Abstract: Beer fermentation apparatus comprises a main pipe for transporting a water-entrained mixture of wort, yeast and gas to a fermentation tank. A measuring device is mounted in a by-pass circuit of the main pipe for measuring the amount of gas dissolved in the water, the device comprising a vertically disposed measuring chamber having an inlet at its lower end and an outlet at its upper end which are connected to upstream and downstream portions of the main pipe for flowing the mixture through the measuring chamber. The chamber inlet is located a sufficient distance above the lowermost end of the chamber so as to effect formation of a relatively stagnant flow region which is substantially free of gas bubbles in the measuring chamber beneath the level of the inlet during flow of the water-entrained mixture through the measuring chamber.