When seeking to build your own “wild yeast” starter, called Levain and used to make sourdough breads, you have to regularly feed this new organism living in your kitchen. After a few days in the refrigerator, especially if you don’t feed it with more flour and water, you may develop a grayish/brownish layer of alcohol product, called hooch.
The Levain I have been working on has now indeed taken on the distinct smell of sourdough and has developed some hooch on top of a couple batches.
It’s definitely time to feed a portion of the growing supply of starter, and use up a lot of what I have in baking.