Sourdough is the most original form of leavened bread. The first recorded use was as early as ancient Egypt. It is believed to have been discovered by accident when bread dough was left out in ambient temperature and good bacteria drifted into the mix, thereby accidentally creating a sourdough culture. The resulting bread had a better taste and texture than yeast-based bread. Also, the fact that sourdough had a long uncooled shelf-life was helpful at a time when refrigeration had not yet been invented.
Rye began as a weed that invaded wheat fields, but proved to be a more efficient and useful grain than wheat. Rye is an ancient grain that thrives in cold and wet weather. Before modern agriculture and transportation made wheat available everywhere, rye was the best - and sometimes only - option for bread baking in parts of northern Europe, including Germany. The climate there is unfavorable for wheat, making rye a better option.
Rye flour contains less gluten than wheat, which is why rye bread is denser and doesn’t rise as high as wheat. That’s where sourdough comes into the picture. Sourdough promotes dough acidification which allows rye bread to rise properly and to obtain a good crumb structure. The increase of acidity from sourdough prevents starches from degrading, giving the bread a longer shelf-life. Rye sourdough bread loaves are dense and crusty, with unique tangy flavors from the long-fermentation process, and they have more nutrients than wheat bread.
Sourdough is popular because it's healthier than regular packaged bread. Sourdough breads don't use preservatives. Studies suggest sourdough causes fewer spikes in blood sugar, improves the absorption of minerals, and is easier on celiac patients.
Rye sourdough is the foundation of German bread, making it one of the best and most delicious bread types in the world.