Phenols in wine
The phenols in wine comprise a group of several hundred chemical substances from the group of polyphenols . The phenols essentially influence the color , smell , taste and texture of the wine . You are responsible for the difference between white and red wine . In addition to the visual and gustatory properties, the reactive group has antibacterial and antioxidant effects, has an influence on the vitamin content of the wine and seems to have a positive effect on the course of cardiovascular diseases. In this context they are held responsible for the phenomenon of the French Paradox . The predominant part of the phenols belongs to the family of secondary metabolites of the vine, i. that is, they appear to be expendable for the survival of the plant. The water-soluble phenols are usually stored in the vacuoles of the berry in the form of glycosides .
Some of the phenols (mostly non-flavonoid substances) are contained in the juice and pulp of grapes . The winemaker has only little influence on their share in the wine and essentially represents the characteristics of the grape variety . The flavonoids are concentrated in the berry skin, the pips and the stems or the stalk . The amount of extracted components in the wine can be controlled by means of winemaking techniques such as the standing time of the mash fermentation , the proportion of stems in the mash, etc. Too high a proportion of flavonoids in white wine or sparkling wine is undesirable. During winemaking and later aging , the chemical structure of many of the phenols in wine changes. Little is known about the change mechanisms.
Different phenols can be introduced into the wine by choosing the fermentation and aging container. The new oak wood of the barrique can bsw. Depending on the origin and degree of roasting, add a shade of vanilla in the form of vanillin .
Gustatory perception
At present, at least five basic qualities of gustatory perception are assumed:
- sweet - triggered by sugar , also by some amino acids , peptides , alcohols , see also: sweeteners
- salty - triggered by table salt , also by some other mineral salts
- acidic - triggered by acidic solutions and organic acids
- bitter - triggered by a variety of different substances, see also: bitter substances
- umami ( Japanese : meaty, hearty) - triggered by glutamic acid and aspartic acid .
It has been known since the beginning of the 20th century that the different taste qualities are perceived by all taste-sensitive parts of the tongue . The differences between the tongue areas with regard to the sensitivity for individual qualities are only slight in humans. Nevertheless, in many textbooks, the tongue is still divided into “taste zones”.
The taste-forming phenols are mainly assigned to the group of bitter substances .
The substances
Flavonoids
The flavonoids are a group of water-soluble plant dyes and play an important role in the metabolism of many plants . According to the DGE, there are over 6500 different flavonoids. Most flavonoids are bound to glucose or rhamnose - hence they are called glycosides. Only the flavanols and the proanthocyanidins are not bound to sugar molecules (= aglycones ).
Flavones
Flavones are yellow plant dyes . About 300 naturally occurring flavones are known. Like other flavonoids, they occur as water-soluble glycosides, e.g. B. hyperoside and quercitrin , hesperidin , luteolin or chrysin . The resulting color in white wine ranges from pale yellow-green to rich golden yellow. The first-mentioned color is mostly characteristic of white wines from northern wine-growing regions. The pale yellow-green is typical for a Chablis or a Riesling from the Moselle wine-growing region .
The very common straw yellow ranks between the yellow-green and the golden yellow. The golden yellow usually indicates a high-quality sweet wine such as a Beerenauslese or Trockenbeerenauslese or the Bordeaux family from Sauternes and Barsac . White wines - in contrast to red wines - gain in color intensity with increasing bottle maturity.
Anthocyanins
Anthocyanins (from the Greek anthos = blossom, flower, kyáneos = dark blue) are water-soluble plant pigments that occur in almost all higher plants and give the flowers , fruits and some leaves a red, purple, blue or bluish-black color. In the grapes, the anthocyanins develop at the beginning of ripening (stage 81 on the BBCH scale for grapevines ). At this stage, the color of the grape skin of red grape varieties changes from green to red to blue-black. In most cases, the vegetable pigments are found exclusively in the berry skin, while the juice and pulp of the berry are colorless. This also explains that white wines can also be made from these red grape varieties (→ Blanc de Noirs ). This practice is particularly common in Champagne , where the Spätburgunder (Pinot Noir) and the Müllerrebe (Pinot Meunier) are used in large numbers to produce white sparkling wines. In order to win a red wine, the dye must be released from the berry peel. This happens during the maceration and maceration, where the fermenting or already fermented juice remains in contact with the berry skins.
The proportion of tannins and anthocyanins can vary by 100% depending on the year , the acidity by 50% and the must weight by up to 15–20%. One of the tasks of anthocyanins in plants is to protect the plants from the strong UV light of the sun by absorbing certain wavelengths. This prevents damage to the proteins in the cell and the DNA in the cell nuclei . The amount of dyes formed also depends on the intensity of the radiation. That is why you can almost only find white grape varieties in northern growing areas. Red berries that did not reach full phenolic ripeness result in wines with a grassy character.
Ampelographers find an abundance of anthocyanins in the grapes, which are responsible for the whole range of color variations. The most important are cyanidin , peonidin , petunidin , delphinidin and malvidin . The composition of the dyes depends on the grape variety. The ampelographs make use of this fact to identify individual varieties. In the middle of the 20th century, they also used a specialty of the noble grapevine Vitis vinifera to check whether the ban on the so-called hybrid or American grape was observed. While the anthocyanins from Vitis vinifera are almost exclusively bound to one sugar molecule, in the grape varieties derived from Vitis riparia and Vitis rupestris they are bound to two sugar molecules.
Red wines come in very different hues, which change from a strong violet-red through all red tones (purple, ruby red, garnet red) to red-brown or amber tones after aging.
Whether an anthocyanin is more red or blue depends on the pH of the wine. A wine with a low pH value (i.e. a strong acidity) favors the red appearance; at high pH values, shades of blue predominate. When the bottle is stored, the anthocyanins in the wine react with acids and tannins. The products fail together and can form a bottle depot. The color of the wine then tends to be reddish brown, which ideally is a sign of longer aging in the bottle. Red wines lose their color intensity with age.
Tannins
The group of tannins influences the color of the wine, the storage time required to be ready to drink and the texture of the wine. The content of tannins ( gallotannins and ellagitannins ) and their structure are a decisive factor for the quality of a wine . It is sometimes mistakenly assumed that red wines have a longer or shorter shelf life depending on the tannin content. Tannin prevents the oxidation of the wine, but nowadays this can also be achieved by adding potassium disulfite (potassium pyrosulfite). It gives the wine a characteristically rough note of dryness, the so-called astringency . The bitterness comes from a reaction between the tannins and some proteins in the saliva . The ability to react with proteins also largely determines which food goes with which wine. Today oenology knows more than 30 different tannins. Some are important for the quality of the wine, others are classified as unfavorable. In principle, tannins play a greater role in red wines than in white wines, since tannins are always extracted from the berry skins with the coloring agents. These natural tannins cannot be hydrolyzed and are formed by enzymes during the metabolism of the berry. The grape varieties Cabernet Sauvignon , Nebbiolo , Syrah and Tannat have a very high proportion of natural tannins.
Tannin is also transferred from oak barrels to wine ( barrique ) if these have not been made wine green . However, the supply of oxygen also promotes the polymerisation with anthocyanins , so that the tannin content of the wine is usually lower after the barrel aging than before. The tannins from the barrel aging are hydrolyzable (e.g. gallotannins as a product of gallic acid , ellag tannins as a product of ellagic acid ).
The tannin content of a wine decides less about its shelf life than about how long it needs to be stored: As the bottle matures, the tannins polymerize with anthocyanins to form long-chain molecules that do not have astringent effect. The astringency of the wine is steadily decreasing, which makes the wine more pleasant to drink. The prerequisite for this is the presence of a sufficient concentration of anthocyanins (dyes). With the technique of micro-oxygenation one tries to reduce the need for storage.
Late grape harvest and high physiological ripeness ensure that tannins are ripe and perceived as soft. Immature tannins, on the other hand, taste green, aggressive and furry.
Catechins
The grapes of the noble grapevine ( Vitis vinifera ) are rich in (+) - catechins , (-) - epicatechins, (+) - gallocatechins, (-) - epigallocatechins, as well as the esterified form, the epicatechine-3-O-gallate. These flavanols from the Flavan-3-ole group have a bitter and astringent taste and are only found in the kernels of the berries. The content of catechins varies depending on the grape variety, terroir , vintage and phenolic ripeness of the berries. The Merlot and Cabernet Sauvignon grape varieties have extremely high quantities of flavanols.
| Flavanol content in the kernels of grape varieties (harvested in Tuscany, Italy). Content in mg / kg MS |
||
|---|---|---|
| Grape variety | (+) - catechins | (-) - epicatechins |
| Merlot | 1388 | 1318 |
| Cabernet Sauvignon | 1418 | 1276 |
During winemaking, the winemaker can influence the extraction content of the phenols from the peel and seeds of the berries using various parameters of the mash fermentation. The amounts of catechins in red wine fluctuate as follows.
| Average content of flavonol in red wines results in mg / l |
|||
|---|---|---|---|
| Flavanols | maximum | minimum | Average |
| (+) - catechins | 300 | 20th | 130 |
| (-) - epicatechins | 120 | 5 | 60 |
| (+) - Gallocatechins | 80 | 7th | 35 |
| (-) - epigallocatechins | 35 | 2 | 13 |
On average, there are 238 mg / L flavonols in red wine. This corresponds to an amount of 28.5 mg in a 12 cl wine glass .
Phenolic acids
Phenolic acids (phenol carboxylic acids) are aromatic chemical compounds that belong to the group of hydroxybenzoic acids or hydroxycinnamic acids. The berries and the wine contain benzoic acids and cinnamic acid . In red wine the concentration is 100–200 mg / l, in white wine it is only 10–20 mg / l. Of the seven known benzoic acids, only traces of salicylic acid and gentisic acid occur. In the must, the cinnamic acids and tartaric acid are esterified . Both acid families are perceived as colorless and odorless, but represent the precursors of volatile phenols.
literature
- Jancis Robinson : The Oxford Wine Lexicon . 1st edition. Gräfe and Unzer Verlag, Munich 2003, ISBN 3-7742-0914-6 .
- Michael Broadbent : Check out wines, know them, enjoy them . 3. Edition. Raeber Verlag, Lucerne and Stuttgart 1986, ISBN 3-7239-0040-2 .
- Pascal Ribéreau-Gayon , Denis Dubourdieu, Bernard Donèche, Aline Lonvaud: Traité d'oenologie, Microbiologie du vin. Vinifications . 5th edition. Dunod, Éditions La Vigne, 2004, ISBN 2-10-007301-X .
- Pascal Ribéreau-Gayon, Denis Dubourdieu, Yves Glories, Alain Maujean: Traité d'oenologie, Chimie du vin. Stabilization et traitements . 5th edition. Dunod, Éditions La Vigne, 2004, ISBN 2-10-007302-8 .
- Claude Flanzy (editor and coordinator): Oenology, Fondements scientifiques et technologiques . 1st edition. Lavoisier, Éditions Technique & Documentation, 1998, ISBN 2-7430-0243-3 .
Web links
- R. Eder, S. Wendelin: Phenolic composition and antioxidant capacity of grapes and wines . (PDF) Section Wine and Fruit, Klosterneuburg
Individual evidence
- ↑ Carole Viriot, Augustin Scalbert, Catherine Lapierre, Michel Moutounet: Ellagitannins and lignins in aging of spirits in oak barrels . In: Journal of Agricultural and Food Chemistry , 1993, 41 (11), pp. 1872-1879, doi: 10.1021 / jf00035a013 .
- ^ B. Lindemann: Receptors and transduction in taste . In: Nature . No. 413, 2001, pp. 219-225, PMID 11557991 .
- ↑ P. Iacopini, M. Baldi, P. Storchi, L. Sebastiani: Catechin, epicatechin, quercetin, rutin and resveratrol in red grape: Content, in vitro antioxidant activity and interactions . In: Journal of Food Composition and Analysis , Vol. 21, pp. 589-598, doi: 10.1016 / j.jfca.2008.03.011 .
- ↑ Nicolas Vivas: Les composés phénoliques et l'élaboration des vins rouges . 2007, Editions Féret.
- ↑ Entry on phenol carboxylic acids. In: Römpp Online . Georg Thieme Verlag, accessed on June 16, 2014.