According to the ServSafe Manager guidelines and the FDA Food Code, any food-contact surface that is in constant, frequent use must be cleaned and sanitized at a minimum interval of every four hours. This "four-hour rule" is based on the biological reality of bacterial growth. Under ideal conditions—moist environments with plenty of nutrients, like the milk and sugar residue found in a milkshake mixer—pathogenic bacteria can multiply to dangerous levels within this timeframe. By mandating a complete cleaning and sanitizing cycle every four hours, the operation effectively breaks the bacterial growth cycle before it reaches a "log phase" where the population explodes.

For a milkshake mixer, the process involves more than just a surface wipe. The equipment must be disassembled if necessary, washed with detergent in hot water, rinsed to remove soap film, and then treated with a chemical sanitizer (such as chlorine or quaternary ammonium) for the required contact time. If the environment is particularly warm—exceeding $70^{\circ}F$ ($21^{\circ}C$)—the risk of bacterial growth increases, but the four-hour standard remains the regulatory baseline for room-temperature operations. Managers are responsible for implementing this into the daily workflow, often using "timed" cleaning logs to verify compliance. Failure to sanitize frequently used equipment is a common critical violation during health inspections because it creates a direct path for cross-contamination. If the mixer is only used occasionally, it must still be cleaned and sanitized after each use or before switching to a different flavor that might contain allergens. This rigid schedule is a core component of Active Managerial Control, ensuring that the physical environment remains safe despite the high volume of food production.