I'm halfway to achieving the same goal but in a different way, using Algae.
The thing is, both Algae, Kefir and other specific bacteria for this goal need an aerobic environment. If you put the lid on algae and up the nutients you can produce a toxic algae. If you do the same with Kefir you change the environment, reducing oxygen and helping the bacteria you don't want. If you then eat this, you'll get gas... or worse! Trust me, I know!
As a result of this it's quite hard to transport Algae and Kefir.
So I've been thinking hard about how to design something to help transport it.
I have a partially working solution - a one way valve... but this doesn't let in enough air for the culture to survive for more than a day... and it effects the taste, taking a while to recover.
What is required is a vessel that can hold a liquid but truely keeping it oxygenated with the air outside. How can we design something like that?
I looked at goretex but then relised that's the opposite of what we need and it didn't seem to work in reverse.
The next idea was a 3D rotational sphere, able to rotate in all 3 planes... however that wouldn't work against vibrations.
Any thoughts on how to design this thing?