understing botrytis and dessert wine styles
Botrytis and dessert wines are sweet wines in which high levels of sweetness have been offset against a greater concentration of flavour so that their primary impact should remain with flavour rather than just sweetness, which can otherwise become simple and cloying. Concentration of flavour from the grapes is achieved by natural shrivelling on the vine; by shrivelling owing to the botrytis fungus on the grape skin; or by the grapes freezing on the vine and, while still frozen, having concentrated juice pressed from them (for the production of 'eiswein'), leaving the extra water in the form of ice in the grape press. Lesser sweet wines can also be made artificially by freeze-concentrating juice, by reverse osmosis and other techniques. We will confine our comments to wines from traditional, natural processes.
The styles in which the sweet wines are made vary, but closer examination reveals a pattern dictated in the first instance by the varietal used. High alcohol, high acidity and high phenolics have the potential to clash by reinforcing the perception of each other (synergism). Thus, a high acid variety such as Riesling, would not normally be fermented to high alcohol - 12% is the likely limit (and most German Rieslings are much lower than this). On the other hand, low acid varieties such as Pinot gris and Gewurztraminer (in Alsace) and Semillon (in Sauternes) are frequently fermented to 14% and higher, and this extra alcohol gives the wine the structure which may be needed in the absence of a good acid backbone or adequate underpinning with wood. High alcohol wine will also taste less sweet at a given concentration of flavour, and this is an added benefit when it is required to accompany food such as Alsace cuisine: it tends to be perceived as 'rich' rather than 'sweet'.
The particular virtues of each varietal must also be considered, paramount is Riesling, whose reputation rests almost solely on its exquisite varietal character and poise when ready for drinking. This variety is epitomised by the great late-harvest wines from Mosel (and other areas), notable for their purity of expression, unobstructed by overt botrytis notes or other 'add-ons' such as barrel flavour. This is not to say that (for example) botrytis cannot subtly modify the flavours found in the wine, but it would be my expectation that such changes would arise from botrytis metabolism of flavours, such as peaches of unaffected wine being seen as apricot in the dessert version. These are changes which do not obscure the essential varietal flavours and nature of the wine. The differences need not be blatantly obvious in the young wines, but can become more evident later as the fruit (and modified fruit) continues to emerge. I also place honeyed characters in this category. Gewurztraminer and Pinot gris are two other varieties which are interesting for their varietal characters and are most frequently found as dessert wines, in Alsace. It is worth noting that, in my experience, comparative blind tastings of the high alcohol Pinot gris, Gewurztraminer and Sauternes styles almost invariably favour the former varietal Alsace wines when comparing wines of similar prices.
A variety such as Semillon tends to be much more neutral and have less easily defined flavours. As with dry Chardonnay table wines, winemakers tend to create 'add-ons' by fermenting partially clarified juice for more overt botrytis characters and by barrel fermenting. By such techniques, they create a wine of character, complexity and interest without which the varietal stand-alone style might seem rather ho-hum. In Sauternes it is not uncommon for winemakers also to blend in a small amount of varieties such as Sauvignon blanc and Muscadelle for further interest.
In New Zealand there is a growing interest in late-harvest Chardonnay dessert wines. Relatively interesting varietal flavours can develop in these wines given time, but they will probably not match Riesling and the more traditional varietals. Their naturally high acid levels mean that high alcohols and extensive wood treatment (as with Sauternes) have to be approached cautiously, and the use of more complex botrytis influence, subtle wood handling, and blending with other low acid varietals such as Pinot blanc and Pinot gris seem more promising directions for the evolution of this wine style.
Apart from the obvious techniques for adding complexity to the wine (discussed above), the winemaker can also influence it in more subtle ways. Leaving the juice on the skins for prolonged periods prior to fermentation may well extract more varietal and modified varietal flavours, leaving the wine more golden in colour, more powerful in character and more obviously appealing as a young wine. However, this also raises the level of skin phenolics, so that the wine will appear more coarse as it gets older, and it will probably oxidise and age faster. Unless handled with particular care, the technique is therefore more suited to earlier drinking botrytis wines. Botrytis juices have high levels of natural enzymes (laccases) which make them very sensitive toward oxidation. Extra exposure to air early in the life of the wine will also make it more golden, and will provide obvious and interesting botrytis characters in a young wine. The downside of this is that oxidation can damage the varietal and still-to-be developed varietal flavours. The net effect of this technique is possibly a more interesting young wine, but its long-term potential (as far as varietal characters) is compromised. The more complex Sauternes styles rest less on their varietal flavours, and employ techniques which can counter problems arising from extra phenolics and oxidation. There is still a balancing act in making these wines, but the overall equation is quite different.
Our approach to botrytis wines is based on their being able to reach their potential. That is, I endeavour to preserve as much as possible of the desired flavours (and those flavours which are yet to emerge) in the framework of a wine which will become harmoniously complete and remain relatively youthful when its potential is fully realised. This requires something of a balance between what can be done to make a young wine more attractive and what may detract at a later stage. Overall these wines can be very long-lived, and it need not be surprising that many botrytis-affected wines with impressive pedigrees appear quite understated in their youth.
And how do we use these wines? Chapters can be written on the subject, but I will confine myself to a few simple observations. The French serve sweet wines as an aperitif prior to dinner for the civilised purpose of taking the edge off the appetite and presumably allowing the dining to proceed in a leisurely fashion. But beware. The chosen wine must not be too sweet or concentrated, or it may dull your palate to the pleasures of the wines to follow. Matching sweet wines with food, cheeses and desserts is not simple. The low acid, high alcohol varieties and wooded wines match strong flavours most easily; the high acid, low alcohol wines are frequently but not exclusively well matched with fruit of similar acidity. In either case, a rule of thumb is that the wine should be perceptibly sweeter than the food it accompanies. An easy solution to serving these wines is to have them after a grand meal without accompaniment, but if this wine is a particular treasure it is worth determining that your friends' faculties are still fully capable of appreciating it. I frequently broach such wines outside a meal situation - on a summer's afternoon or as a restorative to remind me how wonderful life is. Whatever the circumstances, these wines should be the ultimate hedonistic expression, and their use deserves careful consideration so that they can be appreciated as such.