Everyone’s idea of the perfect cup of coffee is different. Whether you have yours black, with a splash of milk or extra sweet, you like it your way. But is there a universal law that governs how that flavor gets into your cup? According to new research published in the journal Royal Society Open Science, part of the answer lies in the permeability of the puck, the name for the bed of tightly packed coffee grains through which water passes under high pressure.

To make a really good espresso is essentially trial and error. No matter the coffee type, baristas must constantly adjust how finely the coffee is ground and how much is packed into the puck to achieve the right flow rate. This is the volume of liquid passing through the puck over a specific amount of time and determines how long the water stays in contact with the grounds. This new research helps take some of the guesswork out of the process.