life in a wine >

2010
life in a wine

Science likes to offer simple answers, nature rarely poses simple questions. A science of making top quality wine does not exist – instead we have a collection of scientific understandings of narrow questions relating to the making of fine wines and it is up to the winemakers to assemble the knowledge required for their own situation/terroir. It is not surprising then that winemakers do not (or should not) slavishly follow “recipes” from elsewhere. Nevertheless, for fine wine, there is one common goal which all will strive for and that is the need for a long-lived wine to allow the development of the virtues and flavours of the classic varietal(s) in the bottle.

Understanding what constitutes potential for long life in a wine is best approached by discussing its death. This is signaled by the wine flavours becoming obviously oxidised with loss of and/or browning of the colour, sherry-like (aldehydic) flavours and aromas, plus diminished fruit flavours. Slow oxidation does play an important part in the maturation process – we just need to slow it to an acceptable level else our beautiful, maturing wine will have the transient life of a butterfly. A long-lived wine therefore, is one with the constitution to resist just these processes and those parts of its makeup which equip it to do so are all those sacrificial constituents which are able to be oxidised from a reduced to an oxidised form. Too little of these constituents will result in a wine which does not have the life expectancy for it to realize its potential, too much will make the wine taste overly structured and the desirable flavours will fade before this structure allows the wine to be drunk with pleasure.

Coupled with the need for sufficient antioxidants to protect wine from too rapid an oxidation is the need to control the processes driving it. The juice from healthy grapes free from physical damage contain the enzyme grape polyphenoloxidase which is relatively slow in action and whose activity diminishes through the winemaking process till the slow nonenzymatic autooxidation reactions are all that finally remain viable in the bottle. However under vintage conditions promoting mould and botrytis, fungal polyphenoloxidases (laccase) are introduced. These are much more resilient to the winemaking processes, and are much more effective and rapid in oxidizing juice and wine even in the presence of our protective antioxidants. Unfortunately even healthy grapes exposed to these adverse vintage conditions experience raised laccase levels so that while meticulous vineyard management can greatly reduce its pres- ence it will not be eliminated. Thus one may note that while our own ’02 and ’04 vintages have matured faster than usual (albeit still as interesting and attractive wines), if the vineyard management was not so painstaking and the harvest not free of mould, the wines may well have expired already. It is worth noting that enzymatic reactions can be very temperature sensitive – at least 12ËšC seems critical for their activity – so cellaring at or preferably a little less than this is desirable.

Starting with the most delicate white wines; apart from prior meticulous vineyard management, an important and traditional line of defense is that of sulphur dioxide added by the winemaker and which is occasionally augmented by vitamin C (which also occurs naturally in the juice). However in the absence of other reinforcements this protection is likely to run out relatively quickly and for a longer lived wine other natural attributes are called upon. Some commentators invoke the “acidity” of red wines as being helpful but they commonly confuse the flavour of tartaric acid and certain phenolics so it should be emphasised that the concentration of tartaric acid has no direct bearing on how a wine ages. In scientific terms a low “pH” does have an important influence but there is no direct correlation between pH’s of different wines and their acidities. Low pH enhances the protective effect of sulphites as well as slowing the progress of the deleterious oxidation reactions. (Incidentally it also changes one’s perception of flavours, bestowing a “brightness” on them as well as conferring a leaner more elegant palate.) At its lower values pH is therefore capable of making a significant contribution to longevity, particularly in the range 2.7–3.0 as encountered in fine Rieslings. Too much alcohol is also often quoted as limiting the longevity of a wine: I remain unconvinced on this and feel that a more likely explanation derives from the correlation between rising sugars and diminishing levels of grape phenolics near harvest.

In red wines it is certainly clear that phenolics or what are perceived as the “structure” of a wine are by far the most important contributor to longevity. Phenolics are also present in white wines but at the lower levels at which they are found there, they are less of a factor than for reds. In whites other anti-oxidants are necessary for augmenting stability towards oxidation in the bottle. A group of natural peptides including glutathione and cysteine have recently been proposed as having an important role in the ageing of white wine, as well as the inevitable sulphur dioxide – the latter tying up any aldehydes as well as acting as antioxidant with or without the presence of Vitamin C. Viticultural factors and choices can influence the amounts of all naturally occurring compounds in the grape and thus high crop levels, inappropriately warm vintages for a given varietal and shaded crops all matter and must be considered as factors by the viticulturalist if he/she is aiming for wines with good concentration and ageability.

Even if the viticulturalist does the job well we have no guarantee the final wine will have retained enough of the original store of antioxidants after winemaking to sustain it through an adequate period of maturation in the bottle. It is important for the winemaker to retain adequate levels of these natural constituents (of the right quality) during processing just as you and I strive to retain enough of our savings in the bank. Different parts of the winemaking process may inadvertently or otherwise expose wine to air and reduce this “bank” of antioxidants . The most significant of these possibilities occur post-fermentation and include transfers between tanks and barrels, during tank and barrel storage, and around the bottling process. For the more delicate whites, protection even starts right back where the grapes are first pressed to yield juice.

It would seem that taking steps to protect the product during its making is nothing more than an exercise involving care, attention to detail and inert gases. However the more carefully one protects the product the more phenolics are preserved: both good and bad facets of the wine structure become more obvious and are preserved in the final product. Winemakers either choose to allow some contact with air in an effort to moderate the unwanted phenolic contributions or they have to learn to enhance the way the wine is processed (mostly in how the crushing, pressing and plunging the reds is done) so that the presence of the unwanted phenolics is minimized. There are winegrowing regions of the world where production of phenolics in the grapes is over-abundant and a tendency to favour oxidative solutions to this during processing is very common and easily rationalised. Nevertheless oxidative management is a rather indiscriminate tool and one wonders what delicate flavour components may also be sacrificed at the same time.

There has been much debate about closures, corks versus screw caps and this is where I make the point that slow, discriminating oxidation such as found in barrels and through corks closures can be a very positive thing … depending. In choosing between the two types of closures there can be no definitive answer as to which is “best”, it is yet another winemaking choice with oxidative consequences for the final product. In a nutshell the effective difference between corks and the present generation of screwcaps is that the former allows tiny amounts of oxygen to progress through it into the wine and the latter provides a perfect seal. The choice impacts on how well the bank of antioxidants in the wine is preserved during cellaring and if the wine is constituted according to the conventional conception of fine wine – i.e. with an high redox potential (i.e. strong defences against oxidation) – under the screwcap the structure of the palate would not be expected to soften and the wine will not mature according to traditional expectations. On the other hand if the structure is already light and the wine very approachable, halting the progress of oxidative maturation of the wine could be critical to its survival over an acceptable period and preserving the flavours close to what they were at bottling would presumably also be acceptable.

The anti-oxidative (redox) potential of wines is not always evident from tasting – particularly with respect to whites and this is presumably because not all their reductive potential is associated with phenolics. Thus the best choice of closure for a given wine is not always self-evident. If the wine antioxidants are starved of oxygen the “redox” equilibrium in the system will assume a different point of balance and the anti-oxidants are now able to attack other naturally occurring sulphur containing compounds in the wine, transforming them to products which may have unattractive smells or others which repress one’s ability to smell much of the fragrance already there. Furthermore the palate will start to taste more structured – leaner and harder – than it did even at bottling. A prerequisite for reaching appropriate wine maturity therefore has to be that the total oxidation available to a wine has to be sufficient to moderate the structure of the wine to a point where it is aesthetically acceptable. There is no doubt that slowness of oxidation mediated by barrel or cork is the safest and most gentle way of reaching this endpoint. Since bottle maturation of fine wine is by far the longest part of the process, if the endpoint of the oxidation is reached such thatmaturation under cork is not necessary, it would not be surprising that the results under screwcap appear qualitatively different. If the desirable endpoint of oxidation is not reached and the wine then resides in a bottle under screwcap there can be unexpected consequences.

“...high crop levels, inappropriately warm vintages and shaded crops all matter and must be considered...”

Our Musings