Not a cold box. A documented chain of custody for temperature.
Anyone can rent a refrigerated trailer. The product is the proof — that the set-point held from your dock to theirs.
A reefer holds temperature. It does not chill warm freight down. Everything in cold-chain discipline — pre-cool, pulp temp, continuous mode — follows from that one fact.
Temperature-controlled (reefer) freight is cargo transported in a refrigerated trailer that holds a specified set-point temperature — anywhere from −20°F deep frozen to 70°F climate-controlled ambient— for the entire journey, with the temperature continuously recorded as proof. The refrigeration unit (“reefer unit,” almost always a diesel-powered Carrier or Thermo Kingmounted on the trailer’s nose) both cools and heats, which is why the same equipment protects ice cream through Phoenix in July and chocolate through Winnipeg in January.
The unit’s operating mode matters more than most shippers realize. In start/stop (cycle-sentry) mode the engine shuts off at set-point and restarts when the box drifts — it saves fuel, but air temperature swings several degrees between cycles. In continuous modethe unit runs non-stop, holding the box inside a degree or two and keeping air moving through the load. Frozen goods, produce, floral and all pharma ride continuous; the fuel difference is trivial next to one rejected load. Specifying the mode is part of a competent reefer quote — and it’s printed on ours.
Frozen, chilled, or climate-controlled — what reefer covers
Reefer is not one temperature; it’s a 90-degree spectrum. Deep frozen (−20°F) for ice cream and frozen seafood. Frozen(−10 to 0°F) for meat, vegetables and bakery. Chilled(32–39°F) — the busiest band on the road — for produce, dairy, deli and fresh protein. Cool(40–55°F) for floral and select pharma. And climate-controlled ambient(up to 70°F) for chocolate, cosmetics, wine and electronics that simply must not freeze or bake. Pharma adds its own bands on top: 2–8°C for biologics and vaccines, −20°Cfor frozen drug product, and 59–77°F controlled room temperature. One mode, many disciplines — the spectrum below maps all of them.
Why air temperature isn’t enough (pulp temp)
The return-air sensor on a reefer unit measures the aircoming back off the load — and air lies. Load 26 pallets of warm product into a perfectly pre-cooled trailer and the air can read 36°F within minutes, while the product core sits at 50°F and stays there, because a trailer unit can’t extract field heat from 40,000 lb of cargo in transit. Pulp temperature— a calibrated probe inserted into the product itself — is the only number that describes the freight rather than its atmosphere. Qeep drivers verify pulp temp at loading and record it on the BOL, and re-verify at delivery when your SOP requires it. It’s the difference between proving the cold chain held and arguing about it.
What FSMA requires of a refrigerated carrier
Since the FSMA Sanitary Transportation of Human and Animal Food Rule (21 CFR Part 1, Subpart O) took effect, temperature control for food in transit has been a legal obligation, not a best practice. At a high level the rule requires shippers and carriers to agree — in writing — on temperature and sanitation requirements; to verify the trailer is pre-cooled and clean before loading; to demonstrate the temperature was controlled throughout transit; to train personnel; and to maintain records. In other words: federal law now expects exactly the documentation discipline a good cold-chain broker was already enforcing. “Refrigerated” is really a documented chain of custody of temperature — the trailer is just the instrument.
