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


Air Products funded research into food freezing

Since August 2011 Air Products have a funded a collaborative research program at FRPERC to explore food freezing.

We are very grateful for the support of Air Products, a leading global supplier of food freezing and chilling systems, for their support, advice and funding. Air Products have providing access to the latest hi-tech cryogenic freezing systems, as well as advising on how to optimize systems during the research activity.

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.

Our articles on freezing

What is a frozen food? - Chris James looks at the question of what defines a frozen food.

Innovative freezing - Chris and Steve James look at the latest developments in innovative freezing technologies.

Frozen Meat - Steve and Chris James discuss the history of frozen meat.

How to specify a refrigeration system - Steve James offers advice on how to specify refrigeration systems.

Interesting links on freezing

new LinkedIn Freshline Food solutions showcase page - from Air Products

Theoretical Aspects of the Freezing Process – University of Guelph, Canada

Cryobiology – A short course – University of Calgary, US

Freezing theory – Mississippi State University, US

Examples of supercooling can be found on YouTube

Salt and the freezing point of water – Science Experiments

The freezing time of fish - Torry Advisory Note 62

Quick freezing of fish - Torry Advisory Note 27

Freezing and the cold chain