MCALheaven wrote:Yes, plain vinegar, 5% acid. Continuous heat for an hour is the secret. Water/vinegar mixture that is allowed to cool (as in turning off the machine) will take many, many hours and not do as good a job. In fact, only because of continuous heat will 25/75 vinegar water work. Without the heat, it's no good. Very safe levels of acid this way, IMO. 50/50 vinegar water is only needed when not enough continuous heat is applied in my experience. Not an expert, but I have plenty of practice descaling water distillers and I can guarantee you this works as well or better than any descaling product I've tried. Good luck to you.

Do you think this would be appropriate? It's the only thing I can really spot in the supermarkets nearby: https://www.sainsburys.co.uk/shop/gb/gr ... egar-568ml

It's described as both distilled white vinegar, and malt vinegar. 5%.

homeburrero wrote:I believe plain white vinegar is typically 5-6% acetic acid (appx 0.8 molar). Dr. Pavlis said he diluted white vinegar to 50:50. On tough jobs he might descale repeatedly, with less than 1 hour soaks. For helping to dissolve scale in the pressurestat pipe he would cycle the machine up to pressure a few times - see this post: La Pavoni Europiccola not heating

That makes me think it's not carbonate scale, which should have dissolved in that Oust (citric acid*) descaler. I wonder if maybe you're dealing with calcium sulfate scale, or even worse, silica. One way of dealing with that is to start using very clean, soft water that has no sulfate or silica, and let that white stuff slowly dissolve as you use the machine. Here's some discussion about that: The chemistry of scale in espresso machine boilers [FAQ].

*Edit addition: The liquid 'all-purpose' Oust descaler is, according to the MSDS, lactic acid rather than citric acid.

Thank you for that. I am / was also concerned it might not be regular scale... we have quite hard water, we get scale around the taps/shower, in the regular kettle, but it also seems to come off quite easily with cleaning products.

Most of the scale has came out of the La Pavoni, would it be weird for it to have two types of scale? It is really just right on the base, and on the coil that it's stuck. But even then, it is fragmenting. The scale on the coil has cracks and flecks on it now, it is budging, just so slowly. So it is probably the Oust...

On the bottle it says "contains critic acid", but if you say it's mostly lactic acid based, that might explain things... I wonder if you could just use lemon juice...

After multiple rinses and a mostly clean machine, my coffee this morning was beautiful.

But I still want to kill off all this scale before I return to regular use... hopefully the vinegar will sort it out...

RHP wrote:Most of the scale has came out of the La Pavoni, would it be weird for it to have two types of scale? It is really just right on the base, and on the coil that it's stuck. But even then, it is fragmenting. The scale on the coil has cracks and flecks on it now, it is budging, just so slowly.

Scale can be a mixture of different carbonates and sulfates. To have a different layer at the bottom does seem odd, but might be explained if the machine had a history of different water in the past.

If it's fragmenting and settling you may want to make sure it isn't settling in the pressurestat pipe. You can remove the pressurestat and give the pipe a rinsing/cleaning with wire or pipe cleaner. Don't remove the pipe from the boiler - just use two wrenches to remove the pressurestat from the pipe fitting if you do that.

RHP wrote:On the bottle it says "contains critic acid", but if you say it's mostly lactic acid based, that might explain things... I wonder if you could just use lemon juice...

You probably could, but citric acid is easier to get the strength just right. I think most Oust descaler products are citric acid, but I did run across that one that appears to be lactic acid. Shouldn't make much difference. Lactic is weaker than citric at the same molarity, (and acetic is weaker than either) but that doesn't matter too much because you can get any of them to about the same acidity by using higher or lower concentrations.

RHP wrote:Do you think this would be appropriate? It's the only thing I can really spot in the supermarkets nearby: https://www.sainsburys.co.uk/shop/gb/gr ... egar-568ml

It's described as both distilled white vinegar, and malt vinegar. 5%.

The acidity is the same percent as what we call plain vinegar here in the States so I would guess yes, but can't say for sure.

homeburrero wrote:Scale can be a mixture of different carbonates and sulfates. To have a different layer at the bottom does seem odd, but might be explained if the machine had a history of different water in the past.

If it's fragmenting and settling you may want to make sure it isn't settling in the pressurestat pipe. You can remove the pressurestat and give the pipe a rinsing/cleaning with wire or pipe cleaner. Don't remove the pipe from the boiler - just use two wrenches to remove the pressurestat from the pipe fitting if you do that.

You probably could, but citric acid is easier to get the strength just right. I think most Oust descaler products are citric acid, but I did run across that one that appears to be lactic acid. Shouldn't make much difference. Lactic is weaker than citric at the same molarity, (and acetic is weaker than either) but that doesn't matter too much because you can get any of them to about the same acidity by using higher or lower concentrations.

I work with a guy who has a Ph.D in Inorganic Chemistry. He suggested white vinegar when I described the types of scale we see in espresso machines. It also cited the fact that there is no need to heat the vinegar solution to increase its effectiveness as an added bonus. All of this is to back-up exactly what homeburrero has suggested in this thread. He has never been to this web site and didn't know our late friend Dr Pavlis. It was the ultimate second opinion scenario.

Lastly, as far as the smell of vinegar goes, I look at that issue as a bonus. I know when I've thoroughly removed all of the solution.

You guys are so knowledgable, thank you for sharing! Just a quick photo of what the scale looks like after I'd done the cleaning cycles, and have since pulled a few shots. It doesn't seem so bad... I am hopeful a go with some vinegar will sort it out...

Heating vinegar may not improve effectiveness but it does make it work much, much faster. I consider that a useful advantage. Having done this several hundred times (with water distillers) I have to say that the heat applied to vinegar does make a huge difference for me, even if it's only because I'm too impatient to wait 12-24 hours.