Before going gluten free, I used to make this rye bread as a staple. After some failures I succeeded in making the perfect starter which lasted a very long time and got better every time I used it. The secret of sourdough is that it makes the bread more storable. Bread made with sourdough will not become stale for quite a long time, and due to different fermentation many micronutrients can be better resorbed than from yeast bread. The quality of a sourdough depends on the quality of the grain and the mixture of yeasts and bacteria present in the flour. If the rye flour you use is neither chemically treated so that the natural cultures are killed nor contaminated with wrong bacteria, yeasts or mold, you will have a starter which keeps forever when properly kept and fed. The texture of the starter should be creamy, and the smell slightly sour, but not stinging the nose like vinegar. If it smells like vinegar, it contains too much acetic acid which is not desireable. The ration lactic acid - acetic acid should be about 80 to 20. That makes a delicate sour smell. If it smells rotten or looks reddish, it is rotten and you have to discard it.