I'd imagine that the taste only comes after the Shout (for it is difficult to taste something that is erupting from your lips at such a speed), and that it varies by Shout. Would Frost Breath leave a minty aftertaste? And would Disarm bring the taste of whatever weapon your foe held, be it steel or ebony or anything else, and would Bend Will's aftertaste be that of bondage with a hint of dragon, blood and tears and scales?
Or perhaps they all leave an aftertaste of sulfur, or domination, or void salts, or Kyne's sweet wind?