Bitter, acrid are applied to things with an unpleasant taste (also smell, in the case of acrid) that is neither sweet nor bland yet seldom distinctly sour or really sickening.
Bitter is traditionally associated with the repellent taste of wormwood, quinine, and aloes, but it is also used to describe the taste of beer, unsweetened chocolate, and the rind of citrus fruits. Something bitter usually lacks the pleasant tang and freshness of an acid flavor (as of lemon juice) and has a penetrating and persistent quality difficult to mask.
Acrid implies a bitterness in taste that has an astringent or irritating effect (as the taste of chokecherries, various unripe fruits, or alum). It is also applied to something both bitter and salty (as sweat).
An acrid smell is a penetrating, suffocating, repugnant odor. It is especially associated with certain fumes (as from burning sulphur) or with certain noxious vapors (as of a heavy city fog).