fix the problems in the linked images, but if you have that much brown gunk accrued in the grind chamber I guarantee it's also inside the grinder and on the burrs, so it would definitely be worth running cycles of grindz or similar tablets (and/or doing something else to clean the burrs, e.g. using a stiff brush). To be honest I didn't find this model the most cleanable of the burr grinders I've had.
posted by advil at 11:14 AM on April 16, 2023

Response by poster: For context, in response to the first commenter: as far as I can tell, it doesn't appear that the actual plastic is discolored, but rather there is a thin but difficult to penetrate layer of hard oil. A tiny bit scraped away at one point and I could see the clear plastic again. What I think I need is a solution to remove the gunk more efficiently (and would prefer to avoid bleach).

Since isopropyl alcohol hasn't really worked, does anyone know if vinegar would do any good? Or (separately) baking soda?
posted by nightrecordings at 11:17 AM on April 16, 2023

Denture cleaning tablets work well to clean the plastic parts of my burr grinder (and they're handy to have around for cleaning pots).
posted by dws at 11:22 AM on April 16, 2023

I would run Grindz through the burrs until there's no residue that comes out and then purge with some non oily beans. If you can, disassemble the burrs and brush out.

For the plastic pieces that have oils all over them, soak in cafiza solution. (Do not do this for the burrs as they will likely rust.) I've used cafiza for this in the past and it's magical.
posted by kdar at 11:24 AM on April 16, 2023 [2 favorites]

Yes, soak the plastic bits for 10 minutes or so in PuroCaf or an equivalent, that's what it's for! You can also clean the metal with a purocaf solution but you should absolutely dry it completely before putting it back together, and don't soak your burrs longer than a minute or two (really just scrubbing them with the solution, rinsing well and then drying them should be enough)
Go ahead and run a few batches of clean disposable beans through once it's done if you're nervous about any lingering chemicals and if you're not sure whether the flavour aroma is totally out.
posted by Grim Fridge at 11:29 AM on April 16, 2023 [1 favorite]

Was there any clove oil involved?
posted by stray at 1:43 PM on April 16, 2023 [1 favorite]

I would try mineral oil. It seems to dissolve pretty much any oil residue, but is non-toxic and odor-free. I've never seen it attack any plastic (I use it to clean my laptop, including the screen), but I'd test it on a small area first. Dab it on with a cotton swab, let it sit for 10-15 minutes, and then rub with another swab or a piece of paper towel. Repeat as needed.

Mineral oil should available in any pharmacy (in the US). It's baby oil without the fragrance. If you can't find it in a pharmacy, you can pay through the nose for it at a hardware store as "cutting board oil."
posted by bricoleur at 4:56 PM on April 16, 2023

If it's oil, you could see if it will soften with another oil. I often use mayonnaise for things like this - smear on a layer and let it sit for a bit.
posted by lulu68 at 8:25 PM on April 16, 2023

have a clean, clear burr grinder again

If this is the goal, I would stop doing things that are likely to damage the plastic on this relatively cheap grinder, set it aside for flavored coffee only, and upgrade your real beans to a nice Baratza.

Cafiza is great for coffee oils, but I just wouldn’t trust it to get this machine back to newish, given that flavored beans aren’t just made of coffee. Also it works best on metal (carafes, portafilters, grouphead screens)
posted by supercres at 10:40 PM on April 16, 2023 [1 favorite]

There are cleaning 'salts' you dissolve in hot water, for cleaning commercial coffee machines at the end of each day.
These should break down the coffee oils in your grinder with a soak (protecting any electrics), in the same way they do with the main machines.
posted by many-things at 12:22 AM on April 17, 2023