Saltiness is the Taste produced by sodium chloride (and other salts).  As with food, the perfect amount of Saltiness can make Flavor come alive; too much can ruin; and too little can make Flavor fall flat.

Sweetness is typically produced by the presence of sugars in a substance.  Sweet flavors in natural (un-flavored) tobaccos can be subtle or pronounced.   Some tobaccos, like Virginia tobaccos, naturally have a higher sugar content than others.  Alternately, the Sweetness can be coaxed out of tobaccos through fermentation and curing methods; as with Maduro cigar wrappers.

Sourness, or Tartness, is an indicator of Acidity or Acids in a substance.  Too much Acidity will overwhelm the palate (sense of Taste) and inhibit the true flavors of tobacco (or any other delicacy) from emerging.

Bitterness is usually an indicator  of Alkaloids or of an Alkaline substance.   The Taste is usually characterized as dry and/or astringent; similar to the flavor of black coffee or quinine (tonic water).  Among other effects, tobacco fermentation releases ammonia, which is an alkaline compound.  Ultimately, extreme or unbalanced bitterness in tobacco will taint the other flavors and finish.