Walk-in temperature
log.

Measure product temperature, not air. Keep a probe thermometer in a container of water on a middle shelf and read that. The door display reads air, which swings with every defrost cycle and every delivery; the water reads like the food does, and it is the number a health inspector trusts.

The target range is 35–38°F. That keeps every shelf under the 41°F FDA cold-holding line with margin for door openings and defrost. Log twice a day, once in the morning before deliveries and once during the afternoon.

When a reading is over 41°F: check the door and gaskets, note the corrective action in the log, and re-check within the hour. Chilled food above 41°F for more than a limited window, commonly around four hours, has to be discarded. The full background is in how cold a walk-in should be.

Watch for drift, not just bad readings. A log that creeps from 36 to 38 over three weeks is telling you something even though every reading passed. Slower recovery and a rising average are how faults look before they are failures; what one costs is in the walk-in failure cost calculator.