What is strong flour?

People love baking bread at home more and more. There is a kind of magic in putting together flour and water and kneading, and home baking is also much cheaper than buying baked goods (bread in particular) at the supermarket. Flour industry has responded to this demand by making more flours available on the supermarket shelves.
In this article I will talk about wheat flour, the most used for breads all over the world. Historically, wheat is one of the first and most important cereals to be used by ancient civilizations. It first appeared almost 10000 years BC in the area in the Near East watered by rivers Tigris and Euphrates, called the Fertile crescent. Over the centuries, wheat started to be grown in other areas such as Europe and China. Worldwide, wheat is now produced for the most part in the European Union, mostly in Italy and France.
There are different wheat flours that can be obtained, depending on which part of the kernel is used. The wheat kernel is composed of three parts. The bran: it is the outer protecting skin of the seed and is a good source of fiber and vitamin B. The endosperm: it contains carbohydrates (starch) and proteins. The germ: much smaller than the endosperm, it is where the nourishment for the seed is stocked. It's also a source of carbohydrates, along with antioxidants, vitamin E and B.
White flour as we know it, comes from the endosperm. When the germ is added to the endosperm, we have germ flour. When all three pats are grounded together, the result is Wholemeal (also called whole grain) flour. A particular kind of wholemeal flour is the so called "Graham" flour, where the three parts are treated separately and then out back together in the same proportions.
The proper flour to bake bread at home is (guess what) bread flour, or "strong" flour. The more you knead a dough made with strong flour, the more resistant (strong) and elastic it becomes. This is because kneading develops gluten, a proteic composite. Gluten prevents the molecules of carbon dioxide (produced by the action of yeast) from leaving the dough, leaving the bread with its typical holes inside once it is baked.
To know if a flour is strong enough to be used in bread making, we should look at the content of proteins: if it is below 10% then the flour is soft, over 10% (11-12%) then it suitable for bread. Other uses of strong flour are pizza, Italian focaccia or fresh Italian pasta. Soft flour is used for pastries and cakes. One exception is Irish soda bread, made with soft flour.