Too Much Coffee

The drip coffee machine in our graduate parlour regularly gets left on.

Sometimes for a period of 2-4 days.

Quite possibly longer.

At the end of this kind of blitzkrieg, there's often a deep, baked, pure essence of coffee death left at the bottom of the jug.

Now...

What interests me is that when I wash the jug out, the coffee tar froths up. The amount of foam and the bubbliness have an... um... surface tension? Or a shape / form / appearance JUST like washing up liquid.

Any ideas why?

I can't imagine why, but it doesn't happen when we wash out the jug in our lab lounge. I will say, however, that the smell of the rehydrated sludge is probably one of the most unpleasant I know of. BTW, I don't drink anything that comes out of the machine in any case.

Are you sure the jug is rinsed well after using detergent on it? Maybe the coffee contains 10% Fairy.

Edit: Unlucky typo corrected

bruceb wrote:I can't imagine why, but it doesn't happen when we wash out the jug in our lab lounge. I will say, however, that the smell of the rehydrated sludge is probably one of the most unpleasant I know of. BTW, I don't drink anything that comes out of the machine in any case.

Are you sure the jug is rinsed well after using detergent on it? Maybe the coffee contains 10% Fairy.

Edit: Unlucky typo corrected

Absolutely positive there's no Fairy in there. This has happened multiple times, always with the same effect. And always starting with a burnt-out jug of beyond-sludge. We are talking two- to three-day baked dry gunk.

The machine is mostly used with godawful Sainsbury's sludge (sometimes with pre-espresso-ground coffee...), but I'll sometimes bring in some fresh ground if I'm going to be working here. It's either that or the Gaggia... And the graduate parlour Gaggia... genuinely doesn't bear mention.

Hmmmmm, sounds like a thesis project brewing!

bruceb wrote:Hmmmmm, sounds like a thesis project brewing!

WELL.

I'm a criminologist.

IMO this definitely counts as a crime against coffee.

Next time I come across a baked-dry tarball, I'll try and get some pics / video of the foaming

AND after the foam had been left to settle for a minute or so...

OK, so I'm making an absolute tonne of filter coffee for work at the moment.

And it's clear that this happens to all leftover coffee, regardless of how baked-in its been.

I'd just never seen it at home, because there's never any leftover coffee

I guess the principle's exactly the same as for crema, duh.

Your tap appears to have an aerator type thing there, quoad - that'll probably create some foaminess anyway I guess?

Likely the same reason you get crema. Some of the roast by products - usually melanoidins - are good surfactants. They are pretty bomb proof as compounds (they did survive the roasting process after all).

Get some Cafiza in there and give it a damn good soak. Then a scrub. Rinse and repeat etc...