A question about coffee tar...

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A question about coffee tar...

Postby quoad » Tue Feb 24, 2009 10:41 am

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?
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RE: A question about coffee tar...

Postby bruceb » Tue Feb 24, 2009 12:00 pm

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. Image

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

Edit: Unlucky typo corrected
Three Francesconi (CMA) espresso machines - Rossi, San Marco, LaCimbali, Faema and 2 Mazzer Major grinders- CoffeeTech Maggionlino, Hottop, Alpenröst and HW Precision roasters.
I decided I needed a bit of a change so I roasted some Monsooned Malabar. That was a change!
Image
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Re: RE: A question about coffee tar...

Postby quoad » Tue Feb 24, 2009 1:16 pm

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. Image

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

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.
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RE: Re: RE: A question about coffee tar...

Postby bruceb » Tue Feb 24, 2009 1:38 pm

Hmmmmm, sounds like a thesis project brewing! Image
Three Francesconi (CMA) espresso machines - Rossi, San Marco, LaCimbali, Faema and 2 Mazzer Major grinders- CoffeeTech Maggionlino, Hottop, Alpenröst and HW Precision roasters.
I decided I needed a bit of a change so I roasted some Monsooned Malabar. That was a change!
Image
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Re: RE: Re: RE: A question about coffee tar...

Postby quoad » Tue Feb 24, 2009 7:33 pm

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


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 :)
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RE: Re: RE: Re: RE: A question about coffee tar...

Postby quoad » Fri Mar 20, 2009 1:28 pm

Image

Image

Image

Image

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

Image
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RE: Re: RE: Re: RE: A question about coffee tar...

Postby quoad » Wed Apr 01, 2009 11:30 am

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 :D

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

:oops:
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RE: Re: RE: Re: RE: A question about coffee tar...

Postby phil2spill » Sat Apr 04, 2009 4:45 pm

Your tap appears to have an aerator type thing there, quoad - that'll probably create some foaminess anyway I guess?
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RE: Re: RE: Re: RE: A question about coffee tar...

Postby kingseven » Sat Apr 04, 2009 6:18 pm

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...
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