Very lightly roasted coffee requires a low dose and a high water ratio (as above). If you add a lot of milk, as most people do with flat whites, lattes, and cappuccinos, then the light, delicate flavor notes, fruits, acidity, and aromas of a lightly roasted coffee can easily be overwhelmed. Replacing a proportion of the milk with some hot water will bring out the full range of flavors from your coffee beans. This hot water has bypassed the coffee extraction bed (to avoid over-extraction bitterness) – hence the term bypass. Commonly, bypass is used with Americanos and long blacks. But with an increasing trend to lighter roasted coffee, bypass should also start to be included with milk versions.

At the other end of the roast/density spectrum, a very dark roasted bean can be very ashy and burnt-tasting. A large volume of milk helps make a more palatable drink; no bypass hot water is required.

Your coffee is likely to be roasted somewhere between these extremes. The optimum bypass hot water for your roast level will fall on this scale.