Sourdough bread is generally made from flour, water, and a starter culture of wild yeast and bacteria.
These ingredients are all biodegradable and compostable.
The packaging that sourdough bread is sold in may also be compostable, depending on the materials used.
For example, if the bread is sold in a paper or cardboard bag, it can be composted.
However, if the bread is sold in a plastic bag or wrap, it will not be compostable.