La Pavoni Europiccola - the effect adding baking soda to water has on the shot

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#1: Post by bobsy »

On another thread I mentioned the copper leaching issue I had with my boiler caused by my RO water being too acidic (pH 6).
I have solved that issue by bringing the pH of my water closer to the 7 range. I've done so by adding 3 grams of baking soda to 800mL of RO water. Now the water in my boiler remains crystal clear.

This has unfortunately caused some side effects.

1. Pulling on the lever is much harder than before. I had to grind coarser by 3 levels with the Niche, and even so, I notice it gets progressively harder the further I am bringing that lever down. As if that baking soda is clogging the shower screen somehow. The shot looks borderline syropy.

2. Once I've pulled the lever all the way down, it goes back up again slightly (it didn't use to do that, and I always get rid of false pressure and pump the lever 10 times before pulling the shot).

3. When inspecting the coffee in the puck after the pull, it looks dark and burned to a crisp, although I use medium roasted beans.

To the chemist lurking on this forum. Does any of this make sense? Would it make a difference if I used potassium carbonate instead of baking soda to raise my RO water pH? Does baking soda cause the machine to heat faster and possibly explain burning the coffee? Does is explain making it harder to pull on the lever?

Thanks for your input.

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#2: Post by another_jim »

Not a chemist, but ...

The alkalinity (i.e bicorabonate levels) of proper espresso water should be around 75 parts per million. 3 grams in 800 grams of water tots up to around 3500 parts per million,of which around 3000 wll be alkalinity.

I think you may have gone slightly ooverboard, roughly 40 times the amount you should have used.

BTW, the pH of water is extremely variable, depending on CO2 absorbption. It is not a good idea to use it as a measure for mineralizing your water. Google the site for many threads on proper water recipes.
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#3: Post by homeburrero »

Agree with Jim here. You can use a lot of bicarbonate when rinsing a boiler, but for routine brewing that's way way too much. The popular rpavlis recipe for spiking RO with baking soda would be only about 0.08 grams per liter. That is enough to get the pH up above neutral, and give you an alkalinity of 50 ppm as CaCO3. At that level the copper oxide coatings in a brass or copper boiler should be stable.
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bobsy (original poster)
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#4: Post by bobsy (original poster) »

Thanks Jim. The only reason I'm focusing on the pH part is to avoid the copper leaching which - by my understanding - was caused by the low pH of the RO water. Is that not the case? Or did I misunderstand your last sentence?

I did try the rpavlis solution but I still got copper leaching. I will progressively try lower dosage and see if pH is still in the 7 range, and observe if the issues I mentioned with the pull are still there with lower baking soda concentrate.

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#5: Post by Sugarbeet replying to bobsy »

I agree with the others not much bicarb is required to prevent copper leeching. PH is not a great indicator for another reason. Copper dissolves slightly in water even at neutral pH if the water is very soft (around 1~2 micrograms per liter if the entire boiler holding it was from pure copper and the water was completely deionised).

How do I know this? There are few articles about it online, but I had a misfortune of "discovering it" myself when I put a shiny nickel component in contact with distilled water in contact with copper. I had my nickel component plated with thin layer of copper within few days.... Then after cleaning, I added "half a pinch" of bicarb to this distilled water (2l) and the problem went away. This is not drinking water however.