I had a problem with overwhelming acidity of Lavazza Oro coffee out of my ROK GC espresso maker. It was so bad that I almost threw away the whole kilogram of it. That coffee is lightly roasted and ROK's brewing temperature was not helping. Resulting coffee was so sour that it was not drinkable and it was also gushing through the machine for some reason although I ground it the same as other coffees I use regularly.

Then I stumbled upon Mr Hoffmann's video about hacking sour espresso and that gave me idea of adding tiny pinch of baking soda to ground coffee, just before brewing. I simply put very little of it on top of the coffee in portafilter, mixed it and tamped as usual.

Result was that all of the unpleasant acidity was completely gone, gushing stopped, and on top of that was a gorgeous crema.

I cannot detect any detrimental effect of adding little baking soda on coffee aroma. Contrary, it tastes great and the whole bag of Lavazza survived.

Mr Hoffmann suggested making alkaline water to add after brewing but this worked perfectly and it was far simpler to do.

I've done the same with the ROK and tested various amounts of baking soda to see at which point it gets too much but I did find a point where it has a positive impact with more crema and less acidity without an adverse taste of the baking soda. I was testing it with a powerless coffee cart and had it paired with the ROK grinder as well. It's been a while since I've used it but I remember it was hard to dial in the ROK and consistent shots were difficult which I suspect is related to things like water temp and pressure of which a machine can be far more consistent. one of the gears is broken on the ROK grinder that I need to replace, the grinder is surprisingly good but even then I had to push it as fine as it could go to get the point where the ROKpresso performed well which I felt was a little frustrating.