Citric acid to water solution for descale

#1: Post by **walshman** » March 24th, 2023, 8:29 am

Hi all. I'm going to descale my faema legend (5 or 6 litre boiler) and forgotten what the quantity of citrus acid to water would be. I've done it years ago but completely forgot what my measurements were. Any help please. Thanks.
Dennis

#2: Post by **Sw1ssdude** » March 24th, 2023, 10:13 am

The more the better... In six liters you can easily dissolve one kilogram of citric acid. However, it really depends how crusty your boiler is. Maybe 500g will be plenty to get light scale buildup off your boiler..

#3: Post by **Nunas** » March 24th, 2023, 11:25 am

50 to 100 ml of liquid citric acid, or 30 to 60 grams of powdered citric acid per litre, is what's usually recommended.

#4: Post by **BaristaBoy E61** » March 24th, 2023, 1:22 pm

I use 2-oz to a full 2.3-litre reservoir. So that's about 1-oz per litre.

#5: Post by **LittleCoffee** » March 24th, 2023, 3:10 pm

Jim Schulmans water faq says 8-12g citric acid per 1l.

#6: Post by **homeburrero** » March 24th, 2023, 4:00 pm

Sw1ssdude wrote:The more the better... In six liters you can easily dissolve one kilogram of citric acid.

Disagree. I think Nunas, BaristaBoy, and LittleCoffee all have it right.

Using more citric would dissolve more limescale, but at the expense of being a much harsher acid (lower pH) that would have a corrosive effect. Be aware that the insides of the machine has exposed metals, and even where it's coated with limescale, and that limescale is porous.

To get the same limescale dissolving capacity as, say, full strength white vinegar (5% acetic acid), you would need 56 g/L of anhydrous citric acid. That's just under 4 tablespoons per liter. Still, that would give you a relatively harsh acid with an initial pH of about 1.6. (Acetic is a weaker acid, and the initial pH of 5% acetic would be only around 2.4.)

Using the lower Jim Schulman amount, about 10 g/L, about 2 teaspoons per liter, is sensible from a standpoint of protecting your machine from harsh acids. It would not dissolve as much limescale but you can make up for that by repeating the descale only if necessary with a fresh solution. The initial pH of 10 g/L anhydrous citric acid would be about 2.2 -- comparable to full strength white vinegar.

#7: Post by **Sw1ssdude** » March 26th, 2023, 5:54 pm

Yes, you're right.

I only use citric acid to descale completely dismantled machines, and usually do rinses between acid soaking phases, to check on the progress.

For 'assembled descaling' i use Durgol, and follow the instructions on the bottle.

But i stand by my method (for my very simple machines): more citric acid gets the job done quicker.