Abstract: During baker’s yeast manufacturing, the fermentation process must be thoroughly controlled. This review ofthe patent literature provides new information on the early development of industrial fermentation processes. As shownby a review of 199 patents filed between 1900 and 2009, inventors in this field were mainly interested to improve yeastyields through the control of infection and sugar concentration in the growth media. Contrary to common belief, muchattention was also given to continuous culture processes, involving addition and withdrawal of growth media. Thesetechnologies were mainly developed in about 30 y, between 1910 and 1939. In the recent years, inventors gave sustainedattention to the fine tuning of fermentation control, mainly the rapid determination of yeast fermentation by-products inthe exhaust to get rapid feedback on the rate of sugar addition in the fermentation tank. Improved fermentation controlbenefited much the baking industry because baker’s yeast had higher gassing power and was cheaper. However, some ofthese key patents on baker’s yeast technology were later declared invalid in court because it had little intellectual propertyvalue. In the baker’s yeast trade and other sectors, this situation might have encouraged trade secrets while reducing thecredibility of innovative ideas disclosed in the patent literature.Keywords: baker’s yeast, bread, fermentation control, patents, sugar