While water kefir seems to be the rage of the day, I have a few more questions about water kefir. What can we add to it, besides ginger or coconut? For example, can I add liquid minerals
Mineral sources such as nettle leaf or alfalfa herb would be better choices. You can make a tea out of these then use these as your base. Many "trace mineral" products contain too many heavy metals.
or digestive enzymes,
I would not add enzymes. You do not want to digest the kefir grains.
or liquid vitamins to the mix?
Liquid vitamins are garbage. Vitamins are quickly destroyed in a water environment from oxidation.
HV, you said to avoid inorganic fruit due to the sulfur content. Are there any other minerals to avoid? Would herbs be compromised if they were added?
The fruits are organic, it is the preservatives used that are not. Generally this means sulfites, which are used to help maintain the color of the fruits. If you are using fresh fruits then there should be nothing in these I can think of that would cause any problems. Just make sure to clean them well before use. Soaking the fruits in a peroxide water for 15 minutes or so. This will oxidize the herbicide and pesticide residue. Then rinse and dry before use.