tannis, palate structure and longevity in pinot noir
The third most abundant constituent in most wines is broadly classed as the ‘phenolics', and they occur in concentrations ranging from nearly zero to several grams per litre. These compounds make an essential contribution to many aspects of wine flavour, including bitterness, what may appear to be acidity, and tactile sensations relating to astringency. Part of this family of compounds is made up of flavonoids (including anthocyanins, the colour in red grapes) and they are the building blocks of an important subgroup of phenolics called 'tannins'. Their biggest role is in red wines, where they contribute to the palate structure and to the longevity of the wine when bottled. It should be recognised that tannins, anthocyanins and other groupings of phenolics consist of families of hundreds of differing molecules which act in similar but not identical ways. This means that we can only make generalisations not precise comment about how the individual groups of compounds may impact on our perception of wine or, for example, on how wines will be affected during the winemaking processes and in later maturation.
The effect of the higher levels of tannins in red wines is to impose what is frequently described as palate structure. That is, the tactile sensations associated with tannins in the mouth give a ‘textural form' to the totality of what is perceived. By helping balance the front, middle and back parts of the palate, the 'structure' of sensations can contribute to the balance and harmony of the flavours and bring a further dimension to the total experience of the wine in the mouth. It will probably come as a surprise to many that whites can have a phenolic structure similar to reds, but at a more moderate level and from smaller but chemically similar molecules. Quality whites which have been cropped low to achieve concentration seem particularly to show this feature. For example, it is common in good Riesling, and its presence appears to be the reason why the palate of those young wines can appear very lean: these active grape tannins seem to repress our perception of the fruit.
Among these groups of phenolics are many compounds which are known as ‘antioxidants'. Particularly powerful examples include the stilbene 'resveratrol', and the flavonoids 'quercetin' and 'epicatechin', all of which have consequential health-giving properties (activity against cancer, heart problems, Alzheimers, etc). Many other such compounds have yet to be identified. These same antioxidant properties protect the wines flavours against the oxygen which diffuses in through the cork while it is in the bottle (the commercial additive sulphur dioxide, which is added for the same reason, is used up within the first three years). High-extract wines which have higher levels of these compounds can therefore be expected to be better preserved and to last longer. As the phenolics are used up or polymerise in the ageing process, the winetasters repressed perception of fruit (owing to the presence of the phenolics) moderates; the fruit appears to 'fill out' as the structure softens; and the wine is finally considered to be ready for drinking. This situation applies to many wines, both red and white, and particularly those which have been made reductively or under reductive conditions* (e.g. in a cold Burgundian autumn when the oxidative processes are naturally slowed.) It is worth noting that phenol chemistry can also be used to explain the slowed oxidation and ageing effects found in wines with low pHs.
Modern winemaking has evolved in the direction of using new oak barrels as a tool for adding flavour and palate structure to the wines which are stored in them. This is at variance with the legal requirements in countries like Germany, and with the traditional approach in many parts of Europe such as Alsace and parts of Italy where wine may be stored in wooden containers but a contribution of flavour or texture by the wood is avoided at all costs. There are critical differences between the contributions to wine of oak tannins and the fruit tannins derived naturally from the grapes, grape seeds or the stems of whole bunches. Both types of tannin impart structure to a wine, and indeed many winetasters may not be able to distinguish between them. However, the fruit tannins in the wine were created in the grape not long before harvest; they may have been further activated during the ferment (a highly reductive process); and they have had little chance to do what phenols do well - soak up oxygen and be 'deactivated' in the process. On the other hand, the new oak barrels have been constructed from carefully prepared staves (planks) which have been air-dried for two or three years, during which time the oxygen-sensitive phenolics are used up, leaving stable tannins and phenolics. The net result is that fruit-derived tannins in a wine are one of its best protections against the arch-enemy oxygen, while tannins from the air-dried oak cannot be expected to be much help at all. Oak-derived tannins tend to linger unchanged as the wine ages and the fruit flavours fade, so that there is a danger that wine with high new-wood levels might end up tasting of little else. On the other hand, the wine whose structure is more derived from fruit tannins will have its flavours well protected from oxidative processes and will therefore remain in better condition. Because these tannins are more active, they will also be used up or be transformed more quickly and will become less dominant on the palate over a shorter period of time. Moreover, there are subtle but interesting flavours associated with the indigenous fruit tannins which contribute to the overall palate, and which are characteristic of the terroir of a particular vineyard, rather than a feature of barrels produced and manufactured on the other side of the world.
Pinot noir is unusual among red wines in that it has relatively low levels of grape tannins and it has to be processed in a way which takes this into account. Other reds such as Cabernet blends, Syrah, and so on have much higher levels of tannins in the skins, so that it may even be normal practice to aerate the young wine shortly after fermentation to moderate this structure. Even at bottling, the latter reds are normally so well endowed with fruit tannins that preservation of fruit for lengthy bottle maturation should not be a problem.
Several of the New Zealand Pinot noir regions have the potential to rank among the best in the world outside Burgundy, because of the powerful and attractive fruit statements that can be achieved from fruit produced in our maritime climate. On the other hand, the same climatic features accentuate the problems of deriving sufficient ripe fruit tannins for longevity and/or palate structure for the final wine. A winemaker can follow two differing routes in his/her pursuit of a favoured wine style. In the first, he/she will make a wine which depends more for its structure on fruit tannins (by whole-bunch ferments and various viticultural techniques affecting physiological ripeness), resulting in a wine which is longer lived and more individual when it is fully mature. Since these active fruit tannins also seem to repress our perception of fruit, expect the character of this wine to be less forthcoming when young but to appear to blossom as the tannins recede over the first few years. In the second approach, the winemaker uses higher levels of new wood rather than fruit tannins to achieve structure. Modern refinements in barrel making, enable him/her to utilise specialised flavours and promote palate structure in a wine which is likely to be more appealing when consumed young but which may lack what is needed for long-term development. Oxidative handling** of the wine during processing can also be used to enhance this style, providing a 'fatter', silkier wine, but with a further reduction in age potential. There remains a place for both wine styles, depending on the purpose and intended life of the wine which has been made.
*Reductive handling refers to processing grapes in a way which excludes air. This means that naturally-occurring phenolics which are sensitive to oxygen are not allowed to react with or get used up in the process; they remain as a defence against the unwanted effects of the slow oxidation of wine flavours in the bottle by the passage of air through the cork.
**This is the reverse of reductive handling. The wine is intentionally exposed to air and will lose some of its natural fruit phenolics (how much, depending on where in the process this is done). The loss of these phenolics will make the wine appear fatter, silkier and much more approachable. This can also be done in processing whites such as Chardonnay with similar results: a fatter, more approachable wine with a reduced life expectancy.