Deterioration is the fact of becoming worse — the gradual decline in quality, safety, or nutritional value that all foods undergo from the moment of harvest or manufacture. It runs through several channels at once: microbial growth, enzyme activity, oxidation of fats, moisture migration, and staling all push the product downhill. The rate depends on the food’s composition and its environment — temperature, humidity, light, and oxygen exposure. Food science exists largely to measure, predict, and slow deterioration: shelf-life testing maps the decline, packaging interrupts it, and preservation methods from refrigeration to preservatives hold it off. Quality systems define the point where deterioration crosses from acceptable change into spoilage or hazard. Understanding deterioration is understanding that food is never static — it is always travelling, and the technologist’s job is to manage the journey.