Sugars
To produce alcohol in wine at least one type of sugar must be present. It could be fructose, glucose, dextrose or dozens other different types which occur naturally in most fruits. Also present in many fruits and honey is the sugar, sucrose. Sucrose may be added to your must in the form of common white cane (table) sugar.
Beer brewers know to use only corn sugar in their wort, or their beer will taste cidery and off. Unlike beer yeasts, wine yeast is not particular about the type of sugar you use. Wine yeast can totally digest most basic sugars. This is a bonus for the home wine brewer, as corn sugar is about three times as expensive as regular sugar.
As a general rule,
you should adjust red wine musts to a specific gravity in the
range of 1.080 to 1.095. White wines are usually within a range
between 1.070 to 1.085. Do not attempt to produce wine with a
potential alcohol level above 14%. Many wine yeasts will not
survive in liquids with more than 14% alcohol. It is easy to add
too much sugar. What you will then have is a strong wine with too
much residual sugar, thus making it oversweet and undrinkable. It
is better to stick within the aforementioned guidelines,
ferment to dryness, and then stabilize your wine (1 gram or 1 ml
of potassium sorbate and 1 Camden tablet per gallon) and then
sweeten to taste.
Sweetness must be balanced with acidity, and vice versa. A sweet wine must have a relatively high acid content, to cut the sweetness and give the wine a finish. Otherwise the wine will taste insipid. Generally, high acid wines (most but not necessarily all) must have some residual sugar to impart smoothness, add balance, and round out what would otherwise be a harsh wine.
Note: 1 cup of sugar weighs 210 grams. 114 grams of sugar will raise the specific gravity of 1 gallon of must .010; i.e., from 1.050 to 1.060. 114 grams of sugar is a little more than ½ cup. Always add sugar slowly (in small amounts) and, after each addition, stir well before taking a specific gravity reading. It’s much easier to add more sugar than to try and correct a must which has been over sweetened.