Copy of a grape vine with two bunches of grapes, one wrapped in cotton wool, the other exposed, to illustrate an experiment performed by Pasteur on the fermentation of grape juice
This model illustrates an experiment performed in 1862 by Louis Pasteur (1822-1895) to study the fermentation of grape juice. One bunch of grapes is wrapped in sterilised cotton wool while the other is exposed to the air. When both bunches were ripe, they were crushed separately in vessels – those from the covered bunch did not ferment but the uncovered ones did. This experiment showed that alcoholic fermentation only happens when the grape juice comes into contact with germs of yeast in the air. This experiment was one of a series by Pasteur that disproved existing ideas about spontaneous generation.