It only takes a very small pinch, speaking from experience. Like less than an eighth of a teaspoon will almost eliminate the bitterness in a large mug of coffee, without adding a salty taste.

At least to my tastes, but then I'll literally eat coffee beans so my scale for that may be a bit skewed, though if you drink black coffee already you're probably similarly acclimated to it. It wipes out that sort of sour-bitterness coffee can have, which is the specific thing I find unpleasant in black coffee myself.