The polysaccharide Pasteur discovered as a microbial product in wine was dextran. It is a complex, branched glucan: a polymer made from glucose units, with a backbone dominated by alpha-1,6 glycosidic linkages and branches commonly involving alpha-1,3 linkages.
Dextran formed part of Pasteur’s broader investigation of fermentation and wine spoilage. He showed that microorganisms could produce substances that changed the texture and chemistry of wine, helping undermine the idea that fermentation was merely a straightforward chemical process. The discovery linked visible changes in food and drink to microbial activity.
Dextran is not the same as starch, cellulose, or glycogen, despite all four being glucose-based polysaccharides. Their bonding patterns and branching differ. Today, dextran is produced industrially by certain bacteria, including Leuconostoc mesenteroides, and has applications such as plasma-volume expansion and laboratory chromatography. It can also contribute to dental plaque and create problems in sugar refining by increasing viscosity.