Nowadays, yeast is generally produced on an industrial scale. The necessary biotechnological plant (bioreactors) must be fully suited to the physiological requirements of yeast metabolism in respect of substrate feed, aeration, temperature, and pH control. The basic substrate used in the production of yeast is molasses, a byproduct of sugar manufactured from cane and beets.
The influence of aeration
Optimal process utilization of the substrate is only possible if the supply of oxygen is adequate. Too rapid the addition of substrate (e.g. molasses) can lead to so-called catabolite repression and a ”switch” to anaerobic fermentative metabolism, with an unintentional formation of ethanol. However, even correct dosing of molasses does not rule out such an effect, since inadequate supply of oxygen is the most sure and direct way to alcohol fermentation. What is a welcome factor in breweries is detrimental to yeast production, resulting in a substantial loss in yield.
Inadequate oxygen supply is also responsible for a higher level of pollution in the (fermentation) waste liquor, since during subsequent downstream separation processes, the effluent fraction contains a substantially higher proportion of (aerobically) non-degraded nutrients. ”Over-aeration” of the fermenter would certainly be one way of ensuring an adequate supply of oxygen, on the other hand it would drive up energy costs considerably.