the time it takes to heat X-amount of liquid (and thus, the 'recommended amount' of power) depends on the wattage of the heater, and the size of the brew. If you were brewing 1 ounce of beer at a time, a 50 watt induction coil would be more than you would ever need...
But, you didnt define the amount of liquid you are trying to heat, so its not possible to define how much power you would need to heat that unknown amount of liquid 'in a reasonable amount of time'....
kidding aside, remember that a "1000 watt" induction cooker usually means "...it pulls 1000watts of electricity from the wall";
NOT "...it supplies 1000w of equivalent heat to the water in the pot".
comparatively, a 1kW water heating element DOES provide nearly the full 1kW to the pot due to direct contact between the water and the heat source, which provides nearly 100% efficient transfer of energy....
induction cook tops are usually 20-50% efficient (rarely higher, sometimes even lower), which greatly depends on how well the coil can electrically couple to the pot, so take that into consideration. a "1000w" induction cook top may only be equivalent in performance to a 200-500w water heater element, **while still consuming the same amount of electrical power** as the water heater element (hence induction "efficiency" is lower).