The flotation process, if properly carried out, aerates the wort sufficiently to ensure an adequate supply of oxygen for the pitching yeast while removing 50 to 60% of the cold break. A new air injector, designed to facilitate the optimization of both aspects of flotation, is described. Since the solubility of the oxygen contained in air injected into wort depends on the size and number of bubbles as well as the difference between the oxygen concentration in air (about 21%) and the concentration of dissolved oxygen already in the wort, the maximum dissolved oxygen level achievable by air injection is limited, and can only be exceeded by injecting pure oxygen (which, however, entails a certain risk of overdosing, since oxygen concentrations above 30 mg/litre can be harmful to yeast). The principle of the separation of cold break during flotation, whereby particles become attached to rising air bubbles and are carried to the surface, is explained. The new injector produces very fine bubbles, thereby increasing oxygen solubility and, by limiting the size of the particles which can be raised to the surface, prevents the loss of yeast cells during flotation without impeding the removal of the much smaller particles making up the fine fraction of the cold break. Where extra oxygen is required (e.g. at higher wort gravities) the air can be supplemented with pure oxygen before injection, allowing the necessary oxygen level to be achieved with the minimum consumption of pure bottled oxygen (much more expensive than air, even if the cost of air sterilization is included) and without any risk of excessive oxygenation.
Keywords : aeration break cold equipment flotation oxygen pitching yeast separation wort