Causes of dryness
Dryness in alcoholic beverages can occur in low-gravity worts or musts where there is little sugar overall, or when a yeast is too attenuative for the gravity. It can also be the result of a bacterial or other infection, since spoilage organisms can often ferment sugars that are unfermentable by ordinary beer or wine yeast.
The easiest way to avoid dryness is to balance the gravity of your wort or must and the attenuative character and alcohol tolerance of your yeast. However, in some cases you can also use back sweetening techniques to eliminate excess dryness.
Beer can be made more dry by using sugars as a portion of the total fermentables. Sugars ferment fully, producing alcohol but little to no residual taste or body. This may be desirable when attempting to produce a very light beer, similar to many macrobrewed american lagers, or for lightening a high-gravity beer such as many Belgian beers. Common sugars used for this purpose are Dextrose and Belgian Candi Sugar.