Sourdough bread comes in many types, depending on the flour used, and this makes a dense rye loaf. In any case it is made with a sourdough starter, rather than packaged yeast, which uses the yeasts that occur naturally in the atmosphere and on flour. It takes time to 'grow' the starter, but then this is not a difficult bread to make, and if you feed your leftover starter you can continue to make more loaves.
Leftover sourdough starter can be stored in an airtight container in the fridge. Before using it to make another loaf, bring it back to room temperature, then feed it once as in the main recipe and leave for about 6 hours. Each time you make a loaf, you will have leftover starter. This can be kept in the fridge, feeding it every 4 days to keep it alive, and will improve in flavour. Any starter you do not need or want can be discarded, or given to a friend.