How does a cold chain work and why must it not be interrupted?

The quality of refrigerated and frozen food as well as sensitive medicinal products is guaranteed only in the case of uninterrupted compliance with the specified temperature. This process from manufacture through storage, transport and interim storage to storage in the shop is referred to as the cold chain.

For food, continuous monitoring of the transport chain using the HACCP (hazard analysis and critical control point) concept is a mandatory requirement as an EU directive. The freezing regulation additionally defines that modes of transport (i.e. refrigerated transporters, refrigerated vehicles or even refrigerated containers) from a certain size must be fitted with a continuous temperature control system. These measure the temperature at defined intervals for one year and record the results in the HACCP temperature logs. Possible temperature fluctuations are therefore traceable at any time. Moreover, this temperature measuring technology is checked once per year for accuracy.

Despite this statutory provision, there are still a number of weak points, which cannot be resolved product specifically, efficiently and cost effectively with temperature indicators currently available on the market.


1. Storage temperature and product temperature

What is the difference between storage temperature and product temperature? The storage temperature relates to the ambient temperature prevalent in the respective cool zone, for example the temperature in the freezer lorry or in the freezer warehouse or in the chest freezer. The product temperature reflects the core temperature of the frozen product, i.e. the temperature at the centre for example of the frozen spinach, frozen vegetables, ice cream etc. For the definition of the required temperature for quality assurance of the frozen food, the product temperature is generally specified in the guidelines of the food regulation. To facilitate measuring, however, the documentation of the cold chain almost exclusively uses the storage temperature for packaged frozen food – this can be measured and recorded with thermometers or temperature sensors in the refrigeration equipment.


2. Interruption of the cold chain

In the transport of the frozen products, generally by specialist refrigerated haulage, the transhipment points are particularly critical. The frozen goods are collected from the manufacturer and generally transported to a central warehouse of the retailer. Here, the products are stored temporarily, then picked together for the individual food shops according to orders. Between storage/picking and loading, a temperature lock ensures compliance with the refrigeration temperature. After loading into the cold transport, the frozen products are delivered to the food shop. Here too, freezer rooms are available for interim storage – although these are often foregone, as the goods are sorted immediately into the freezer islands. Depending on the outside temperature, for example in summer, the product temperature can change quickly here and the cold chain is interrupted.


3. Temperature indicators on the product

To trace the possible gaps in the cold chain directly on the product, a number of temperature measuring techniques have already been developed. Temperature measuring strips or temperature stickers can be applied either directly to the transport unit (pallet, box), to the secondary packaging (carton), or directly to the product packaging. However, these indicators have several disadvantages and have therefore not become prevalent in daily use:

  • The temperature measuring strip must be activated before application (e.g. by infrared charge or manual intervention)
  • The temperature sticker is too large or too bulky for small food packages (must be stackable)
  • The temperature indicator reacts to external effects (light, hand heat etc.)
  • The temperature in the area around the label rather than the core temperature is measured
  • The unit costs of the temperature indicators are too high

Some pallets are fitted with temperature measuring strips – particularly in the case of very sensitive foods or medicinal products. However, here too, the storage or room temperature is crucial and not the product/core temperature. The innovative LOOKICE® temperature label is the first indicator that reacts to the product temperature. As soon as it deviates from the defined core temperature, this change is registered by LOOKICE®. If the deviation accumulates to a value that is critical for the product quality, then the LOOKICE label discolours. This discolouration is irreversible and can therefore not be manipulated or undone. More about this at


4. Guide values for product temperatures (refrigerated)

Food in general: +7 degrees Celsius

Poultry, game, mince, fresh meat: +4 degrees Celsius

Hens’ eggs: Unrefrigerated until the 18th day, then at +5 – +7 degrees Celsius

Frozen food: -18 – -20 degrees Celsius