What do the three numbers of espresso stand for?

The three numbers of espresso represent the degree of roasting. According to relevant data, the shell of espresso coffee cup is printed with three numbers: 1, 3 and 5, which are named after the baking degree respectively. 1 stands for 30% roast degree, with slightly bitter and slightly sour taste, while 5 stands for 50% roast degree, slightly bitter and not sour, so three numbers of espresso represent roast degree.