Saturday, March 31, 2012

Footnote to Lunotte: A chemistry lesson

The previous blog post on a natural wine from the Loire brought us into the realm of natural winemaking, the subject of numerous books and a robust and occasionally acrimonious debate within the wine world. The term itself is contradictory. Winemaking is no more a "natural" process than curing meat or pickling vegetables or preserving fruit by making jam and is indeed complicated enough that there are entire college programs devoted to its study. Many natural winemakers are graduates of such programs, the preeminent American example of which is the University of California at Davis.

MFWC did not go to Davis and had trouble understanding high school chemistry, so the following explanation, cobbled together from the Oxford Wine Dictionary, will not be a review of the chemical transformations involved in fermentation. Instead, it will emphasize the numerous choices that confront winemakers as they take the grapes from their vineyards and turn them into wine.

The basic concept is simple. Sugar is converted into alcohol (ethanol) and carbon dioxide through the oxygen-free metabolism of yeast. The sugar, of course, comes from the grapes that are crushed into must, which differs from juice because it includes stem fragments, skin, seeds, and pulp. The vintner has to decide what grapes to plant and when to pick them, since the later they're picked, the more sugar they'll have. He also has to decide whether to include the stems, which make for a more tannic wine, and, in the case of white wines and roses, how long to expose the skins to the juice. He also must choose the container in which the fermentation will take place: stainless steel, concrete, or wood. Old oak or new oak? French oak or American oak? What size is this container going to be? All of these issues are the subject of considerable thought and discussion even when their effect on the final product is unclear and may not be understood scientifically.

Yeast turns out to be even more complicated. There are numerous yeast species, and their classification remains a scientific puzzle. Saccharomyces cerevisiae is the species most frequently used for making wine and beer and leavening bread, and there are several hundred strains of it. Making matters even more complex, there are wild yeasts to which grapes are naturally exposed as they grow as well as over 100 different kinds of cultured yeasts that are added to the grape juice. Cultured yeasts are favored for their predictability and essential for producing a wine with more than about 5% alcohol, since most natural yeasts die above that level. Natural winemakers like to let the natural yeasts work early in the fermentation process, though it's again scientifically unclear whether that has any effect on the end product.

So we have grapes and yeast. In addition to carbon dioxide, the fermentation process also generates heat that can kill the yeast and thus halt the fermentation. This is where the vintner's decision about the size of container becomes important. The larger the container, the greater the need for refrigeration. (To reference the preceding post, remember that the Lunotte is fermented in a relatively small container.) The fermentation of red grapes takes four to seven days, while that of white grapes can take weeks, which adds to the challenge of making white wine, since the process must be watched and managed for much longer.

Fermentation is a complex process, and sulfur - really sulfur dioxide - helps winemakers control it by killing bacteria and wild yeast and fostering a rapid, clean fermentation in part by preventing oxidation. Literally 99%+ of all winemakers use sulfur in this way. But sulfur has a very unpleasant taste, and so lower levels of sulfur are desirable in any event. Sulfur dioxide may also combine with other compounds in the wine, whereby it loses its noxious smell but also its beneficial effects. Here I can only quote the Oxford Dictionary: "Good winemaking practice aims to maximize the free to bound ratio of sulfur dioxide; this permits winemakers to add less total sulfur dioxide to achieve the same level of protection for the wine." Hence the natural winemakers' focus on "sans soufre," which is not a virtue in itself but a reflection of careful winemaking.      

The scientific here thicket becomes dense very quickly, but the central point should be clear. The wine you drink, whether it's Chateau Lafite or Yellow Tail, is the product of numerous choices by the winemaker as well as a series of chemical processes that may not be well-understood even though they're the product of intense study and dialogue. Moreover, the means by which winemakers try to spur those processes change over time, just as tastes in wine change. A wine like Lunotte is fascinating because its maker is trying to make some of his decisions clear, which helps explain not only why his wine tastes the way it does, but why other wines may taste the way they do.  


1 comment:

  1. Chemistry is one of the disciplines of science. It colours our life with the discovery of different hidden colours of nature and all the things necessary for making our life happier. The study of chemistry is a must for the advancement of society and for making mankind happier. Chemistry is concerned with rocks, minerals, non-minerals, air, water, plants, animals, other materials of organic origin earth atmosphere, interstellar atmosphere.