From yeasts to wine
It was in the seventeenth century when the yeasts were first observed by Antoni van Leeuwenhoek. He perfected microscopes and started a scientific revolution with the discovery of microbial life. He also looked for the first time at sperm, red blood cells, plant cells and various inorganic materials. By the way, when he saw the yeasts in the brewing of bread, he thought that they were tiny, inert, inorganic grains responsible for the fermentation of the beverages and the lifting of the bread. The Latin word levare means “to lift”, hence its name.
In the following century, the 18th century, with the works of the French chemist Antoine Lavoisier and his wife Marie-Anne Pierrette, it became more or less clear that during fermentation the sugars are converted into alcohol and carbon dioxide (do you remember the bubbles?). They knew that the yeasts, that strange microscopic and “inert” substance, was necessary to start the fermentation, but they did not know why. Then came another French chemist, Joseph Gay-Lussac, and warned that grape juice does not ferment when boiled unless they introduced yeast. The importance of yeast was clear, but: What was its role there, in the beverage?
Now it’s 1835 and we’re still in France. The physicist and engineer Charles Cagniard de la Tour observed that yeasts multiply by budding during the fermentation. In the budding, the mother yeast emits a bulge that will later become yeast. It is like if children sprout from the skin (Do you remember the Gremlins? Well, something like that). This discovery allowed us to recognize them as living entities and paved the way to finally explain the role of yeasts in fermentation.
The great Louis Pasteur came in the mid-1800s and proved , for the first time, that yeasts are the ones that transform the juice of grapes into wine. They do it in the absence of oxygen (hence the sealed containers), transforming the sugars of fruits in alcohol.
Glycolysis and wine
Since the 20th century, the scientists recreate the fermentation in vitro using the cellular content of yeasts. Eduard Buchner was the German chemist who dried, crushed and macerated yeast to release its contents; a kind of yeast juice. He added glucose to that preparation and observed that it produced bubbles and alcohol. He postulated the existence of a “zymase”, a substance inside the yeast responsible for carrying out the transformation of sugar. In 1907 he received the Nobel Prize in Chemistry for his discovery.
The biochemist elucidated the nature of the “zymase” little by little. In 1940, they described the complete biochemical process. Zymase was actually a group of several different enzymes. The activities provide energy for the yeast in 10 sequential chemical reactions: glycolysis. This biochemical process is common in almost all living beings. Only in animal cells does not end with the release of alcohol (thank goodness), but a molecule called pyruvate.
Nowadays, the scientists put interest in obtaining better strains of yeast. Improved strains provide distinction to the wines through controlled fermentation. But also they put interests in the improvement of conventional vines through plant breeding.
Besides, a better understanding of the historical join between grapes and yeasts has been key to consolidate and improve the wine industry. And the discoveries do not stop.
Speaking of company and wine…
In 2014, Italian scientists published a surprising finding. They study the vine bacterial microbiome. This is the total bacterial community that colonize the vines. One piece of information did not match the microbial composition they expected. They detected the DNA of a bacterium that should not be there. It was like if analyzing photos taken in a tropical forest, we notice the presence of polar bears.
The intrusive bacteria was Propionibacterium acnes, the bacteria responsible for acne. The most logical thing was to think that it was a contamination when handling the samples. For example, the technician could have passed the bacteria from his hands to the samples. Yet, after many analyzes, they ruled out that possibility.
They discovered that this Propionibacterium acnes is not able to grow outside the plant. It is an obligate endophytic bacterium. It lives only in the internal tissues of the vine. It accumulates many mutations that hinder its ability to survive as an autonomous microorganism. (I wrote about endophytic bacteria in Bacteria For Feeding The World).
The original version of this post was in Spanish and published in Persea Magazine as El vino es mejor en compañía.
To learn more: Alba-Lois y Segal-Kischinevzky. (2010). Yeast fermentation and the making of beer and wine. Nature Education, 3(9), p. 17. Chambers y Pretorius. (2010). Fermenting knowledge: the history of winemaking, science and yeast research. EMBO reports, 11(12), pp. 914. Campisano et al. (2014). Interkingdom transfer of the acne causing agent, Propionibacterium acnes, from human to grapevine. Molecular Biology and Evolution, 31(5), pp. 1059-1065.