Retention of moisture is the ability of a food or ingredient to hold on to its water content instead of losing it to evaporation. It matters wherever drying out ruins quality: bread stales as moisture migrates from crumb to crust and then to the air, cooked meats shrink and toughen as juices escape, and fresh produce wilts. Food technologists manage moisture retention with humectants such as glycerol and sorbitol, with hydrocolloids that bind water, with packaging that blocks vapour transmission, and with storage at high relative humidity. Measuring it, usually as weight loss over time under controlled conditions, predicts shelf life and eating quality. In baking, good moisture retention is the difference between a soft crumb on day three and a brick.