Nunas wrote:Citric acid is great stuff. We once bought a house in which the dishwasher and clothes washer were literally caked with scale. It was so bad that we were considering ripping them out and buying new. Knowing how well vinegar works on coffee machines, we ran some through both. A lot of the scale went away, but most stayed. We bought pure citric acid (Lemishine), and one run of that made the machines shiny as new.

I had the opposite experience trying to remove nasty mineral deposits from my old Vivaldi's boilers. Tried various strengths of citric acid solutions over several days but it hardly touched it. Filled the boilers with room temp white vinegar & left it in overnight. Next day all the deposits were gone.

Yes @WWWired, that's the one

@Nunas, I think you are on to something. I had a benchtop water filter that used to produce blackish sediment whenever I installed a new filter. Some of that may have gotten into the machine. I have a new under sink product now and the water is absolutely clear.

Do you have a suggestion on the concentration of citric acid I should run through my machine?

Thanks again for your thoughtful and insightful suggestions, they have really helped.

I'd go with something not too strong, given all the descaling you've already done. Check this out https://www.homegrounds.co/how-to-desca ... o-machine/

Thanks @Nunas. I'll post back on the outcomes

C8H10N4O24teepee wrote:Do you have a suggestion on the concentration of citric acid I should run through my machine?

That post Nunas linked said "A popular citric acid descaler recipe has a citric acid descaling ratio of one quart of water to two tablespoons of citric acid." I think that's a little strong. A common recommendation is 1 tablespoon per liter (Orphan Espresso often recommended this.) In a previous thread I did a little back of napkin calculating and came up with some advice about that, including this comparison with full strength white vinegar:

How to do citric acid bath?:

homeburrero, in post linked above wrote: Full strength white vinegar (5%, about 0.8 Molar acetic acid) is quite a bit less acidic than citric at 1 tablespoon per liter, even though the latter is only about a 0.1 Molar solution. Difference in initial pH would be about 2.4 for the vinegar and about 2.1 for the citric. That may not look like much, but because pH is a log scale it means the citric has over twice the concentration of [H⁺] ions. The citric would work faster and be more corrosive, but would dissolve less scale before it was neutralized (you may need to change to fresh descaling solution more often.)

Well, I used 3 tablespoons per litre which I let sit in the tank and internals for 25 minutes. I then rinsed 3 times with the probe disconnected so as to over fill and then 10 more times with the probe connected. In the end I had to do a second run through for the HX / grouphead circuit as the rinse still contained sediment and was very milky. I did not subject the boiler to a second bath. After the second run through the HX / grouphead I flushed again another 10 times. This time I got clear water.

I assume the number of flushes I ran have neutralised the citric acid and that I don't have to run a neutraliser like baking soda through?

Thanks for all the help, especially to @Nunas

Correct, with so many flushes, you'd statistically removed all the acid, even though a bit of water is left behind each time. It sounds like you're finally in the clear here! Now, feed your machine high quality water and flush your filters before using, and you should be fine.

Thanks again for all your help @Nunas. I'm a more edified barista thanks to you.