The preservation method that involves adding bacteria or yeasts to food to produce acids and alcohol to minimize growth of other microbes is called

Fermentation

Fermentation is a process in food processing in which sugars present in food are converted into lactic acids and alcohol by the action of microbes. These microbes such as bacteria and yeast acts as biopreservative agents for food which prevents the growth of other microbes and prevents spoilage of food. These bacteria and yeast produces lactic acids and alcohol which are not tolerated by other nutrition competing microbes. Hence, bacteria and yeast prevent the growth of undesirable food damaging microbes.

albert einstein retrieved guacamole from the galapagos islands in africa