I have become interested in the methods for lacto-fermenting, using  old traditional (no hops) brewing but adapted to modern situations. I made several lacto-fermentation tests. They all came out varying degrees of fine after varying amounts of time.

I would suggest to anyone interested in lacto-fermenting beverages do the following:

Make a cup of tea and add 2 Tablespoons of sugar. Stir until dissolved. (If you make kombucha, use your sweetened tea. If you are an herbalist, add any herbs from your garden that you like.)

Mix the tea with an ale starter and a lacto-fermenting starter. If you make kefir, the simplest way to do this is to mix it with some kefir whey. If you don't have kefir, make some whey from some yogurt by putting yogurt in a clean cotton flannel bag (like a jelly bag) or 4 layers of cheesecloth/muslin and let it drip overnight. Take the yogurt whey and mix it with a little ale starter  and add this to the sweetened tea. I have also used plain yogurt whey with no ale starter and it fermented the brew but it took a lot longer. I don't know if the entire fermentation was from the lacto-bacteria or if there was some yeast contamination in the bottle. But the end product was OK.

Next, put the liquid in in a clean plastic soda (pop/fizzy drink) bottle and
screw the cap on tight.  Set it in a warm place and wait.  When you can't squeeze the bottle, it is ready to drink.

After you drink it, you can make your own adjustments to taste for  your next batch. If you want it sweeter, add more sugar, for a beer-ier taste,  add malt extract to the sugar. For more alcohol -- and you can make a fairly potent tipple here to almost the amount of alcohol in commercial wine -- see my page on adjusting alcohol. If you want more flavors, add some more herbs and spices to the tea next time. Whatever you have in your kitchen and garden will probably do because they are what you like best.

 Some observations:

Kefir whey carbonated sweet tea in 3 days; yogurt whey took about 7 days.

Using leftover beverage as a starter for the next bottle works fine, but I suspect it is mostly a yeast ferment. I don't know if there is a way to keep the lacto-bacteria in balance or I will just have to use new whey every batch. Of course, the yeast-heavy brew tastes just fine, too.

I also have some brew started using sauerkraut/kimchi liquid that was started with whey (and thus didn't need salt). I don't know if it was kefir or yogurt whey. I'll have to start paying attention. The brew seems to be coming along no problem.

Adding a teaspoon of malt extract to the sweetened tea adds an extra layer of creaminess to the final product.

Adding extra sugar or malt and not screwing the cap on tightly but letting off gas (burping) for 2 or 3 days before setting cap on tight would increase the amount of alcohol in the drink.

The only real purpose of fermenting it first in a vented carboy would be to increase the amount of alcohol in it, and if you fermented it in a unvented carboy (to begin carbonation immediately) you run the risk of the carboy exploding (why I always carbonate in plastic).