Abstract: A process for adjusting the amount of yeast introduced into a fermentative liquid comprises periodically taking a sample from a mass of suspended yeast maintained in movement in a closed circuit, subjecting the sample to fermentation by adding a nutrient element, and adjusting the supply of yeast to the liquid in accordance with the fermentative power of the treated yeast sample. The implementing plant comprises a container having a conical bottom containing yeast suspended in a liquid, a pipe connecting the bottom of the container to a fermentation tank, and a regulating or adjusting pump for supplying yeast from the container into the tank. A pipe for recycling the suspended yeast in the container is provided, as well as means for ensuring, during a predetermined time interval, the recycling of the suspension of yeast from the bottom of the container to the upper part thereof.