GB845315A - Continuous process for the production of yeast - Google Patents

Abstract

In a continuous process for growing yeast e.g. baker's yeast under conditions of aeration, fermentation is effected in two or more, preferably 3 to 6, fermentation vessels, to the first of which is added yeast, nutrients and water, yeast being continually grown and further nutrients and water added to this vessel until the desired quantity of yeast and medium is obtained, whereupon, whilst continuing to grow yeast and add nutrients and water yeast-containing medium is continuously transferred to the second fermentation vessel so as to maintain the yeast cell concentration and volume of medium in the first vessel constant at the desired level, there being then added to the second vessel nutrients and water to grow yeast in it, the volume of medium and yeast cell concentration being kept constant by continuously transferring yeast-containing medium either to a further fermentation vessel or vessels in each of which the same procedure is repeated, or, alternatively, to a ripening vessel in which ripening conditions are maintained and from which yeast cells are subsequently recovered by filtration, the conditions of fermentation and the transfer rate between vessels being so controlled as to provide a rate of yeast production per unit amount of yeast in the range 0,05 to 0,20, most suitably between 0,075 to 0,175. The nutrient is an aqueous solution of molasses, ammonium hydroxide and ammonium sulphate; diammonium phosphate is preferably added to the first vessel only to give yeast containing 2,0 to 2,8% phosphate as P2O5 based on the yeast dry matter. Preferred conditions for all fermentation vessels, except the last, are: temperature 75 DEG to 92 DEG F., pH 3,0 to 5,5, grams assimable nitrogen per 100 grams molasses added 0,50 to 4,0, whereas for the last they are, respectively, 90 DEG to 95 DEG F., 4,5 to 5,5, and 0,0 to 0,07. In the ripening vessel no or fewer nutrients are added and the aeration rate is less than that effected in the fermentation vessels. An alternative starting procedure comprises seeding nutrient medium in the first vessel with yeast, thereafter adding nutrients and water and aerating, and continuing as before. The process may be terminated by either stopping transfer of yeast containing medium between vessels and ripening the yeast in each, or by allowing the vessels to empty themselves commencing with the first. The desirable rate of production of yeast for any vessel when the process is operating steadily and continuously is substantially equal to the maximum rate achieved during starting up in that vessel.