A beer maker comprising: a fermentation tank assembly including a fermentation tank having an opening formed therein and a fermentation tank cover for opening/closing the opening, the fermentation tank assembly is adapted to accommodate a beer brewing pack insertable in the fermentation tank through the opening; a gas extraction flow path connected to the fermentation tank assembly; and a gas opening/closing valve disposed in the gas extraction flow path, characterized in that the beer maker further comprises: a pressure sensor disposed prior to the gas opening/closing valve along the direction in which gas from the fermentation tank is discharged configured to sense a pressure of the gas discharged from the beer brewing pack; and a controller configured to calculate a fermentation degree based on a pressure sensed by the pressure sensor and to control the gas opening/closing valve, if a variation in pressure sensed by the pressure sensor is equal to or less than a reference value after fermentation is initiated, the controller is configured to: open the gas opening/closing valve; complete primary fermentation performed in a state in which the gas opening/closing valve is open; close the gas opening/closing valve; and initiate secondary fermentation performed in a state in which the gas opening/closing valve is closed. a fermentation tank assembly including a fermentation tank having an opening formed therein and a fermentation tank cover for opening/closing the opening, the fermentation tank assembly is adapted to accommodate a beer brewing pack insertable in the fermentation tank through the opening; a gas extraction flow path connected to the fermentation tank assembly; and a gas opening/closing valve disposed in the gas extraction flow path, characterized in that the beer maker further comprises: a pressure sensor disposed prior to the gas opening/closing valve along the direction in which gas from the fermentation tank is discharged configured to sense a pressure of the gas discharged from the beer brewing pack; and a controller configured to calculate a fermentation degree based on a pressure sensed by the pressure sensor and to control the gas opening/closing valve, if a variation in pressure sensed by the pressure sensor is equal to or less than a reference value after fermentation is initiated, the controller is configured to: open the gas opening/closing valve; complete primary fermentation performed in a state in which the gas opening/closing valve is open; close the gas opening/closing valve; and initiate secondary fermentation performed in a state in which the gas opening/closing valve is closed. a pressure sensor disposed prior to the gas opening/closing valve along the direction in which gas from the fermentation tank is discharged configured to sense a pressure of the gas discharged from the beer brewing pack; and a controller configured to calculate a fermentation degree based on a pressure sensed by the pressure sensor and to control the gas opening/closing valve, if a variation in pressure sensed by the pressure sensor is equal to or less than a reference value after fermentation is initiated, the controller is configured to: open the gas opening/closing valve; complete primary fermentation performed in a state in which the gas opening/closing valve is open; close the gas opening/closing valve; and initiate secondary fermentation performed in a state in which the gas opening/closing valve is closed. open the gas opening/closing valve; complete primary fermentation performed in a state in which the gas opening/closing valve is open; close the gas opening/closing valve; and initiate secondary fermentation performed in a state in which the gas opening/closing valve is closed.