I have been wondering whether kombucha needs to ferment in an open air container. Even though a cloth towel is covering the vessel, I know very well that dust, dirt, and micro organisms are able to travel through the “barrier.” Also, the kombucha is sitting in my guest bathroom. And, while the bathroom doesn’t get used, it seems more sanitary if the vessel is hermetically sealed.
In one bucket, I oxygenated the liquid, oxygenated the air, sealed up the top, and then placed an airlock in the hole. In the other bucket, I placed a cheesecloth over the top. After a couple of weeks, the scobies were dramatically different. Clearly, the gelatinous mass is a protection barrier to oxygen.