When oxygen hurts — old wines
Older the wine, less time in the decanter. Old red wines have a different problem: color pigments and tannins bond and fall out of solution, creating sediment that's harmless but tastes gritty.
Unlike young wines (splash, aerate), old wines need a gentle pour, minimum air. The classic ritual: stand the bottle upright for 24–48 hours, place a candle or flashlight under the neck, pour slowly. The instant the sediment reaches the bottle's shoulder, stop.
5–15 years old → 5–15 minutes. 15+ years → 5 minutes max, drink immediately. Vintage Port → 30–60 minutes (Port is durable).