Packaging
Keg
A sealed pressurised container that keeps beer stable for months, with no air contact during dispense.
A keg is sealed and pressurised, and the beer inside is pushed out by carbon dioxide or a nitrogen blend rather than by a hand pump drawing air in. Nothing but gas ever touches it, which is why keg beer is stable for months where cask is stable for days.
The beer is usually filtered or pasteurised, and carbonation is set by the brewery rather than developing in the container. That consistency is the trade-off keg offers: less of the soft, gently carbonated character cask conditioning produces, and far less risk of the beer being ruined between the brewery and the glass.
What replaces the beer as it leaves
- The cask is vented. A peg is driven into the top and the beer inside sits at atmospheric pressure. As each pint is drawn, air enters through that vent to take its place — and because oxygen is what stales beer, the working life of a tapped cask is measured in days, typically three at best.
- The keg is sealed. Nothing enters but carbon dioxide from a cylinder, which pushes the beer out. Air never touches it at any point between the brewery and the glass, and the beer stays stable for months. That is a consequence of the seal rather than a judgement about which beer is better.
How well it protects the beer
| Light | complete. Opaque, so no light reaches the beer. Lightstrike is not a risk in this format at any point. |
|---|---|
| Oxygen | very low. Very little oxygen crosses the seal. Staling is driven by whatever oxygen was picked up at packaging rather than by ingress afterwards. |
| Conditioning | Beer does not referment in this container; carbonation is set before or at packaging. |
| Material | steel |
| Typical volume | 30000–50000 ml |
Other formats
- Aluminium can — complete light protection, very low oxygen ingress.
- Brown glass bottle — good light protection, low oxygen ingress.
- Cask — complete light protection, high oxygen ingress.
- Clear glass bottle — none light protection, low oxygen ingress.
- Green glass bottle — poor light protection, low oxygen ingress.
- Mini keg — complete light protection, low oxygen ingress.
See the side-by-side table on the packaging index, or how this plays out over time in storage and freshness.
Last reviewed 2026-08-15.