The first thing to go wrong? The steep time. People either forget about it and let it sit for two days, or they try to rush it in 6 hours. Both give you a subpar jar.

Why does time matter? Too short, and you get a weak, sour brew—the coffee hasn't yielded its goodness yet. Too long, and you start pulling out bitter compounds that were better left behind.

Here's your window: 18 hours at room temperature is the sweet spot for most concentrates. If you're in a hurry, 12 hours will work, but it'll be a bit less smooth. And if you forget it? Don't panic. If it's been 24 hours, taste it. If it's not bitter, it's fine. If it is, you've learned your lesson.