Sun-Loving -- Within Reason

• California Zin may grab the lion's share of the world's attention, but it can be grown on other warm, well-drained hillsides: Australia and Mexico both produce Zinfandel in small to moderate volumes. California still dominates the market, according to the 2012 California Grape Acreage Report. In that survey, Zinfandel emerged as the the third-leading varietal in California, representing more than 47,000 acres of Zin-specific vinelands.

  That prevalence is in no small part due to California's sun-dominant climate, which produces a red table wine with an alcohol content between 13 to 15 percent. The versatile grape can shift in character from light-red “summer picnic wines” to robust, dry affairs to punchy dessert wines in the style of port. As much as the wine's character is defined by sun, it can be utterly destroyed with an overabundance. The reason for this lies in the science of viticulture and wine craft.

Everything in Balance

• All grapes need heat to ripen. As a rule, Zinfandel ripens late, and it ripens unevenly. If you look at bunches of Zin hanging on the vine at harvest, you'll notice that the bunches are multicolored, with dark red grapes and bright green grapes interspersed with the occasional shriveled raisin. Because of this tendency, a long sunny season is necessary to bring about the fruit. However, the varietal responds ironically poorly to continuous warm weather. For best ripening, Zin requires "diurnal" temperatures -- reliably warm days and reliably cool nights.

Overripe Fruit

• When the growing season is too hot for Zin grapes to handle, they tend to sprint to the ripening "finish line." This quickly leads to overripe fruit. Zin created from overripe grapes tends to have a "raisin" bouquet, as opposed to the fresh cherry subtleties fans prize.

Dry Grapes

• Extreme heat can sear grapes on the vine, leading to unusable clusters of raisins. One example of this was in the heat wave that swept the growing region in southeastern Australia in 2009. As temperatures spiked above 104 degrees Fahrenheit for more than a week, breaking an all-time heat record set a hundred years before, the sun decimated grape yields by drying the fruit as it hung. One winemaker reported that his vineyards appeared as though "someone [had] taken to it with a flame-thrower."

Too Much Alcohol

• Like all red wines, hot, dry climates can lead to rapid sugar accumulation in Zinfandel grapes. This has two-fold importance to the process of fermentation. As fermentation involves the conversion of sugar into alcohol, overly high-sugar grapes invariably become wines that "burn" with an overabundance of alcohol. These wines are generally regarded by expert tasters as lacking balance and displaying a one-dimensional sweetness that overwhelms any other subtleties once present in the wine.