Tannins are found mostly in red wines, derived primarily from grape skins, seeds and stems, but also from oak barrels. Tannin acts as a natural preservative that helps wine age and develop.
Red wines tend to have higher tannins than white wines due to prolonged exposure of the grapes to the juice which allows the tannin more time to dissolve in the alcohol and water in the wine.
There are also wood tannins that dissolve into wine through contact when wine is aged in wooden barrels. Oak barrels are the most popular choice, and an oak barrel can be used in winemaking for up to 70 years.
The chemical composition of these tannins are actually changed during the winemaking process.
According to Dr Paul Smith, a chemist at the Australian Wine Research Institute, “Wine tannins constitute evolved grape tannins plus some grape tannins in the same chemical state as they were in the grape.”
Dr Leigh Francis, also of the AWRI, expands on this: “Wine tannins are considered more complex than grape tannins due to the various chemical reactions that occur during winemaking and storage.”
High Tannin Wines
Courtesy of Wine Folly
Low Tannin Wines
Although scientists have never fully understood how plants produce tannins, according to Lynn Alley with Wine Spectator Magazine, an international team of scientists recently discovered tannin-producing organelles — a specialized part of a cell — in plant cells they call “tannosomes.”
Working at the French National Institute for Agricultural Research at Montpellier, the research team reported the discovery in an article in the Annals of Botany.
In search of the tannins source, scientists detected the tannosomes while examining organelles in cells from multiple species of plants. Organelles are specialized parts of cells with specific functions. Initially, they assumed they saw chloroplasts, then realized organelles were actually producing tannins.
Alley explains that scientists think the caustic and acerbic tannins act as a primary mode of protection against predators and disease in the plant kingdom.
“Nearly all vascular plants contain tannins to some degree, often concentrated in the skins and seeds. Their bitter taste serves to deter creatures from munching on the plant’s vulnerable parts. Imagine the mouth feel and taste of an underripe persimmon or the bitter red skin around a peanut.”
Because tannins are water soluble, tannins from the stems, skins, and seeds of grapes and the tannins found in oak barrels make their way into the wine. And it’s the chemical reactions of tannins in the bottle that affect how a wine ages.
Alley notes the discovery of tannosomes will spawn new ideas in wine making.
“The manner in which tannin pre-cursors are assembled leads to different qualities in grape tannins and finished wines,” said Matt Brain, lecturer and cellar master at California Polytechnic State University’s newly formed department of viticulture and enology.
“Winemakers and growers might better understand how to more precisely impact tannin quality”