For example, research on the lactic acid bacteria, which have a dominant role in the production of many fermented foods, particularly those that are milk-based, has continued to advance at a very impressive rate through the 20th century and our understanding of, and ability to manipulate and control these bacteria is now at a level that would have been unimaginable even 20 years ago. This explains, in part, how it is possible to process millions of litres of milk into cheese in a single day in a controlled method where product of the highest quality can be consistently produced.