All the latest news on current and past research into food freezing from the Food Refrigeration & Process Engineering Research Centre (FRPERC).

Freezing is a long established food preservation process that produces high quality nutritious foods with a long storage life. In general, the term freezing refers to the process in which the temperature of the food is reduced to a temperature below its freezing point, while the term frozen is used to describe the subsequent state the food is kept in, i.e. the maintenance of the food below that temperature during the rest of the cold-chain. The formation of ice crystals during freezing and frozen storage causes physical changes to the structure of foods. In most cases, these changes are perceived as reducing the quality of the thawed material.  In extreme cases, such as cucumbers or salad vegetables, freezing completely destroys the structure of the food.  In meat and fish, the main result is increased drip on thawing.

Current developed food freezing technologies encompass air blast, contact/plate, immersion and spray freezing systems.  Although often considered a separate technology cryogenics can be considered to be a sub field of blast, immersion or spray, depending on how the cryogen is used and the method of application.  Hybrid systems such as cryomechanical also exist. Cryomechanical systems initially crust freeze the product using cryogens before completing the freezing process with a conventional mechanical air blast or belt freezer.  Most of these technologies have been with us since the 1960s and although there have been improvements these technologies have essentially remained the same since then.

Many innovative technologies being researched and developed currently promise improvements in the quality of frozen foods. Some innovative freezing processes (impingement and hydro-fluidisation) are essentially improvements of existing methods (air blast and immersion, respectively) that by providing far higher surface heat transfer rates than previous systems aim to improve product quality through rapid freezing. In these cases, the advantages may depend on the size of the product, since the poor thermal conductivity of many foods limits the rate of cooling in large objects rather than the heat transfer between the cooling medium and the product. Other processes (pressure shift, magnetic resonance, electrostatic, microwave, radio frequency, and ultrasound) are adjuncts to existing freeing systems (such as air blast, immersion, cryogenic etc) that aim to improve product quality through controlling the way that ice is formed in the food during freezing. An alternative is to change the properties of the food itself to control how ice is formed during freezing (such as in dehydrofreezing and the use of antifreeze and ice-nucleation proteins).

Find out more about freezing in our publications, articles and links below.  A full list of our publications on cold chain topics can be found here. For more about our past work on this topic please read our research review on freezing.