Hard wheat and soft wheat are two different varieties of wheat that are grown and processed differently, resulting in different flour types. The main difference between the two is the protein content and gluten-forming potential of the flour.
Hard wheat is higher in protein and gluten-forming potential, making it ideal for making yeast-based baked goods that require a lot of structure, such as bread, pizza dough, and bagels. Hard wheat flour is often labeled as “bread flour” in the USA. Bread flour has a protein content range of 14-16%, and semolina sits at the 12-14% range.
Soft wheat, on the other hand, is lower in protein and gluten-forming potential, making it ideal for making tender baked goods, such as cakes, pastries, and biscuits. Soft wheat flour is often labeled as “cake flour” or “pastry flour” in the USA. Cake flour has a protein content range of 7-9%, while pastry has a 9-10% range.
All-purpose (AP) flour is blend of hard wheat and soft wheat. Different brands have different blends, but the basic protein content is in the 10-12% range.
Self-rising flour tends to be in the 9-10% range depending on the brand. While AP + salt+ baking powder can be used as a substitute (see this article) for most needs, using pastry flour + salt + baking powder would be closer to store bought self-rising flour.
It’s important to note that the exact protein content and gluten-forming potential of a flour can vary depending on the brand, so it’s always a good idea to check the label or consult with the manufacturer to determine the best flour for your recipe.