Bread flour and all-purpose flour differ mainly in gluten content: bread flour has more of it. For occasional bread bakers, keeping a large bag of bread flour on hand can be inconvenient, but a product known as a gluten additive or gluten flour offers a workaround. Adding about one tablespoon of the additive to each cup of all-purpose flour turns it into bread flour, according to the source material.
The trade-off is cabinet space. A single container of gluten additive can replace a separate bag of bread flour for bakers who only make bread occasionally, while still delivering the higher gluten level that bread recipes call for.
The source does not specify brands, exact ratios beyond one tablespoon per cup, or whether the substitution works identically across all recipes. It also does not address how the additive affects texture, rise, or flavor compared with store-bought bread flour. Those details would require testing or guidance from a reliable baking authority.
Editorial Notes