Cold brew is forgiving in technique, but it's ruthless about inputs. Because the extraction is slow and the drink is served chilled, minor defects in the bean or roast can become very obvious, like papery astringency, muddled aroma, or a finish that overstays its welcome. The upside is that smart quality choices show up fast when you know what to taste for. Done well, you get a clean, mellow profile with real sweetness and a steady body.