In the field of microorganisms, genetic engineering techniques suitable for food production are mainly used for bacteria (such as starter cultures for dairy products and enzyme production) and yeast fungi (e.g. in brewing beer).

In cheese production, the use of the genetically engineered enzyme chymosin has now become established. To turn milk into cheese, rennet, which is traditionally obtained from calves' stomachs during slaughtering, is added to work as a thickening agent. The main agent in rennet is chymosin. At present, there are no recognised methods available for the detection of genetically modified chymosin in whey.

The use of genetically modified yeast or genetically produced enzymes is also conceivable in brewing beer. For beers brewed according to the German purily law of 1516, which prescribes that beer may only be made from the ingredients water, hops, malt and yeast, the direct use of genetic engineering processes is currently excluded. In Germany, the use of isolated enzymes in the brewing process is not permitted. If enzymes are used in foreign beers, they may be genetically engineered. Modifications – this also applies to genetic engineering processes – to the yeast to increase performance, on the other hand, are compatible with the purity law. Various genetically modified yeasts have been developed to the point where they are ready for use in industry, especially for low-alcohol or low-calorie beers, but they have hardly been used so far since German breweries plan to avoid them to brew in conformity with the purity law.

Details on the German purity law and the use of genetic engineering in the process of brewing beer can be found here, for instance: