The French scientist Louis Pasteur (1822-1895) reported as early as 1861 that yeasts consume much less sugar during fermentation in the presence of oxygen, i.e. in an aerobic environment, than in an anaerobic environment. However, at higher concentrations of glucose (grape sugar) in the grape must from about 100 mg/l, ethanol (alcohol) can also be formed in the presence of oxygen. The phenomenon is called the "Crabtree effect" (also "Pasteur effect") after the English biochemist Herbert Grace Crabtree. Genetic engineering could be used to develop effect-enhancing yeasts. At low glucose concentrations in the grape must, yeasts directly metabolise the sugar in the presence of oxygen, i.e. it is not converted into alcohol. In Geisenheim, attempts are being made to convert the glucose present in the grape must into gluconic acid by means of the enzyme glucose oxidase. Gluconic acid cannot be converted into alcohol by the yeasts. Similarly, experiments are also being carried out with the selection of ineffective yeasts. These methods are used to produce wines with lower alcohol content with the aim of improving the taste. See alcohol reduction for more details.