Home > Wine Features > Sweet Wine

Sweet Wine: Botrytis

Sweet Wines

Part 1: Introduction

Part 2: Must Weight

Part 3: Botrytis

Part 4: Late Harvest Wines

Part 5: Eiswein

Part 6: Dried Grape Wines

Part 7: Vin Doux Naturel

Nothing is known of when the eternal romance between the grape and the fungal organism known as Botrytis cinerea began. I like to imagine that the wonderful wines which result from the interaction of the two have provided one or two winemakers with private, individual revelations over the centuries, although in reality I think this is unlikely to be true. In modern times we have a tendency to think of our ancestors as more simple folk than ourselves who understood less, but in many areas - especially viticulture, which has been with us for millennia - this is rather a simplistic view in itself. It is my personal belief that as long as man has cultivated grapes, he has known of the effects - certainly bad, and quite probably good as well - that the process of rot can have on his harvest. Today, although Botrytis, or Noble Rot, or Pourriture Noble in French, is of importance in many wine regions, there are three principal players in the contest for recognition as the birthplace of Botrytis; they are Tokaji in Hungary, Sauternes in Bordeaux, and the Rheingau in Germany.

Although I think none can lay a certain and irrefutable claim to being the true birthplace, it is Tokaji that presents us with the best evidence for a long history of Botrytis. The Hungarians, like their peers in Germany, offer an almost apocryphal tale of a delayed harvest - in the case of the Hungarians, because of impending invasion by the marauding Turks in 1650 - which resulted in the disaster of rot in the vineyard. Abbott Maté Szepsi, priest in charge of production (evidence of how closely wine and religion have been entwined in centuries past) at the Zssuzsanna Lorántfly estate harvested and vinified the putrefied grapes separately, and found the result was a winner. The Hungarians quickly learnt that Noble Rot was to their advantage; within the next century the great sweet wines of Tokaji had a place in both French and Russian courts, and no doubt elsewhere too.

The Teutonic tale of Botrytis is no less enchanting, but sadly for the Germans it occurs a century after the Abbott's serendipitous discovery. Our player here is Schloss Johannisberg, an ancient Rheingau estate which originated from a Benedictine monastery built around 1100. Legend has it that in 1775, as the grapes ripened on the vines, a messenger conveying permission to begin harvesting, granted by the distant Prince Abbott, failed to reach the estate. The harvest was delayed, and the grapes were riddled with Botrytis; but as the Hungarians found, the results were superb. "I have never tasted a wine like it before", wrote the estate manager the following year. The relationship between Botrytis and German wine had begun, and as harvesting botrytised grapes became a desirable event, the development of Auslese, Beerenauslese and Trockenbeerenauslese categories followed.

Sauternes, probably the best known region dependent upon Botrytis, and with the largest market share of any such region - outside of the German wine auctions, anyway - was surprisingly tardy in its development. And if there is a seed of doubt in your mind regarding the Hungarian and German stories, that seed will grow into a tree with the French one. None other than Chateau d'Yquem claims to be the discoverer of Botrytis, in France at least, with the date firmly tagged to 1847. Only by overlooking the irrefutable fact that tastings of pre-1847 Yquem suggest a role for Botrytis in these vintages does this unlikely claim hold water. Yquem dates back to the 12th Century at least, with good documentation of vineyards in the 18th Century; I doubt that 1847 was the first time there was a touch of rot on the grapes.

The three principal regions for Noble Rot are joined by many others where the fungus plays a beneficial role; Coteaux du Layon and Vouvray in the Loire for instance, Alsace, Austria and even in Burgundy there are producers turning out Nobly Rotten wine. But what determines whether or not these regions are ideal for the proliferation of Botrytis cinerea is the mesoclimate, humidity in particular, and also the grape varieties. Some grapes are much more susceptible to Noble Rot than others, with close-bunched white varieties being the most suitable (red botrytised grapes lose pigment and smell off). Damp, misty mornings foster development of the mould, which settles on the grapes. If these conditions persist, however, the grapes soon moulder into a mushy grey rot; what is required is a warm, baking afternoon sun, to clear the vineyards of mist and to dry and protect the grapes. For this reason vineyards for the production of botrytised wine are often peppered around rivers and lakes (although in truth many great wine regions follow the course of a river). The vineyards of Sauternes, a small enclave in the Graves region, cluster around the Ciron and Garonne, for example; Semillon and Sauvignon Blanc are cultivated here. Tokaji has the Bodrog, and the main grape variety is Furmint, whereas the majestic Loire, assisted by its tributaries the Layon and the Aubance, sets the scene for the production of great, long-lived wines based on Chenin Blanc.

That's enough history and geography for now; many readers will already be familiar with what's been discussed so far. It's time to delve a little deeper into the world of our favourite fungus.

Botrytis Cinerea

Botrytis cinerea is the asexual, spore-forming form of Botryotinia fuckeliana (you can't make this stuff up). Don't be fooled by the different latin binomials; despite having two names, this is the same organism. In its asexual anamorphic form, the organism blights not only grapes, but other fruit crops, causing strawberry grey rot and blossom-end rot in apples to name just two; it may also damage young shoots and flower buds. On grapes it causes Botrytis Bunch Rot, which is regarded as a disaster by most vignerons who are on the whole producing dry table wines and have no desire for any rot at all. And if damp conditions persist, it leads to a rapid and globally destructive process resulting in loss of the whole crop. It is only in the conditions described above, where the grapes dry out each day thanks to the warm Autumn sun, that its effects can be so wholly beneficial.

The life cycle of Botrytis cinerea is not complex. The organism may over-winter as mycelia (the vegetative mass of fungus, consisting of branching threads of fungal cells) which lives on decaying plant matter. It may also form sclerotia, a hard, compact mass of mycelia which detaches from the fungus and which will germinate when winter has passed and growth begins afresh. With new growth the fungus produces conidiophores, branching tree-like structures bearing conidia, or spores. Mature conidia detach and are carried on the air or by rain-splash, and in the right conditions they will find and attack a new host. In many cases the conidia enter the host through already damaged or susceptible tissue; via a wound is common, although tip-scorched or withering leaves are susceptible, as are fragile seedlings. Having landed the spore generates fresh mycelia which invades the tissue, causing collapse and disintegration of the cells; the tissue softens and rots as a result - this is grey rot. With further growth the mould goes on to produce the tree-like conidiophores again, which stand proud of the host, and fresh spores are released. The process continues until the cold weather forces the organism into hibernation once again.

Where Noble Rot is concerned, however, the fungus proceeds in a subtly different manner. Firstly, the fungus affects not damaged fruit, but healthy bunches of grapes. This is especially possible as the grapes proceed to full maturity. At this stage the grapes are large and the bunches are often tightly packed; this allows for progression of the Botrytis across the bunch, possibly resulting from just a single spore landing on one of the grapes. In addition the grapes are sugar-rich, providing a food source for the fungus. Secondly, the alternation between damp misty mornings and drier, warm afternoons inhibits the rampant progression to grey rot. This is presumably because the drying out of the berries in the afternoon affects the phyopathogenicity of the organism. As a consequence, the berries dehydrate and shrivel under the influence of the Botrytis, rather than liquefying to a grey goo. This effect is consequent upon the puncture of the grape skin by the Botrytis mycelia, which permits water to escape from the berries, concentrating the sugars within. Although not grey and mushy, the grapes are still grossly unappealing to the eye, having progressed from a healthy golden hue to become a mass of brown, shrivelled berries, peppered with fungal growth. It must have taken an enormous leap of faith for those German, Hungarian and French winemakers to ferment such a harvest.

Reaping the Benefits

All great wine begins in the vineyard, and botrytised wines are no exception. One essential process when producing a great botrytised wine is to harvest selectively. Unfortunately, the march of Botrytis across a ripened bunch is not always a steady one, and some grapes will be fully botrytised, and ready for harvest, whilst others in the same bunch will be unaffected. And some bunches will be far ahead of other bunches. Hence the dedicated winemaker will have his crop harvested in a number of passes (tris) through the vineyard. With each tri the pickers will pluck only suitable affected bunches, with the first pass generally regarded as the one yielding the highest quality of botrytised grapes, hence the Harvest at Yquem premium asked for great Premier Tri Vouvray. Labour is a major factor in the high cost of producing high quality botrytised wine, and pickers require some degree of knowledge. Early Botrytis infection, which turns the grapes a purple-green, is known as pourri plein, and at this stage Botrytis cinerea consumes grape sugar without concentration of juice; hence the grapes may actually be less sugar-rich than before Botrytis set in. Pickers must wait until the grapes are fully desiccated, when they are known as confit or rôti, before harvesting. At this stage the Botrytis has consumed more sugar, but such is the effect of dehydration that the juice is highly concentrated and sweet; in addition, the fungal action creates glycerol, dextrin and other compounds which contribute to the texture and unique and desirable honey, toast and apricot flavour profile of a botrytised wine.

Also contributing to the overheads in the vineyard are low yields; shrivelled grapes do not produce as much volume of wine as healthy grapes. The maximum legally permissible yield in Sauternes may be as low as 25 hl/ha, although Yquem might claim 9 hl/ha, or approximately one glass of wine per vine. For this reason botrytised wines should be astronomically expensive; fortunately for those of us who appreciate them, they are still unpopular with the majority of wine-drinkers, and prices remain in check. Sauternes may in most cases be obtained at prices largely in line with that charged for the red wines of Bordeaux. Tokaji is also reasonably priced, although as quality recovers following liberation from Communist rule prices continue to edge upwards. Select German wines, however, do reach astronomical prices at the nation's wine auctions.

Key points

The true origin of Botrytis in winemaking probably lies in wine prehistory

Botrytis cinerea causes grey and Noble rot; the type depends on local conditions

Botrytised grapes demand several tris and inhibit the progression of fermentation

Despite these difficulties, and low yields, many such wines remain fairly priced

Once harvested, Nobly rotten grapes can present some challenges in the winery. Grapes devoid of juice are difficult to press, and the winemaker may need to persevere with several pressings in order to produce a respectable volume of wine; the first pressing is of highest quality, although the second is richer in sugar, as is the third, although by this time the juice may be suffering from oxidation and have to be discarded. Secondly, a must so rich in sugar can be slow to ferment, as this inhibits the action of the yeasts. It is also feasible that such a heavy presence of Botrytis cinerea may in itself be responsible for slow fermentation; the organism does yield botryticine, an antimicrobial substance which is thought to inhibit the action of yeasts during fermentation. Much may be done in order to encourage fermentation, including warming the fermenting must if this can be achieved. Once started fermentations may stick, although some estates still find sulphur necessary, both to stop successful fermentation and to try and protect against refermentation of the high residual sugar in bottle.

My personal preference for botrytised wines centres on Sauternes, and the Loire, both regions which have a heavy presence in my cellar. Nevertheless, I do have broad-ranging experience, having tasted botrytised wines from Germany and Tokaji, as well as Chile (where Concha y Toro have begun producing a convincing and good value wine), South Africa (Dellrust's Jerepigo gives the double-whammy of Noble Rot and mutage fortification with spirit), Australia (de Bortoli's Noble One being the Yquem-emulating archetype) to name just three. The spread of this style of wine to every wine-making continent - even if some winemakers must resort to spraying Botrytis spores onto their fruit themselves - is testament to how desirable these wines have become. (27/9/05)

Next instalment: Late Harvest Wines, more than just hang-time.