Fermented foods have been consumed for more than 10 000 years, making food fermentation probably one of the oldest food technologies implemented by man. Presently, fermented food products are estimated to represent a third of our food intake. The scientific knowledge behind its role and mechanisms of action have only been studied in the past 150 years. Food microbiology has provided many answers behind the roles, modes of action, nutrition, and health effects of fermented foods. Nevertheless, one of the major topics of concern remains the safety demonstration of microbial food cultures. Despite this very long history of traditional use, what is considered fermented in a part of the world is considered spoiled, if not unsafe, in another one. As an example, in late 2017, China blocked the importation of cheeses from Europe due to the presence of microbial food cultures not present in the Chinese 2010 positive list: Penicillium roquefortii, Penicillium camemberti, and the presence in their genomes of mycotoxin genes. This is not unheard of per se, as the Biohazard Panel of the European Food Safety Authority has excluded filamentous fungi from the Qualified Presumption of Safety. The United States (GRAS!– Generally Recognized as Safe) also has a respective procedure in place for the microbial risk assessment of microbial species voluntarily added to the food chain. The International Dairy Federation (IDF), in collaboration with the European Food and Feed Cultures Association, has been working for the past 20 years on an inventory of microbial species with technological properties in fermented foods. Safety demonstration of food and feed cultures through inoculation into a food matrix for use in the food chain is aimed to avoid trade barriers between countries when a history of safe use cannot be established for an indigenous fermented food product on the international market. It is as well important to avoid the pitfalls of cross- over fermentation, when changing the traditional food matrix, and when possible, to also avoid deleterious microbial metabolic activities.