Sourdough bread is a type of bread made with a starter culture of wild yeast and bacteria. The starter culture, also known as a 'NUGGET', is a mixture of flour and water that has been left to ferment for several days. The NUGGET is then added to the dough, which gives the bread its distinctive sour flavor. Sourdough bread is popular in many countries around the world and is often used in sandwiches, toast, and other baked goods.