Why don’t all beer bottles have screw caps?

The main reason breweries don’t use twist-offs is because they’re not as reliable a seal.  Screw caps don’t create as airtight of a closure, allowing more oxygen permeation. Oxygen is the enemy of fresh beer, so even tiny amounts of air sneaking into your bottle can eventually stale your beer.

There’s also something psychological at work: Because mass-market breweries have long used twist-off caps, some beer consumers still associate them with the Bud-Miller-Coors of the world—and craft brewers want to signal that their products are different.

Ultimately, if you’re making an effort to buy fresh beer, you probably won’t notice the minute amount of oxygen that seeps in under a twist-off can in a few weeks’ time. But some brewers don’t even want to chance it.