There are a lot of well-meaning bakers out there who publish elaborate recipes for exotic-sounding starters, many of which are based on organic fruit. Why? Because as I mentioned previously, many types of fruit are covered in naturally occurring yeasts. Grapes, plums, blueberries, cherries, blackberries, mulberries, elderberries…all are awash in fermenting fungi. Not by coincidence, they all can be (and often are) made into wine. They are also plausible sourdough starter cultures. However before you go getting excited about making an elderberry bread starter, remember it’s the microbes that lend flavor to a sourdough starter, not the fruit. An elderberry starter will in no way make your bread taste like elderberries.
Fruit starters are made as you might think: by crushing the fruit and adding a flour-water slurry, usually a couple of times a day for a week or more. Why not do that instead of the method I describe? For one because it’s more complicated. For two because it takes longer. For three because it’s easier to culture molds and bacteria that you don’t want. And when you factor in that it’ll probably be the yeast from the flour that ultimately wins the battle for dominance, it’s difficult to see the point in going to all that trouble.
Nope, flour and water. It’s all you need.