The best flour for making and feeding a sourdough starter is typically unbleached flour. Common good choices include:

• All-purpose flour (unbleached)
• Bread flour
• Whole wheat flour
• Rye flour

A popular approach for starting a new sourdough starter is to use a blend of 50% whole wheat or whole rye flour and 50% bread flour or all-purpose flour. Whole wheat and rye are nutrient-rich and help jumpstart fermentation and microbial activity, while bread or all-purpose flour provides a good ongoing food source for the starter. Once the starter is established, feeding it with plain unbleached all-purpose or bread flour is common practice. Rye flour can create a very active starter with more acidity and flavor, and fresh milled whole grain flour is also recommended for strong fermentation. Organic and unbleached flours are preferred to avoid chemicals that may hinder yeast growth. For gluten-free starters, flours like buckwheat and rice flour can be used. In summary, unbleached all-purpose, bread, whole wheat, and rye flours are all excellent options for sourdough starters, with whole wheat and rye particularly good for getting the starter going strong at the beginning.