A small volume bioreactor comprising a cultivation vessel that - has a working volume of from 20 ml to 350 ml, - comprises a stirrer shaft with at least one impeller affixed thereto, - comprises a feed pipe comprising i) a sparging tube connected to a sparger at its end, and ii) at least one feed line with an opening at its end, - comprises two or more baffles (114; 126) extending from the wall of the cultivation vessel perpendicular in the direction to the center of the cultivation vessel , and - a reactor head plate , wherein the reactor head plate comprises - a fitting for connecting the drive axis of a motor to the stirrer shaft , - a sparger gas inlet connected to the sparging tube in the feed pipe , optionally a gas inlet connected to the headspace , - a gas outlet connected to the headspace of the cultivation vessel , - at least one inlet for liquids of a feed line being part of the feed pipe , - one in-situ sensor port with a pH electrode mounted thereto, and - a supply port area comprising the sparger gas inlet and the inlet of the at least one feed line , wherein the cultivation vessel and the reactor head plate are both substantially made of non-metal material, whereby the small volume bioreactor comprises an in-situ glucose sensor. a cultivation vessel that - has a working volume of from 20 ml to 350 ml, - comprises a stirrer shaft with at least one impeller affixed thereto, - comprises a feed pipe comprising i) a sparging tube connected to a sparger at its end, and ii) at least one feed line with an opening at its end, - comprises two or more baffles (114; 126) extending from the wall of the cultivation vessel perpendicular in the direction to the center of the cultivation vessel , and - a reactor head plate , - has a working volume of from 20 ml to 350 ml, - comprises a stirrer shaft with at least one impeller affixed thereto, - comprises a feed pipe comprising i) a sparging tube connected to a sparger at its end, and ii) at least one feed line with an opening at its end, - comprises two or more baffles (114; 126) extending from the wall of the cultivation vessel perpendicular in the direction to the center of the cultivation vessel , and - a reactor head plate , wherein the reactor head plate comprises - a fitting for connecting the drive axis of a motor to the stirrer shaft , - a sparger gas inlet connected to the sparging tube in the feed pipe , optionally a gas inlet connected to the headspace , - a gas outlet connected to the headspace of the cultivation vessel , - at least one inlet for liquids of a feed line being part of the feed pipe , - one in-situ sensor port with a pH electrode mounted thereto, and - a supply port area comprising the sparger gas inlet and the inlet of the at least one feed line , - a fitting for connecting the drive axis of a motor to the stirrer shaft , - a sparger gas inlet connected to the sparging tube in the feed pipe , optionally a gas inlet connected to the headspace , - a gas outlet connected to the headspace of the cultivation vessel , - at least one inlet for liquids of a feed line being part of the feed pipe , - one in-situ sensor port with a pH electrode mounted thereto, and - a supply port area comprising the sparger gas inlet and the inlet of the at least one feed line , wherein the cultivation vessel and the reactor head plate are both substantially made of non-metal material, whereby the small volume bioreactor comprises an in-situ glucose sensor. <EOS>