PRIMARY VENTS: Negative quality changes begin with a primary event (degradation mechanism), which causes a change in the attribute—e.g., transmission of light, gas, moisture, mechanical stress, etc.—after which qualitative decay occurs: sensory quality, microbial contamination, loss of nutrients or pigments, production of unwanted compounds, physical changes. 3 Then the minimum quality level is quantified, 4 quality indicators are evaluated, 5 and how and when the critical level is reached.