Water temperature and ratios

My everyday starting point is a ratio of about 1:16, which means 15 grams of coffee to 240 grams of water. Anything from 1:15 to 1:17 is a reasonable range. I weigh both on a kitchen scale, since scoops vary a lot with roast and grind.

Temperature

The usual guidance is water between about 195 and 205 °F (90 to 96 °C). In practice I use water just off the boil for light roasts, which are dense and harder to extract, and let the kettle rest a minute or two for darker roasts, which can turn harsh with very hot water.

The bloom

I start by pouring roughly twice the coffee's weight in water, about 30 grams, just enough to wet all the grounds, and wait 30 to 45 seconds. Fresh coffee releases carbon dioxide and puffs up during this time. After the bloom I pour the rest in two or three slow pulses, keeping the water level steady instead of flooding the cone.