Today in 1983, US Patent 4383040 A was issued, an invention of Richard Fricker, for his “Fermentation Process and Apparatus.” Here’s the Abstract:

A method for continuous fermentation in which carbohydrate solution is fed continuously into a fermentation zone containing substantially homogeneously distributed yeast and carbohydrate solution whereby the carbohydrate is fermented to ethanol, a proportion of the fermenting liquid continuously passing to a pressurized settling tank, yeast depleted liquid being withdrawn from the upper part of the settling tank and yeast enriched liquid being withdrawn from the lower part of said tank and returned to the fermentation zone, a proportion of yeast being withdrawn without being returned to the fermentation zone, said proportion being such that the concentration of yeast in the fermentation zone is substantially constant, and the pressure within the settling tank is sufficient to prevent the formation of gaseous carbon dioxide. The method enables rapid continuous fermentation to take place using high concentrations of yeast.