During which step do mechanical dishwashers utilize detergent's wetting action to break down food?

The correct answer is the wash step, as this is when mechanical dishwashers use detergent's wetting action to effectively break down food residues. During this phase, the main function of the detergent is to lower the surface tension of water, allowing it to penetrate and cling to food particles. This increased wetting action facilitates the removal of grease and grime from dishes and utensils, ensuring they are thoroughly cleaned.

In the wash step, the detergent works in combination with heated water to optimize its effectiveness. As the water is sprayed onto the dishes, the wetting action helps to dislodge and emulsify fats and oils, contributing to a thorough cleaning process.

The other steps, while essential for the overall dishwasher operation, do not involve the active cleaning action provided by detergent. The prewash may help to remove large food particles before the main wash but does not utilize the detergent in the same manner. The rinse step is designed to remove detergent and any remaining food particles, while the air dry phase focuses on drying the cleaned dishes rather than cleaning them. Therefore, the wash is the critical step where the detergent plays its pivotal role in breaking down food residues.