Coffee Appreciation

Update: nothing to report.

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Don’t know how useful the penny is as a comparison as I’m pretty sure it’s an alloy with much lower copper content that copper piping etc.

What’s the going rate on a Silvia, about £250-300?
If I’m looking at a second hand machine with about £200 to spend, other than a Gaggia classic, is the Silvia still my best bet (and do people still rate the Silvia over the classic?).

Update pls.

This could be on BBC 2 with Brian Cox and Daira.

Don’t know how useful the penny is as a comparison as I’m pretty sure it’s an alloy with much lower copper content that copper piping etc.

I used a 1978 coin. Composition is 97% copper, 2.5% zinc, 0.5% tin up until September 1992. After that they've been copper-plated steel. Don't make me get a colleague to zap one in the SEM/FIB to check...

Update: still no change.

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My girlfriend, a certified chemist, says it won't dissolve. But it's like GCSE chemistry that she doesn't remember well.

Here's the "reactivity series" from Wikipedia

So I think Jonny nailed it by identifying that the sodium is more reactive than the copper and therefore nothing happens. Not sure how copper oxide fits in.

What about bases like Cafiza then? And also what's the point of running acid through a machine if it's too weak to dissolve anything? Only good for descaling I guess?

What about bases like Cafiza then? And also what's the point of running acid through a machine if it's too weak to dissolve anything? Only good for descaling I guess?

Yeah it's literally only for descaling. I've blocked my Classic in the past when the little flakes of scale blocked up the passage that feeds the group head from the boiler.

I think we decided that things like Puly Caff and Cafiza tabs were in fact sodium hydroxide pellets. Fat converts to soap when it's dissolved in sodium hydroxide. I'm guessing that's why it works so effectively with caked-on coffee residue. Long term though, it will also dissolve any aluminium parts on your machine. I was about to say the distribution puck in the group head, but I think it's actually made of zinc, not aluminium.

Look I came here to see the Queen’s face melt, are you gonna fucking sort it out or what?

Probably only sensible thing to do is for me do the same with copper pipe and a saturated citric acid solution.

Good knowledge.

Seems like you need nitric acid if you want to melt the queen's face. Whole reaction looks deadly...

https://youtu.be/FhvxaxFGO8M

That’s brilliant!

750g to be appreciated...

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Have you replaced the citric acid?
I'm going to suggest you do a quick pH test to check if it is indeed still an acidic solution?

It's organic acid chemistry. It's a bit more complicated, I think, than
acid + metal = salt + hydrogen

https://www.nature.com/news/2004/041115/full/041115-5.html

Lightly tarnished copper pipe in saturated citric acid solution.

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I suppose the argument is that the tarnish prevents the copper imparting a flavour on the water. I fail to see how you can descale without removing the tarnish though.

Citric acid won’t melt copper. It reacts with the Copper Oxide to give ionized Copper in solution with some other stuff. Depending on how tarnished if was, if you stick a steel nail in, the Copper Ions will stick to it and plate it.

I missed some posts and thought the penny had turned into a bar.

::runs off to find nail::

Dooope...Doesn't work with stainless I think.

Thats how copper pipes are born

Niche Zero