When producing yoghurt and certain milk products bacterial cultures are used. The bacteria in question are special kinds of lactic bacteria. They bring about specific biochemical processes which transform ordinary milk into the respective product. As the dairy product to be produced may be negatively affected by unwelcome germs, become inedible or undrinkable or even unhealthy, the lactic bacteria culture must be free from any germs, other cultures and harmful substances. The cultivated lactic bacteria are sold to the dairy industry and used there accordingly. As a consequence the whole application and all the components used must be minimal deadleg.