I checked his numbers, and they check out close enough. I got 1.0 mmol/l for magnesium sulfate and 1.01 mmol/l for sodium bicarbonate, which would be a total hardness of 100mg/l and total alkalinity of 50mg/l. (or GH:KH of 100:50 in common parlance.)
I've noticed a few folks on his Barista Hustle slack going with similar recipes and liking the taste.
Since it's all Mg++, and there is no calcium hardness, The typical scaling factor calculations don't apply here. It would produce no CaCO3 scale, and I think
there should be no magnesium deposits causing problems at this level.
Only concern re machine health might be the corrosivity. The sulfate concentration of that recipe is 91 mg/l, and sulfates are associated with corrosion. At that level, and with an alkalinity of 50 mg/l, I don't think it's a problem unless you have a vintage machine and are extremely cautious about any potential of corrosion. (Maybe we can have a chemist, like rpavlis, weigh in about that.)
jonr wrote:Which bicarb?
I suspect that using any amount of tap water adds a variable. Ie, tap water can change.
He says he uses distilled, and doesn't say which bicarb, but I'm sure it's sodium bicarb, because the numbers come out right when you assume that.