In the 19th century people believed fermentation was a special life process possible only inside living cells. Buchner ground yeast with sand and filtered it to obtain a cell-free “yeast extract.” When he added sugar, the liquid still produced carbon dioxide and alcohol. This proved that chemical reactions could proceed outside the cell and that a catalyst—later called an enzyme—was responsible. His result demolished vitalism and opened the field of biochemistry. The principles he uncovered are now applied in drug manufacturing and biofuel production.

In 1897 Buchner ground baker’s yeast with quartz sand, added magnesium sulfate, and pressed the mash to obtain a nearly cell-free ‘press juice’. Confirmed to be sterile, the extract produced CO₂ and ethanol from sucrose in a temperature- and pH-dependent fashion. He named the catalytic factor “zymase,” anticipating protein catalysts we now call enzymes. The work shattered Pasteur’s vitalist view and stimulated enzyme purification, Michaelis-Menten kinetics, and elucidation of the Embden–Meyerhof glycolytic pathway. It also supplied the theoretical basis for process optimization in brewing and food industries, laying a cornerstone of modern biotechnology.

Buchner’s method, combining mechanical disruption with osmotic shock, pioneered modern cell-free extract preparation. Activity was destroyed by heating to 60 °C, indicating a thermolabile protein catalyst. Using gas volumetry he quantified CO₂ evolution and its proportionality to substrate concentration, and employed acid or heat inhibition to probe specificity. Zymase was later resolved into multiple enzymes such as hexokinase, phosphofructokinase, and pyruvate decarboxylase. By enabling in-vitro reconstitution and pathway analysis, the work launched enzymology and metabolic engineering. Treating catalytic proteins quantitatively fostered Sumner’s enzyme crystallization and Michaelis–Menten kinetics, and even influenced early industrial scale-up of ethanol fermentation.