Today in 1939, US Patent 2155134 A was issued, an invention of Walter Karsch, for his “Fermentation Process.” There’s no Abstract, although in the description it includes this summary:

This invention relates to a fermentation process for the production of alcohol from liquids containing carbohydrates.

The invention provides that the total quantity of yeast shallrbe led positively and continuously in a circuit through a fermentation system consisting of a mixing device and a separating device in this wise that the total quantity of .yeast is moved unidirectionally from the mixing device to the separating device and back to the mixing 5 device. Preferably, after a predetermined controllable time, each yeast particle passes through the separating device and thus comes in contact, with fresh particles of sugar. The yeast is thus for a short time only free from the material to be fermented. The fermented liquor, after a predetermined controllable time, and after once traversing the fermentation system, leaves the said system beyond the separating device. It has been found that yeast can operate continuously in this process because it is removed as rapidly as possible from the conversion products formed. The loss of yeast cells observed with discontinuous fermentation practically does not occur in the present process. The mixing oi the yeast and of the liquor to be fermented is as intimate as possible, so that the conversion of the sugar to alcohol and to carbonic acid is effected with the greatest rapidity. At the exchange surface–the yeast membranes-by the intimate admixture the conversion products formed are withdrawn and new sugar molecules added.

By the flow through the fermentation system in the direction from the mixing device to the separating device it is further ensured that each yeast particle is separated positively after a predetermined time from the conversion products and is mixed with fresh sugar particles. No yeast particles can move in the fermentation system otherwise than in the desired direction, or settle, which is of great importance for the attainment of a maximum output of alcohol. Likewise the fermented liquor is led positively to the separating device, so that the result is obtained that the nocuous conversion products formed are separated as soon as possible from the yeast.

In the preferred embodiment the liquor is subjected to an after-fermentation in the interval between the mixing of the yeast with the liquor to be fermented and the separation of the yeast from the fermented liquor.