If you find yourself in a baking mood and do not have plain flour on hand, regular all-purpose flour can be used as a tried-and-true substitute. All-purpose flour is a less expensive baking staple than plain flour and is a common ingredient in both sweet and savoury recipes; it is a pantry workhorse. You can save money and space with just one container of all-purpose flour and still enjoy making cakes yourself by making some simple alterations in your recipes.
All-purpose flour and plain flour both contain wheat, which in turn contains starch and protein. Starch is a complex carbohydrate made from glucose. Protein, which creates gluten, is the most important ingredient in flour when it comes to the form and texture of baked goods. Another similarity between the two types of flour is that plain flour and some kinds of all-purpose flour are bleached. While there are unbleached all-purpose flours, there are no unbleached cake flours.
Type of wheat -- hard versus soft -- differentiates the two types of flour. Hard wheat contains a much higher amount of protein than soft wheat. All-purpose flour contains varying blends of hard and soft wheat, while plain flour contains soft wheat only. The higher percentage of protein in all-purpose flour, about 9 to 12 per cent, relative to plain flour, which is about 5 to 8 per cent, means that baked goods made from plain flour will have less gluten and will be more delicate with a more tender crumb.
You can use all-purpose flour in recipes that call for plain flour with one of two simple alterations. The first is to lower the protein amount in any brand of all-purpose flour by substituting 94 g (3/4 cup) of sifted all-purpose flour plus 2 tbsp of cornflour for every sifted cup of plain flour. The second alteration is to use a brand of bleached all-purpose flour instead of the unbleached variety. Bleached flour contains less protein, some brands have a protein content of around 8 per cent, which is comparable to plain flour.
All-purpose flour made entirely of soft wheat, like plain flour, is available in some areas. When using soft wheat all-purpose flour as an alternative to regular all-purpose flour, you'll need to add an additional 2 tbsp of flour to every 125 g (1 cup) of flour in the recipe.