A method of controlling a coffee brewing system comprising at least one coffee brewing machine and at least one grinder for grinding coffee beans contained in a reservoir and providing at least one dose of a grind for the coffee brewing machine, which is connected to the grinder via a wired or wireless communication link, comprising the steps of: e1) selecting on the grinder with control members, the type of coffee desired, e2) selecting on the grinder with control members the portion or portions corresponding to the desired number of grind doses, e3) selecting initial operating parameters of the mill, e4) collecting the corresponding quantity of coffee beans from the reservoir and starting the operation of grinding the coffee beans, according to the initial operating parameters of the grinder, in order to provide the grind, e5) using the grinder to transmit to the coffee brewing machine an instruction for activating a control key of said coffee brewing machine, the actuation of said activated key being compatible with the type of coffee and the number of doses of the selected grind, the other control keys of said coffee brewing machine remaining inactivated, e6) measuring the flow time of an amount of water corresponding to the choices made under e1 and e2), through the grind, following the operation of the active control key, e7) comparing the measured value M at e6) with a prerecorded range of reference time values (VR1, VR2) and determining the deviation Δ between the measured value and the reference value if is less than or between and if is greater than, and e8)-e9) controlling the operation of the grinder as a function of the comparison carried out and/or of the deviation (Δ) determined at e7), the control consisting of increasing the quantity of grind by increasing the duration of collecting and grinding the coffee beans if the measured value is less than the first reference value or decreasing the quantity of grind by decreasing the duration of collecting and grinding the coffee beans if the measured value M is greater than the second reference value. e1) selecting on the grinder with control members, the type of coffee desired, e2) selecting on the grinder with control members the portion or portions corresponding to the desired number of grind doses, e3) selecting initial operating parameters of the mill, e4) collecting the corresponding quantity of coffee beans from the reservoir and starting the operation of grinding the coffee beans, according to the initial operating parameters of the grinder, in order to provide the grind, e5) using the grinder to transmit to the coffee brewing machine an instruction for activating a control key of said coffee brewing machine, the actuation of said activated key being compatible with the type of coffee and the number of doses of the selected grind, the other control keys of said coffee brewing machine remaining inactivated, e6) measuring the flow time of an amount of water corresponding to the choices made under e1 and e2), through the grind, following the operation of the active control key, e7) comparing the measured value M at e6) with a prerecorded range of reference time values (VR1, VR2) and determining the deviation Δ between the measured value and the reference value if is less than or between and if is greater than, and e8)-e9) controlling the operation of the grinder as a function of the comparison carried out and/or of the deviation (Δ) determined at e7), the control consisting of increasing the quantity of grind by increasing the duration of collecting and grinding the coffee beans if the measured value is less than the first reference value or decreasing the quantity of grind by decreasing the duration of collecting and grinding the coffee beans if the measured value M is greater than the second reference value.