Start with clean gear. Wash your brewing vessel, filters, and jars like you’re preparing for surgery. Any leftover crud from last week’s batch is an invitation for spoilage. Cleanliness is next to coffee-ness.
Don’t double-dip. If you pour a glass, pour it into a separate cup—don’t drink straight from the jar. Your mouth has bacteria (we all do), and it’s basically shaking hands with your cold brew. Keep ’em apart.
Keep the fridge cold. Aim for 35–40°F (1.5–4°C). If your fridge is a bit warm, your cold brew will age faster, like a vampire in the sun. A fridge thermometer costs five bucks—worth every penny.
