Phosphate-based acid-reacting compounds are major constituents of chemical leavening, which also contain gas-releasing compounds such as sodium bicarbonate. The aim of this study was to review phosphate-free leavening acids according to the patent literature, a source of information that is rarely cited. Not less than 65 phosphate-free acids were mentioned in patent specifications on chemical leavening that were filed between 1836 and 2021; most of these novel acid-reacting materials were first introduced in letters patent for inventions, 138 in total. Inventors had more interest in tartrates, lactates, sulphates and lactones. In the recent years, there has been renewed interest for highly wholesome, nonsynthetic, aluminium-free, phosphate-free and sodium-free baking powder formulations that would not impart offtaste to bakery foods. Acid-free activating materials such as calcium chloride have been proposed to reduce the level of chemical leavening in bakery foods and improve their flavour.