After bottling, still wines begin the reductive stage of maturation without or with very little oxygen. Many producers store mainly higher quality, mature red wines, but also white wines before marketing up to 12 months or even longer in the bottle, which is why they are also called bottle ageing or bottle refinement. In many countries a certain bottle maturity is also prescribed by wine law for individual wines. In contrast to aging, by which one understands all changes of a wine until the "end of its life", bottle aging rather only summarizes the positive changes until the climax. However, there is no clear distinction between the two terms. In connection with the climax of a wine, the term "drinking maturity" is often used, meaning the optimal time for enjoyment. This state can be given, so to speak, even before the climax. However, the two terms can also be understood as synonymous, as they are by no means to be understood in relation to a specific date and can extend over a longer period of time, i.e. also over several years.
Barrel ageing has a positive effect on the maturing process. For long-lasting wines, bottle ageing is a process until, in extreme cases, they reach their peak only after many years (rarely decades) and then decline again. During the complex ageing/maturing process, the appearance and aroma change. The chemical changes are partly caused by oxidative processes with also conscious oxygen management. Depending on the type of closure, a supply of oxygen known as micro-oxigenation (nanooxigenation) also occurs in minimal quantities through the closure. This can even be consciously controlled by means of special closures (e.g. Nomacorc, VinPerfect). However, many processes during are not dependent on oxygen, but on reactions between the other ingredients or their decomposition. The biochemical processes controlled by enzymes consume the oxygen, but would also take place without it, but much more slowly. The interaction of oxygen, acids and alcohol leads to the enrichment with ester. These are taste-intensive, mostly volatile compounds with a sweet-fruity aroma. The amount of acids does not change, although this subjective impression is created by older wines. They even become more prominent again at the "end of life".
The colour goes through a typical cycle of change, which also allows conclusions to be drawn about age. In red wines, the anthocyanins (colouring agents) change from initially dark purple or bluish red first to lighter colours such as ruby red, garnet red and brick red and then to darker, brownish red tones. At the end of its life, a red wine that no longer tastes optimal then shows a completely brown colour. In this process, phenols are polymerised to form a crust (baked together). These substances are deposited as a deposit at the bottom of the bottle. However, they are by no means to be regarded as wine faults and can be removed by decanting as carefully as possible. White wine contains much less tannins, so the change is not as great. The initially straw-yellow to light golden colour with often greenish reflections changes continuously to darker tones. With certain grape varieties with a high phenol content, the colour can change up to deep yellow and orange-yellow. If browning occurs, this is usually undesirable. At the end of its life, a white wine also turns dark brown. The grape variety and the method of vinification also have an influence on the colour. Wines with oxidative ageing, such as sherry, port or from botrytised berries, always have a deeper, darker colour.
Tertiary aromas develop during bottle aging and the complex chemical processes that take place during this process. Their formation begins with the decomposition of the carbonic acid dissolved in the young wine, the polymerisation of substances and the esterification. Everything that was "hard and angular" in the wine now becomes "rounder, gentler and more harmonious". An important aspect is the "right age for enjoyment" of a wine. Some wines must be stored in the bottle for several years before they can be marketed according to the legal regulations of the respective countries. However, the process of developing a wine also comes to an end, because no wine can be kept indefinitely and does not become "eternally better". The cork or closure also plays an important role. If it becomes brittle and permeable to air, oxidation can begin through the entry of oxygen.
A frequently asked question is whether substances - and if so, which ones - are degraded over time. According to analytical measurements, there is no measurable decrease in residual sugar as a result of natural ageing, or at most a marginal decrease (perhaps 0.5 g/l). The same applies to acids and the pH value. The apparent reduction of sweetness (sugar) in matured wines is an "imaginary" sensory sensation. Essentially, this impression is due to the fact that other substances in the wine, such as tannins, as well as vegetal and mineral tones, are more palatable, while the fruity notes are much less present. Young sweet wines in their primary fruit phase also taste sweet because the youthful fruit further enhances the sweet impression. For this purely subjective taste sensation, see also under the keyword sugar content.
In the further development phase of the wine, these primary fruit aromas slowly disappear over time, while now bitter tasting components become more prominent. The impression of sweetness can thus subjectively become noticeably less, although the actual sugar content has not changed at all. For nominally dry wines with a few grams of residual sugar, the exact opposite effect can even occur. In the primary fruit phase, the existing sweetness is partly equated with fruit and therefore not perceived separately from it. If the primary fruit disappears, the sugar remains clearly visible and is suddenly perceived separately, which makes the wine appear sweeter.
Oxidative processes can cause the development of ageing aromas such as aging tones and firn. These are usually understood as wine faults. However, firn is accepted as a positive in small amounts and for certain wines. If the cork is damaged, a new corking is therefore worth considering what some wineries offer as a service for their best products. A further development in the bottle up to a climax usually only occurs with still wine. With a sparkling wine (see there) the development is in most cases completed from the time of marketing or the peak has already been reached. The same applies to distillates of all kinds, such as Armagnac, Cognac, brandy etc. All the (positive) changes during the maturing process can of course not yet be present in a young wine that is to be enjoyed quickly. See also the keywords durability and vintage, as well as oldest wines and most expensive wines.