Edward Fitzgerald's recipe for "Paradise enow", delivered in The Rubaiyat of Omar Khayyam, is "a jug of wine, a loaf of bread, and Thou beside me singing in the wilderness". Bread is a relatively standard commodity and anyone's perfect Thou is a matter of individual taste, but the essence of a good wine, like Paradise itself, is notoriously elusive and ephemeral.
Considered merely as a potable chemical, wine comprises sugars, carbohydrates, minerals, vitamins, polyphenols, aldehydes, ketones, enzymes, pigments, some two dozen organic acids and several kinds of alcohol. It is the infinite number of permutations and combinations of these ingredients that make possible the wide variety of wines available.
Meteorologically too, the recipe is fairly simple. It is widely accepted that the best potential for viticulture lies in between the lines on the map, or isotherms which delineate an average annual temperature of 10 and 20
Celsius. Most wine-producing regions, therefore, are located between latitudes 30 and 50 north or south in each hemisphere, although some wines are successfully produced in regions nearer the equator that are rendered suitable by virtue of their altitude - like Kenya, Tanzania and Bolivia.
Ideally, the mean annual temperature should be about 15 with a summer maximum of 22 and a winter minimum of 3. The temperature at certain critical times of the year should never drop below 10 and extremes of any kind are undesirable. Sustained warmth provides grapes with a high sugar content for conversion into alcohol. Warmer climates, therefore, produce full-bodied wines with a high alcohol content, while a cool climate results in a crisper, fresher-flavoured wine of high acidity. The grapes require about 1,300 hours of sunshine every year to thrive and about 700 millimetres of rain, at the right time of year, for them to grow their best.
Variations in the weather cause wines to vary in quality from one season or vintage to the next. And climatic conditions result in differences on a variety of spatial scales from those between continents to those between adjacent vineyards.
Sun, soil, temperature and water all have a bearing on the mix and even, some believe, the very bedrock over which the vines are cultivated. All these factors, and of course the topography and orientation of the vineyard, combine to varying and undefined degrees to provide what the French call the terroir, the totality of the growing environment of which the wine becomes the ultimate epitome.