Sugar Levels vs Alcohol is an old winemaking debate. The grape inherently has a certain amount of sugar that the winemaker can ferment and turn into alcohol through the action of yeast. The longer the fermentation goes on, the lower the sugar and the greater the alcohol. Winemaking styles, both individual and regional, further complicate generalizations.
Wines also are made sweeter through the addition of sugars. Sometimes it is because the grapes in a bad year beg for it. Sometimes the public having been now accustomed to the modern diet, demands that sweetness. The French allow winemakers to add, in a bad year, measured amounts of even sucrose. California does not allow that but allows the addition of fructose (fruit sugar) generally even to create a flavor profile. Same difference?
One way to express the potential alcohol in a wine is a measurement called degrees brix. It looks at the grams of sugar, both glucose and fructose, contained in 100 grams of the total juice. Then you multiply the brix times a factor of .55 - .60 (generally .60 is used for white wines fermented at colder temperatures) and you arrive at the potential alcohol of the wine. For example, in 2013 the average brix of chardonnays harvested in California was 23.8 degrees. Since most Chardonnay today is cold fermented, we have .60 x 23.8 or 14.28 % potential alcohol. That doesn’t mean that the winemaker is going to make a wine with 14.28% but he could. The price he pays is that he has to ferment to total dryness. This is how our same chart would look for whites by varietal by potential sweetness in the grape.
For the year 2013, California state averages, a Chenin Blanc was potentially the driest and Viognier was potentially the sweetest grape.
Pinot Gris/Pinot Grigio
Sauvignon Blanc/Fume Blanc