The Physical Nature of Flour Compression & Aeration
Wheat flour is a highly compressible powder composed of fine starch granules and protein fragments. During shipping, handling, and storage, flour settles under its own weight, driving out trapped air and compacting tightly inside its paper bag.
Because of this variable compaction, measuring flour by volume without proper preparation introduces massive weight errors. Depending on how you fill your measuring cup, a single cup of all-purpose flour can weigh anywhere from 110 grams to 160 grams—a 45 percent weight variance!
In precision baking chemistry, flour supplies the primary structural gluten proteins and gelatinized starches that absorb liquid, hold leavening gas, and set cake crumb. Adding 75 extra grams of flour to a cake recipe absorbs excess liquid, turning tender cakes into dry, rubbery sponges.