 If this job isn't done right, then everything else has been a waste of time. So in some ways this is kind of the most important job. The oxygen is obviously bad for the beer because it will oxidise the beer and potentially cause it to have a limited shelf life and go off quicker than otherwise would do. So when we're running the beer from the fermenter into the conditioning tank, oxygen is our enemy if you like. So what we do is we flood the tank with CO2 first. And that CO2 is obviously heavier than air. So because it's heavier than oxygen, it will drop down and it will push any of the oxygen further up the tank if you like. So once we've done that, we can then start to run the beer through into the tank. Now the beer is heavier than the CO2, so the beer comes in from the bottom, pushes the CO2 up and that pushes the air up and basically you are essentially creating a top layer of pressure if you like, a top layer of CO2 which will provide protection for the beer. The issue with cats in a way is when you've got them in the pub, I assume once you've opened them you've exposed it to the air. Exactly. So how do you counter that problem or is it just a case of selling the beer? The way, exactly, the way with Cascale, because it's not fourth carbonated, there's no CO2 going in, it's just ideally sell it within three days and that's the kind of lifespan you've got from when you tap the cast. In a keg, which is different you have, the beer would be under carbon dioxide pressure that is also carbonating the beer, that's adding the bubbles or is that just to prevent the air from getting in? It would do, yeah. And it obviously means that it's not exposed to any air at all so the product has a longer shelf life.