Term (also polymerisation or polyreaction) for the chemical reaction in which monomers (individual parts), usually unsaturated organic compounds, react under the influence of catalysts to form polymers (multiple parts). Simply put, small molecules join together to form large molecules. The polymers are thus interconnected long molecular chains of monomers. A distinction is made between homo-polymerization, in which only one type of monomer is reacted, and co-polymerization, in which different monomers react. In viticulture, polymerisation is understood to mean the "caking together" of microscopically small parts in wine, which are then precipitated (sink to the bottom).
There are reactions between acetaldehyde, anthocyanins (colorants), oxygen and tannins, but not all substances are always involved. The reaction among anthocyanins is called copigmentation. In these processes simple phenol molecules become complex tannin (tanning agents) and pigment polymers (dyes). The changes in colour, taste and shelf life have only been partially researched. The formation of the pigment polymers already begins during the mashing process. This process continues during fermentation and especially during bottle maturation. The colour change of a red wine during ageing from usually purple-red to red-brown is also caused by the conversion of anthocyanins to pigment polymers.
In vinification, this process is enhanced by the addition of oenological tannins. These are added at various times (maceration, BSA, bottling). Under certain conditions, they are able to promote the polymerisation of anthocyanins to more intensely coloured, sulphur dioxide-stable colour pigments. Pigment polymers stabilise the colour, improve the taste by weakening the astringent effect and contribute to shelf life. Finally, in old wines, individual polymers become so large that they precipitate from the solution and settle as a deposit at the bottom of the bottle.