Cold brew tastes sweet, but black coffee has little detectable sugar. Why?

Answer: Less taste masking

Extra dissolved sugar — Almost, but black coffee is not sweet mainly because it dissolves table-sugar-like material. Coffee researchers note that sweet sugars sit below human detection thresholds, so the sweet impression usually comes from caramel, fruit, and roast aromas. Cold brew can feel sweeter because bitter and sour signals are quieter.

Less taste masking ✓ — Right. The surprise is that cold brew's sweetness is mostly subtraction, not added sugar. Sensory work links coffee sweetness to caramel or fruity aroma concepts and to the absence of bitter, sour, and burnt notes. Cold brewing often lowers acidity and bitterness, so the brain reads the same black drink as rounder and sweeter.

Stronger caffeine bite — Not quite. Caffeine is bitter, so making it more prominent would usually push the cup away from sweetness. Studies also find caffeine results depend on recipe, time, and method rather than a simple cold-equals-more rule. The sweeter impression is better explained by weaker sour/bitter masking plus aroma associations.