When the power goes, the clock starts on everything in the cold room. Once the unit stops, the room carries its cold for a while on its insulation and the mass of goods inside; a full room lasts longer than an empty one.
Keep the door closed
Every opening shortens that time, because warm humid air settles between the shelves. The FDA gives this order of magnitude for household appliances: an unopened refrigerator keeps food cold for about 4 hours, a full freezer for about 48 hours (24 hours if half full). In a cold room the time depends on loading and insulation; an external thermometer and an alarm let you monitor without opening the door.
Cold that does not depend on the grid
A eutectic plate frozen in advance cools the inside of an insulated container independently of the mains. The GEBHARDT Isotec TBX holds the cold chain for up to 24 hours with eutectic plates or dry ice; plates come with melting points of -3, -14, -18 and -21 °C, so fresh and frozen goods get different plates.
This is not something to buy on the day of the cut: the plate has to be frozen beforehand, on racks that leave an air gap between plates, at least 5 °C below its melting point. If a full set of plates always sits on the rack, a power cut is an incident.
After the cut
When the power returns the question is what the core temperature of the load was and how long it stayed there; the measurement is taken in the middle of the load, not in the air. The FDA says perishable food that stayed above refrigerator temperature (40 °F, about 4.4 °C) for 4 hours or more is discarded.
Before the next cut, write half a page and pin it behind the cold room door:
- Where the full plates are kept
- Which plate goes into which container
- Which goods move first
- Who measures and where the result is recorded
