I have been playing around with fermented pre and probiotics for years, including sourdough.   I make my own goats milk kefir and now I have been working with water kefir, which is really easy to produce with some lovely zing flavours of orange, lemon, ginger and blueberry.  Naturally fermented on kefir grains.  No UPF, just sugar, filtered water, and natural flavours from fruit.  Tasty refreshing and giving the love to you gut and immune system.