Coffee should do not percolate for more than five minutes. If percolating on the stove, as soon as the coffee begins to percolate, turn the heat down to low and allow it to continue percolating for three to five minutes.
The coffee gets progressively darker as it splashes up into the clear knob at the top of the coffee pot. The color helps determine the strength and doneness of the coffee. The darker the color, the stronger the coffee. Stop percolating when reaching the desired color, and allow the coffee to cool down on another burner to stop the cooking process.