A coffee machine, comprising: a pot liner, wherein the pot liner has a water inlet and a water outlet; a heating mechanism for heating the pot liner, and an automatic drain mechanism at the water outlet of the pot liner, for opening or blocking the water outlet according to an ambient temperature at the water outlet; a manual exhaust mechanism in a side wall of the pot liner and adjacent to the water inlet, wherein the manual exhaust mechanism comprises: a hollow socket of an exhaust valve extending from the side wall of the pot liner to the external of the pot liner and in communication with the internal of the pot liner; a lid of exhaust valve surrounded by the steam outlet of the socket of exhaust valve; a handle for exhausting steam rotatably fixed at a fixed distance relative to the socket of exhaust valve; wherein an arc edge of the handle for exhausting steam, for contacting the lid of exhaust valve is bias relative to the rotation centre of the handle for exhausting steam, and the lid of exhaust valve is configured to block the steam outlet of the socket of exhaust valve under the force from the handle for exhausting steam when the handle for exhausting steam is rotated to the first position, and the lid of exhaust valve is configured to open the steam outlet of the socket of exhaust valve when the handle for exhausting steam is rotated to the second position; and characterised by: a groove on the handle for exhausting steam, for reducing the maximum force on the lid of exhaust valve, applied by the handle for exhausting steam, when the handle for exhausting steam is rotated to the first position. a pot liner, wherein the pot liner has a water inlet and a water outlet; a heating mechanism for heating the pot liner, and an automatic drain mechanism at the water outlet of the pot liner, for opening or blocking the water outlet according to an ambient temperature at the water outlet; a manual exhaust mechanism in a side wall of the pot liner and adjacent to the water inlet, wherein the manual exhaust mechanism comprises: a hollow socket of an exhaust valve extending from the side wall of the pot liner to the external of the pot liner and in communication with the internal of the pot liner; a lid of exhaust valve surrounded by the steam outlet of the socket of exhaust valve; a handle for exhausting steam rotatably fixed at a fixed distance relative to the socket of exhaust valve; a hollow socket of an exhaust valve extending from the side wall of the pot liner to the external of the pot liner and in communication with the internal of the pot liner; a lid of exhaust valve surrounded by the steam outlet of the socket of exhaust valve; a handle for exhausting steam rotatably fixed at a fixed distance relative to the socket of exhaust valve; wherein an arc edge of the handle for exhausting steam, for contacting the lid of exhaust valve is bias relative to the rotation centre of the handle for exhausting steam, and the lid of exhaust valve is configured to block the steam outlet of the socket of exhaust valve under the force from the handle for exhausting steam when the handle for exhausting steam is rotated to the first position, and the lid of exhaust valve is configured to open the steam outlet of the socket of exhaust valve when the handle for exhausting steam is rotated to the second position; and characterised by: a groove on the handle for exhausting steam, for reducing the maximum force on the lid of exhaust valve, applied by the handle for exhausting steam, when the handle for exhausting steam is rotated to the first position.