All-purpose, or plain flour, is a blended wheat flour, less refined than pastry flour, with a protein content slightly higher and rich in gluten, minerals and starch, as it is, as I wrot, less refined and blended with some bran too. It is reccommended to get elastic, tough doughs, so it is great to make bread, fresh pasta, brioches or pizza, even if the rising time will be quite long. It is usually considered a medium-hard flour, with a “W value” > 250, versus the w > 170 of pastry flour. But there are also stronger all-purpose flours, with w > 350: in Italy, the most used flour of such strength is usually North American wheat-based. We call it manitoba, it is obtained by milling and processing varieties of wheat grown in the Canadian region of Manitoba. It forms a very high quantity of gluten during the kneading and cooking of the bread, so it is used to make Panettone and Colomba, for instance, which need a very strong flour. As per its nutrition facts: 325 kcal- 1380 kj, 9.0 g protein, 74.0 g. carbohydrate, 1.0 g. fat.