In grapes, tannins are one of the most important families of compounds that eventually impart a wine’s mouthfeel.
Obviously, tannin composition is a key point, and winemaking processes strongly contribute to the final tannin’s composition, with reactions of addition, oxidation, polymerisation, and aggregation involving the native forms. However, the grape variety can influence the profile of the different phenolic families and, thus, the final composition of tannins in the wine and the sensory properties they induce. Note that the higher the degree of polymerisation and galloylation of tannins, the more astringent they are.
The quantity of tannins, on the other hand, is more dependent on the maturation conditions.
These evolutionary mechanisms can lead to the preservation/formation of polyphenolic structures that present a high interaction with proteins, especially Proline Rich Proteins (PRPs), inducing the partial precipitation of protein-tannin structures. This reaction partly explains the decrease of wine astringency when protein fining reagents are used.
Similarly, grape polysaccharides that are extracted mainly during maceration and pressing indirectly contribute to the mouthfeel of wine. If grape polysaccharides are not abundant enough to be directly perceived in the mouth, they can prevent tannin aggregation or reduce their size.
These aggregates are known to be more astringent, and thus the presence of polysaccharides can reduce astringency.
Among the huge diversity of grape polysaccharides, rhamnogalacturonan II is the only compound that seems to have a direct and specific contribution to a decrease in astringency, avoiding the precipitation of tannin-protein structures in the mouth.
Polysaccharides and rhamnogalacturonan II clearly decrease wine astringency, as recently reported in statistical studies that combined polysaccharide composition and sensory.
On the contrary, the impact of oligosaccharides resulting from pectinase addition is not so clear, with controversial data highlighting the importance of the size and composition of mannose and galactose in those compounds.
Tannins can be directly absorbed by the yeast cell wall during alcoholic fermentation, thereby decreasing their level in wine and, correlatively, their higher presence in lees after alcoholic fermentation. This mechanism could partly explain the roundness of wine fermented with Fermivin XL in comparison to other strains.
Even if autolysis is a natural phenomenon occurring after alcoholic fermentation, it can be accelerated using β-glucanase enzymes. These enzymes can degrade the yeast cell wall since they are able to hydrolyse β-glucans that are constitutive of the cell wall. The effect of glucanase addition such as Rapidase Batonnage on mannoprotein release can be observed. The release of mannoproteins during lees ageing contributes to decreased wine astringency, increased unctuosity and mouthfeel, but also to tartaric, protein and colloidal stabilisation.
Another way to take advantage of mannoproteins in wine is the addition of mannoproteins extracted from yeast and proposed as ready-to-use products, such as Claristar and Final touch which contribute to tartaric stabilisation and present a strong organoleptic impact. A full range of products are available with different applications depending on the yeast strain and extraction process used. A good example of the impact of such a mannoprotein is illustrated by the effect of Final touch GUSTO addition on tannin perception.
With a highly qualified team of experts in many fields, Oenobrands strives to offer winemakers’ novel and scientifically sound solutions, as well as to highlight the positive synergies between its products.
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