I'd like regular ancestral cooking emails!
Two ingredients, old bread and sugar, and you can have Russian Bread Kvass.
I find home-made sourdough rye and some very dark brown sugar pretty unbeatable taste-wise. And I use the bread cubes again and again, brew after brew, so that they become a bit like kefir grains – a colony of probiotic yeasts and bacteria.
Here are the said bread cubes being filtered out as I pour the fermented liquid into a swing-top bottle for a second fermentation.
My favourite flavouring for this second ferment is raisins and mint. But orange and ginger are good too.
Some more pictures in my story today and the recipe (which includes videos) is the top link in my profile.