Another way to reduce the acidity is to mix in ground up egg shells into the ground coffee. As you brew this mixture, the calcium carbonate of the egg shells (a

Another way to reduce the acidity is to mix in ground up egg shells into the ground coffee. As you brew this mixture, the calcium carbonate of the egg shells (alkaline) partially neutralises the acids from the coffee beans. You can even combine this with the two usual methods for low acidity coffee that you mentioned (cold brewing and using dark roasts). I haven't actually tried this combo yet but I'm keen to!