Hydration ratio controls crumb structure from dense to open
Hydration is the ratio of water to flour by weight, expressed as a percentage. At 50% hydration, a bagel dough is stiff and dense, with a tight, chewy crumb and minimal air pockets. At 65-70%, brioche and sandwich breads become softer with a finer, more uniform crumb. Beyond 80%, open-crumb breads like ciabatta and focaccia develop large, irregular holes from the wetter, stickier dough that traps more gas during fermentation.
Higher hydration requires better gluten development and longer fermentation to create the structure that can hold large gas bubbles without collapsing. The dough becomes harder to handle and more demanding technically, but the reward is dramatic: 90%+ hydration ciabatta bread has cavities that look more like Swiss cheese than bread.
Water availability shapes both chemistry and handling
Extra water means more gluten hydration, softer dough, and more time needed for fermentation (the gas production rate scales with hydration). Bakers typically increase fermentation time slightly with higher hydration to achieve the same flavor development. Dough below 55% hydration becomes difficult to work with and loses extensibility, producing compact, tough bread. Sweet doughs like challah use 65-75% hydration, a middle ground between manageability and softness.