It was mentioned in Chapter 1 that food quality is a dynamic state continuously moving to reduced levels over time after production (see Figure 1.2 in Chapter 1). By selecting a proper quality indicator, namely, the critical descriptor, food quality decay can be monitored as a function of storage time. For instance, quality decay can be described by monitoring the loss of a peculiar food property or a target nutrient or by measuring the development of undesired changes such as those regarding food color and appearance, oxidation status, microbial load, and so on. Figure 2.1 shows some examples of possible evolutions of a generic quality indicator I over time.