Quotes from James Hoffman

Excellent coffee should have its own sweetness, and instead of suppressing bitterness the milk will obscure the flavour characteristics of the coffee, hiding the work of the producer and the expression of terroir that the coffee has.

typically a cup of brewed coffee is 1.3–1.5 per cent dissolved coffee and the rest is water. With espresso, the ratio may be closer to 8–12 per cent dissolved coffee.