Noble Rot: A Quirk Of Nature That Yields Great Wines

January 26, 1989|By Patrick Fegan, Copyright 1989 by Patrick W. Fegan.

One of the icons of the wine lover is ``noble rot,`` an oxymoronic term referring to a peculiarity of nature that results in the world`s greatest sweet white wines.

Wines affected by noble rot, a mold, were discovered barely three centuries ago by a tardy-and noble-man.

It seems that harvesters of the Middle Ages were not allowed to pick grapes until someone important said it was OK. But it had to happen: a local big shot in the Germany of the 1700s was late getting back home to OK the start of picking. While the vineyard workers fretted, the grapes were attacked by rot and began to look more like brown mice on a branch than bunches of grapes.

When the big shot finally arrived, it was too late to make normal wine but he had his workers gather the grapes anyway. To their surprise, the resulting wine, a totally new style, was luscious. They christened this rot

``noble,`` or edelfaul in German, and the rest is history.

Today`s great Beerenauslesen and Trockenbeerenauslesen are its descendants. The practice spread to France and other parts of Europe and, more recently, to the New World, where botrytis wines have developed a small following.

Botrytis cinerea, also known as grey rot, is a fungus that infests vineyards throughout the world. Usually winegrowers try to destroy botrytis, as it attacks semiripe grapes and gives them off-flavors that can be translated into the wine. If it is caught in time, grey rot can be killed off or at least stymied by the use of copper sulfate or other anti-fungal sprays. However, in a few peculiar vineyard patches, grey rot can turn out to be noble rot (the French call it pourriture noble) if it attacks late in the season and if it is subject to the proper cycle of climatic changes.

First, there must be a period of moisture-the morning mists of a nearby river, for example. Then, before the fungus gets too strong a moldhold, there must be a period of sunshine to dry it and effectively control it-a sunny afternoon. If this cycle persists, botrytis will continue to develop but will not do its normal damage. Instead, it will pierce the grape`s skin (how many grapes or bunches are affected will depend upon the capriciousness of the weather) and send tentacle-like limbs into the pulp. Physically, the broached berry will evaporate water and shrivel, ultimately resembling a furry, yellow- brown raisin; this concentrates both the sugars and the acids in the grape with respect to the remaining water.

So, where a normal harvest might include grapes with a sugar percentage of 22, a botrytis-affected crop might be 30 to 40 percent sugar or more. Because of this shrinkage, yields are significantly reduced: where an unaffected vineyard will yield 4 or 5 tons per acre, a botrytis-affected one will yield 1 to 1 1/2 tons, often less.

Since botrytis doesn`t affect each berry or each bunch at the same time or at the same rate, in order to pick the most concentrated grapes, workers must go over the vineyard several times, selecting those and leaving the rest to further shrivel. It is not uncommon to see vineyard workers selecting single berries from a bunch and returning days later to gather a few more.

However, because that is economically impractical, the practice at most properties is to wait as long as possible and then pick everything, hoping to get the most overripe, shriveled berries together with unaffected or partially-affected fruit. This, however, can be risky in areas like Bordeaux where ruining, late-season rains are common. This risk, combined with the reduced yield, can only make such wines rare and expensive.

In the winery, the grapes are pressed-sometimes giving a single drop per berry-and their sugar-rich juice is left to ferment. Because there is so much sugar, the enzymes in the yeast become exhausted before they can convert all of it into alcohol, carbon dioxide and heat. Hence, when the wine has reached an alcohol level that ranges from 6 percent in Germany to over 13 percent in Bordeaux, it still has lots of natural grape sugar left. The result is a moderate to highly alcoholic and quite sweet wine.

Because the finished wine is so sweet, tart and young, it needs time to become integrated: drinking just-finished Sauternes, for example, can be a painful experience because the rough sugar, acid and alcohol mixture actually tastes hot.

Aging takes place in vats or barrels (brand new 60-gallon barrels for 3.5 years at Chateau d`Yquem) and then the wines are bottled. The lighter-weight wines from little-affected grapes can be consumed with just a few years` aging in the bottle. The rich years, however, give wines that need 10 or 20 years before they really peak. You can certainly drink them young-the wonderful 1983 Sauternes are examples-but they repay patience extremely well.