Physics and Chemistry of Pastry

The striking differences in texture between various kinds of pastry have simple causes which lie in the nature of wheat flour and certain kinds of fat. Wheat flour, when kneaded into a plain dough made with water, develops strands of gluten, which are what give an elastic, tough quality to bread. In ordinary pastry, such a texture is undesirable; so a fat or oil is added. This retards the development of the gluten, mainly by physically interposing itself between the grains of flour so that the strands cannot tangle and be drawn out. A hard, solid fat such as lard or suet is most effective here. Lard in particular has a coarse, crystalline structure which makes a highly effective barrier. Butter is less effective, and shortcrust pastry made with butter alone has an inferior texture. If the fat is melted with hot water, or if liquid oil is used, the thin oily layer between the grains offers less obstacle to gluten formation and the resulting pastry is tougher. This is the effect deliberately sought in hot water pastry.