are goatskin water bags anaerobic? (kefir related)

[Sal]

Hi guys. I saw some kefir stuff in the kombucha section so I thought I would ask this here, are goatskin water bags anaerobic? The reason I ask is that I read that kefir traditionally had a 1st ferment in goatskin bags and was then transferred into anaerobic containers after for a secondary ferment. Does that mean I should be using an airlock for the 1st ferment?