Stephen J. James - Articles and news items
Issue 4 2012 • 6 September 2012 • Stephen J. James & Christian James, Food Refrigeration and Process Engineering Research Centre, Grimsby Institute of Further and Higher Education
Freezing is a well-established food preservation process that produces high quality nutritious foods that offer the advantage of a long storage life. However, freezing is not suitable for all foods and freezing does cause physical and chemical changes in many foods that are perceived as reducing the quality of the thawed material.
There is a general view that fast freezing, and the formation of small ice crystals, offers some quality advantages. However, this is not true of all foods. For example, while freezing rate may affect drip in meat there is no evidence that it has any substantial influence on its final eating quality. Nevertheless, many innovative freezing processes are currently being researched and developed across the globe to improve freezing times and product quality.
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.
Issue 2 2009 • 1 June 2010 • Christian James, Research Fellow, Food Refrigeration and Process Engineering Research Centre (FRPERC) and Stephen J. James, Director, Food Refrigeration and Process Engineering Research Centre (FRPERC)
The drive to maximise the storage and display lives of perishable foods has led to increasing interest in holding foods in the region between their freezing point and -12°C. This is a grey area in terms of much international legislation, since food is not usually considered fully ‘frozen’ until it is below -12°C and only considered ‘chilled’ above its freezing point. There is also a confusion of terms used to describe the states of foods and processes in this temperature region. The terms ‘super-chilled’, ‘deep-chilled’, ‘ultra-chilled’ or ‘partially-frozen’ are often used for foods held in this temperature region; the Japanese also use the term ‘Hyo-on’.
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