Polymerisation
Polymerisation in wine refers to the chemical process by which small phenolic compounds, particularly tannins and anthocyanins, bond together to form larger molecular structures. This reaction, central to the transformation of wine during ageing, influences colour stability, mouthfeel, and overall balance[1].
Definition and chemical basis
Polymerisation describes the joining of monomeric phenolic molecules into dimers, oligomers, or long-chain polymers. In wine, the most significant reactions involve the combination of tannins with anthocyanins and other flavonoids[2]. These reactions occur spontaneously but are influenced by the presence of oxygen, pH, sulphur dioxide, and storage temperature.
Role in wine ageing
The process is fundamental to the ageing of red wines. In the early stages, anthocyanins, which provide youthful wines with vibrant purple-red colour, gradually bind with tannins to form more stable pigments. This transformation explains the shift from bright hues towards the garnet and brick tones typical of mature red wines[3]. Simultaneously, tannin polymerisation reduces the astringency of young wines by precipitating or forming colloids less readily perceived as harsh on the palate.
Oak barrel maturation can accelerate polymerisation due to controlled oxygen exposure through the wood, whereas ageing in bottle proceeds more slowly. Micro-oxygenation, used in modern winemaking, seeks to mimic the controlled oxygen ingress of barrels to encourage polymer formation in a shorter timeframe[4].
Impact on sensory qualities
Polymerisation has profound consequences for wine appreciation. Large polymeric tannins are less reactive with proteins in saliva than their smaller counterparts, leading to a perceived softening of texture and reduced bitterness. The process is also associated with increased roundness and integration of structure, often described as a shift from angular to harmonious balance[5].
Colour stability is another key outcome. By forming polymeric pigments, wines retain visual depth for longer periods of ageing. The slow evolution of aroma is linked indirectly, as the oxidation and polymerisation of phenolic compounds contribute to the development of tertiary notes such as leather, spice, and dried fruit.
Factors influencing polymerisation
Several factors affect the rate and extent of polymerisation. Grape variety plays a central role: thick-skinned grapes such as Cabernet Sauvignon and Syrah supply abundant phenolic content conducive to polymer formation, whereas thin-skinned varieties like Pinot noir produce wines with lower potential for long-term polymer development[6]. Vintage conditions, including ripeness and phenolic maturity, also determine the composition of tannins and anthocyanins available for reaction.
Winemaking techniques strongly influence the process. Extended maceration increases extraction of seed and skin tannins, raising the pool of monomers for polymerisation. The choice of vessel — whether inert stainless steel, small oak barriques, or large casks — affects oxygen ingress and reaction dynamics. Finally, storage conditions, especially temperature and oxygen management, can hasten or slow the process and influence whether polymers remain in solution or precipitate as sediment.
See also
References
- ↑ Jackson, Wine Science: Principles and Applications, 5th ed., Academic Press, 2020.
- ↑ Ribéreau-Gayon, Dubourdieu, Donèche & Lonvaud, Handbook of Enology, Vol. 2: The Chemistry of Wine, Wiley, 2006.
- ↑ Robinson (ed.), The Oxford Companion to Wine, Oxford University Press, 2015.
- ↑ Jackson, Wine Science: Principles and Applications, 5th ed., Academic Press, 2020.
- ↑ Peynaud, The Taste of Wine, Wiley, 1996.
- ↑ Cheynier, Phenolic Compounds in Foods and Natural Health Products, American Chemical Society, 2005.