I am an amatuer at fermenting, so I really don't feel qualified to give knowlegable information. I am passing along my experience of how I make my fermented fresh pressed veggie juice.
I use fresh pressed veggie juice. Each week I juice 14 pounds of cabbage and 2 pounds of carrots to ferment, which makes about 4 1/2 quarts. I ferment immediately after juicing. (I actually drink this much in a week!)
I use wide mouth mason jars. I clean them, but don't sterilize per Tim Hall's suggestion on the post "Surface Mold on Sauerkraut". And what he has explained there is of utmost importance to this process.
For veggie juice, I use Body Ecology's Culture Starter, 2 packets per 6 quarts juice. This gives a big dose of the good bacteria right away as Tim suggested. With this starter, only low carbohydrate veggie juices can be used (cabbage, a few carrots, lettuce, celery, etc., but no beets). The L-Plantarum, which is in the culture and also is the predominate bacteria to culture veggies, can't handle much sweetness. I fill the jars up to the outside rim. I use 3/4 tsp. french celtic sea salt per quart because Sally Fallon suggests it! Some say it helps keeps the unfriendly bacteria from growing, others say it doesn't. I like to be on the safe side. Then I cap the jars.
There are two methods of setting aside to culture:
1. I then put these jars in my "culture closet" with a towel over them. I let this ferment at about 70 degrees (maybe 74 degrees) for 2 days. Since this is a "controlled" fermentation, meaning that I started with a culture, it takes less time. After that time, when I open each jar, some of the fiber has risen to the top. On the very top layer, there is a "discolored scum", which is the veggie fiber discolored from exposure to the oxygen in the top of the jar. Simply skim the scum. I then stir each jar, put a on a cap (not an air tight one, just a screw on), and refrigerate. Keeps for months in the refrigerator.
2. Or leave the jars on the counter and cover with a towel. Stir about every 12 hours to stir in the fiber that rises to the top. This way there is no skum to skim. Recap each time and also cover with a towel (they like it dark). Let culture the same amount of time, which is 2 days.
(I don't know how to do this without the culture starter.)
I haven't experimented with high carb veggie juice and fruit juices yet. I feel confident that a keifer starter would work, just like in coconut keifer.