Freezer burn is surface dehydration. Moisture sublimates out of the fruit, migrates through the pack and refreezes as frost on the inside of the liner, leaving pale, dry, leathery patches on the berry. The two causes are a poor moisture barrier around the product and temperature fluctuation during storage or transport.
Why fluctuation is the main driver
Every rise in temperature increases the vapour pressure difference between the fruit surface and the surrounding air, driving more moisture out. When the temperature falls again, that moisture deposits as frost somewhere other than the fruit. The fruit never gets it back. A pack that has been through many small cycles shows more frost and more surface damage than one held steadily, even at the same average temperature.
Preventing it
- Seal the liner properly; an open twist is the most common defect in practice.
- Use a liner thickness and material appropriate to the shelf life you claim.
- Hold storage temperature steady rather than merely low. Steady beats cold-on-average.
- Limit dock dwell and door-open time at every handover.
- Consider glazing for high-value fruit, and agree whether the declared weight is net of glaze.
Frost inside the liner is also diagnostic evidence in a temperature dispute – see cold chain management.