Cold brew, cold drip, and flash-chill iced coffee

"Cold coffee" covers several genuinely different processes, not one method. Cold brew immersion steeps coarse grounds in room-temperature or cold water for an extended time — typically 12–24 hours — producing a low-acid, naturally sweet, smooth concentrate that's usually diluted before serving; because no heat is involved, fewer heat-sensitive acidic and aromatic compounds are extracted, which is the source of its characteristically mellow profile. Cold drip (sometimes marketed as a "coffee tower" or Kyoto-style) drips cold water slowly through a coffee bed over several hours rather than steeping — closer in mechanism to a very slow pour-over than to cold brew immersion, and often perceived as brighter and more complex than immersion cold brew, though it takes specialized equipment.

Flash-chill ("Japanese iced coffee") is different again: it's a hot-brewed coffee — typically a pour-over — brewed directly onto ice instead of into an empty vessel, so the coffee is extracted hot (preserving the aromatic complexity a hot brew captures) and chilled instantly as it hits the ice, avoiding the flat taste that comes from brewing hot and cooling slowly. The three methods are not interchangeable substitutes for each other — they're chosen for genuinely different flavor outcomes.