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Your biology book says enzymes are proteins that speed up reactions in cells. That sounds obvious now. In the 1890s it was an open question whether the chemistry of life could happen at all outside a living cell. Eduard Buchner answered it with yeast, sand and a hydraulic press. This post covers what he did, the checks that made his result convincing, a worked calculation on the reaction he studied, and the part he got wrong.
What was the argument about?
In his Nobel lecture of 1907, Buchner sets out the background. By the 1830s researchers had shown that yeast is made of living cells. Louis Pasteur's experiments then led to the view that "in Nature without living organisms, without live yeast, no fermentation exists." Others thought a chemical substance inside the yeast did the work, but every attempt to separate one had failed. Pasteur himself wrote that he could neither accept nor reject that idea. Our post on Louis Pasteur and fermentation covers his side.
How did Buchner get the juice out of yeast?
Yeast cells are tiny and have tough walls. Buchner's lecture describes the method that worked. He mixed yeast with one part quartz sand and one-fifth part diatomite (kieselguhr) by weight, ground it in a large mortar for a few minutes until it became a dark-grey dough, wrapped it in canvas and squeezed it in a hydraulic press. "Within a few hours 500 cc of liquid can be obtained from 1000 g of yeast." He credits Martin Hahn, then assistant to his brother Hans, with proposing the diatomite and the press.
It was not a straight road. The Nobel biography records that his first experiments on breaking yeast cells were made in 1893, but the laboratory board decided that "nothing will be achieved by this," and the work was set aside for three years. He restarted in autumn 1896 at the Hygienic Institute in Munich. On 9 January 1897 he sent his first paper, Alkoholische Gährung ohne Hefezellen (alcoholic fermentation without yeast cells), to the Berichte der deutschen chemischen Gesellschaft.
Why was the result convincing?
Adding sugar to fresh juice produced a steady stream of carbon dioxide, and the alcohol formed in the same proportions as with live yeast. The obvious objection was that a few living cells had slipped into the juice. Buchner's lecture lists the checks he ran against that:
The juice still worked after being filtered through diatomite and even through porcelain filter candles.
Toluene stops live yeast fermenting sugar, but it did not stop the juice.
The juice could be dried to a powder in a vacuum, and the powder still fermented sugar.
Yeast killed with alcohol or acetone, so it could no longer grow, still caused "an extraordinarily powerful fermentation."
He concluded that the active agent was "a chemical substance, an enzyme, which I have called 'zymase'." The Nobel Prize summary puts the consequence plainly: biochemical processes "do not necessarily require living cells, but are driven by special substances, enzymes, formed in cells."
A worked example: how much alcohol and carbon dioxide?
The overall equation for alcoholic fermentation is:
C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂
Using C = 12.011, H = 1.008, O = 15.999:
Glucose: 6(12.011) + 12(1.008) + 6(15.999) = 180.16 g/mol.
Two moles of ethanol: 2 × 46.07 = 92.14 g.
Two moles of carbon dioxide: 2 × 44.01 = 88.02 g.
Check: 92.14 + 88.02 = 180.16 g. Mass is conserved.
So 100 g of glucose gives at most 51.1 g of ethanol and 48.9 g of carbon dioxide. That matches Buchner's report that in cell-free fermentation "alcohol and carbon dioxide were produced in equal weights", which is nearly but not exactly true. He also found that some sugar ended up in other products, so real yields were lower than this maximum.
A common mistake is to write C₆H₁₂O₆ → C₂H₅OH + CO₂ and forget the 2s. Always count atoms on both sides before you use an equation for a calculation.
What did Buchner get wrong?
In the same lecture Buchner argued that lactic acid, or something close to it, was an intermediate on the way from sugar to alcohol. Later work showed a different route. The NCERT Class 11 chapter Respiration in Plants gives the accepted picture: in yeast, glucose is broken down to pyruvic acid by glycolysis, and pyruvic acid is converted to CO₂ and ethanol by the enzymes pyruvic acid decarboxylase and alcohol dehydrogenase. Lactic acid is made from pyruvic acid by some bacteria and by muscle when oxygen runs short.
Being wrong about the pathway did not undo his main result. It is a good reminder that a discovery and its first explanation are separate things.
If enzyme ideas such as active sites and inhibition are still hazy, the Fermi Concept Library covers every concept in biology and chemistry, each with its own lesson, and our enzymes post has worked kinetics questions.
How did his life end?
The Nobel Prize biography records that Buchner served in a field hospital in Romania during the First World War, was wounded, and died on 13 August 1917, aged 57.
What can a student take from Buchner's way of working?
Return to a shelved idea. His crushing experiments were stopped for three years and then succeeded.
List the alternative explanations and test each. That is what turned a bubbling liquid into evidence.
Separate what you observed from how you explain it. His observation stood; his lactic acid pathway did not.
Write the fermentation equation from memory tonight, balance it, and check the masses add up to 180 g.
