The Auroras I have are HX machines. They both have a brew reservoir which sits behind the group and is fed by the HX. The reservoir is a cast brass fitting that is brazed onto the boiler. The brew water sits inside this reservoir for as long as the machine is idle.

Ok, so if it is an HX don't you usually flush before a shot? Has anyone tested the water coming out of groups like this to see how much actually leaches into the water particularly after many, many years of use?

JohnB. wrote:Ok, so if it is an HX don't you usually flush before a shot?

No actually. That's the beauty of the Aurora, or when a HX is well designed. You can do without flush and pull a shot just right. I had it measured a while ago. But after reading Thomas' comment I now think there is no harm flushing!

About leeching, i personally see no major concern. Toxicity is in the dosage. We're only taking less than 60mL of water at a time. If anything, any of the surface contaminant would've leeched out long ago with decades of usage. Plus, if there is a bit of lime scale so that would make leeching even more unlikely. Unfortunately I would love to, but don't have access to measure it.

samuellaw178 wrote:No actually. That's the beauty of the Aurora, or when a HX is well designed. You can do without flush and pull a shot just right. I had it measured a while ago. But after reading Thomas' comment I now think there is no harm flushing!

There's no one temperature that's right for every coffee.

Well, it's in a good enough range for me 95% of the time (for light to medium roast range). An untuned HX will run hot and burn the heck out of the coffee, and that's what I am comparing to and what I thought you had in mind about flushing.

If I want a lower temp, I can lower the boiler pressure (I am currently running at 1.2-1.3 bar so plenty of room to go down). If a higher temperature needed, do a quick flush before.

Here's the post where I measured mine. The machine was idle for a couple hours and pulled a shot with no flush. Peak temp was about 92.6C for the first shot. Second shot peak temp was about 93.5C, with some flushing between the two shots to wash the portafilter. Otherwise the temp would be even closer. if I do some flush before the first shot, to refresh the water in the reservoir, the 1st and 2nd shot temp would also be closer together. Good enough I reckon for a design from the 70s!


Sorry Thomas for the sidetrack. I am really keen to see the modern incarnation of your Aurora!

JohnB. wrote:Ok, so if it is an HX don't you usually flush before a shot? Has anyone tested the water coming out of groups like this to see how much actually leaches into the water particularly after many, many years of use?

I am not following you. Could you explain me why there would be a leach problem in a HX? Would it be the same in a dipper?

I'm not the one claiming that there is a leaching problem or that it's something anyone needs to worry about. Read the prior posts.

On the subject of leaching.
While I have not tested the water from any vintage machines, what I can say is the following:

1 - Dezincification, i.e. the corrosion of brass by water borne acids (like coffee) and salts, is, as the name suggests, the removal of zinc from the crystal matrix of the composite metal. The process leaves behind a soft honeycomb of copper and exposes the other elements present in the alloy which may leach into the water they are in contact with. I have seen evidence of slight corrosion on both of the vintage groups that I own. It is hard to tell how deeply the corrosion extends into the brass.

2 - Lead is particularly bad because it crystallizes at the surface of castings as the molten metal freezes resulting in a high concentration of the metal close to the wetted surface.

3 - While the lead content of the alloy used in the vintage Brugnetti castings is fairly low, it is still four times what the law in California (for example) allows. If the group is made with around 3.5Kg of brass, it contains 35g of lead, some portion of which will be on the wetted surface.

4 - Lead and the other undesirable additives to brass alloys have been outlawed for use in potable water applications with good reason: they aren't good for you.

All that being said, as an espresso is a small quantity of fluid, and it seems unlikely that the levels of metals would be anywhere near being mortally dangerous. In all likelihood, I get exposed to more lead handling my house keys. However, in my view, no lead is better than some lead and I want to use an alloy that meets or exceeds the "lead-free" laws.

SHEEEEEEET METAL!



Should be here in a week or so!

bidoowee wrote:I finished up the package of cad drawings during a trip to Italy where I had some great (and some not so great) coffee. The best was, of all places, in terminal 3 at Rome Airport at a generic chain café. That is one of the things I love about Italy - the last time I was there the best coffee I had was in a gas station by the side of the highway - great coffee is normal.
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I was in Naples for a few days in May. The best espresso I had was at a counter-bar at the airport, and I tried some of the most renowned coffee bars in town. But it was all good, and it was all pulled in lever machines.

I enjoy this thread, even though my mechanical experience culminates in changing piston seals.

Matt