These green oxygen barrier crown caps are perfect for your bottling needs! The crown caps crimp over standard lipped beer bottles to create a seal, keeping carbonation in and oxygen out. The green color also helps you to color code your different batches. These caps have an oxygen absorbing lining that helps to keep beer safe from the oxidative effects of oxygen in the headspace that can lead to stale beer. They are an ideal way to keep your beer fresh for as long as possible!