What do plain flour in choux pastry?

* Structure: Plain flour provides the structure for the pastry. When the flour is cooked in the boiling water and butter mixture, it gelatinizes, forming a gluten network. This network traps the steam produced by the water, creating a light and airy texture.

* Flexibility: Plain flour also gives the pastry its flexibility. This allows the choux pastry to be piped into different shapes without breaking.

* Neutral Flavor: Plain flour has a neutral flavor, allowing the other ingredients in the choux pastry, such as butter and eggs, to shine through.

Why Not Use Other Flours?

* Self-Rising Flour: The addition of baking powder in self-rising flour would cause the pastry to rise too much, creating a dense and heavy texture.

* Whole Wheat Flour: Whole wheat flour contains bran and germ, which are heavier than plain flour. This would result in a denser, more crumbly pastry.

* Gluten-Free Flour: Gluten-free flours have different properties than plain flour and may not be able to create the same airy texture.

In Summary

Plain flour is the best choice for choux pastry because it provides the necessary structure, flexibility, and neutral flavor for this classic pastry.