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My espresso machine has a pretty impressive drip tray, at just around 1.5 liters in capacity, it holds quite a bit.

The problem is, if I empty it only when full, the bottom part of it has this really slippery, rather slimy surface which is extremely difficult to scrub. To be clear, it comes off easy enough, but tends to collect in nooks and corners.

I've tried adding a cap full of vinegar to the tray after cleaning and replacing it, this didn't make a noticeable difference. Even if I empty the tray when it's half full, there's still a bit of build up.

Is there anything else I can put in the bottom of the tray that wouldn't come with any competing odors to the coffee I'm brewing, but help keep this (as far as I can tell) 'water gunk' from forming? I'd really like to avoid dumping and cleaning the tray daily, as it is a bit of a chore.

  • Do you know what the "water gunk" is? E.g., scale, mould/bacteria/algae, the last drips of coffee, ...? Perhaps it's the same as builds up in, e.g., water-filter pitchers. What's the source of the water drips, and is it just water (otherwise clear)? I assume this is commercial-application; I can't otherwise imagine >1L of drips... Fascinating! Sorry for all the questions. – hoc_age Feb 12 '15 at 15:20
  • From what I can tell, it's mostly what gets dumped out of the boiler. It's a single boiler system, but it will drop the holding (heated) tank when I switch between extraction and using the wand. It also dumps if it has remaining hot water in it after a period of no use. Grounds are the only other thing commonly going in there, but those mostly get caught by a special catcher that's part of the drip pan system. – Tim Post Feb 12 '15 at 15:46
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If what you're seeing is mold or algae you may want to add a few table spoons of salt to the drip pan.

I'm guessing that your slime is probably a fungus of some kind, rather than an algae. It has found a rather nice living arrangement for a fungi. Plenty of warm water and decomposing coffee, with very little light.

Salt should in most cases prevent fungal growth, this may sound odd but it will dehydrate the cells even when they're immersed in water, sort of a "water, water everywhere but not a drop to drink".

If you would rather get high tech with it, you could try a UV light, similar to the ones used in AC systems. The harsh UV rays will kill most molds and prevent them from colonizing.

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You really just need to empty the drip tray more often. The slime is algae or bacteria living and breeding in the nutrient-rich and warm tray water.

It sounds like you're interpreting the large drip tray as rationale to only clean it when it gets full — it’s not. Your tray is huge, and it’s probably intended for more industrial applications (like a coffee shop) that could produce a liter of waste water a day (too little time for slime to form.

If you need motivation to clean the tray more frequently, think about all the nastiness that's only a few inches from the coffee you’re making. Think of all the nasty mold and slime spores floating around in the air and landing in your newly brewed beverage.

I bet you rinse it out every couple of days now and wash it once a week.

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