If you are or know a barista, here’s a tip: grind the espresso as you need it. Don’t let the grinder run until you’ve got half a pound of pre-ground espresso sitting around getting stale. Seriously. If I see you doing that, I’ll just walk out.

The reasons are myriad, but it all comes down to quality. Not only does prolonged exposure to oxygen make coffee go stale, ground coffee absorbs moisture from the air and swells. Espresso is very finely ground, about as fine as table salt. If it swells, the extraction will be all wrong. If it’s stale, then what’s the point?

With espresso more than most other methods of coffee preparation, details matter. There’s not a lot of room for error. The beans need to be fresh, but not too fresh. The grind needs to be right for the air conditions. The ground coffee needs to be tamped properly (not too hard, not too light). The water quality, temperature, and pressure are critical. The length of extraction — how long water is in contact with the grounds — is a deal breaker. It must be consumed soon after brewing. Mess up any one of those elements and you’ve ruined the experience. It’s the experience of espresso that sets it apart.

So please: you might think it’s saving time or wear on the grinder to pre-grind the coffee, but it’s not worth it.