Transportation
Transportation
Friday, 10 April 2009
Early transportation studies at the MRI focused on the problems of poor temperature control during road transportation of both chilled (Cutting & Malton, 1972a, b; 1973) and frozen meat (Malton, 1974).
In our 1970-71 survey of vehicles used to transfer chilled meat from small abattoirs to shop, almost 70% were unrefrigerated and 20% had no insulation (Cutting & Malton, 1972). Eight of the mechanically refrigerated vehicles had propane-driven R12 compressors, and one used diesel. They could be mains-operated when static. The uninsulated vehicles were mostly 10 cwt delivery vans, with no partition between driver and load. Meat temperatures when delivered ranged from 8 to 10°C in refrigerated, and 9 to 14°C in unrefrigerated, vehicles.
Frozen meat temperatures after transportation in refrigerated trailers in the early 1970s were much higher than desirable. Temperatures of carcasses in the centre of loads averaged -7.2°C while those measured at the top of the load ranged from -5.1 to -4°C.
During the 1970-80s Dick Malton carried out extensive transport trials with meat companies. The increased availability of portable temperature recorders provided critical data on meat and air temperatures during loading and transportation. Such trials were not always successful, one recorder being returned in pieces after subjected to a controlled explosion by the bomb squad! However, the investigations clearly identified the main causes of poor temperature control during transportation (Malton, 1979). These were: loading with warm product; heat infiltration during loading and poor air distribution around the product. Beef carcasses had deep temperatures of up to 20°C on loading (Winstanley, 1986) whilst, in one case, cooked pork pies had an internal temperature of 27°C after a 4.5 h journey (Winstanley, 1981). Boxes of meat stacked in contact with the walls of a vehicle increased in temperature by 8°C during a 24 h journey (Winstanley, 1981).
Some of the most interesting data gathered by Dick Malton unfortunately wasn’t published. For example an unpublished MRI Industrial Development Group study by Malton (1985a) looked at the temperatures of lamb carcasses during transport from one UK abattoir to France. The abattoir in question had an agreement with the inspectors that lamb carcasses could be loaded at 12-15°C (deep hind) provided that the vehicle remained at the abattoir until the temperature was lowered to below 7°C, this check was done after about 6 h. Although three of the 5 carcasses measured were loaded above 9°C at 16:20 they were cooled to below 7°C at the time of inspection at 22:00 and further cooled during the 9.5 h journey to below 3°C. The carcass loaded at 17.6°C was at the back of the load and exposed to the refrigerated airflow so cooled to 8.4°C at the time of inspection and to 2.0°C at unloading.
The problems, and the means of overcoming them, were conveyed to the industry via a series of conferences and popular publications throughout the 1980s by Monica Winstanley (1981a, b, 1982, 1986). Since that time the growing demand from legislation and retailers for lower delivery temperatures, has put increasing pressure on fleet operators to improve temperature control. However, there are substantial difficulties in maintaining the temperature of chilled foods transported in small refrigerated vehicles that conduct multi-drop deliveries to retail stores and caterers. The vehicles have to carry a wide range of products and operate under diverse ambient conditions. During any one delivery run, the chilled product can be subjected to as many as fifty door openings, where there is heat ingress directly from outside air and from personnel entering to select and remove product. The design of the refrigeration system has to allow for extensive variation in load distribution, which is a function of different delivery rounds, days of the week and the removal of product during a delivery run. A refrigeration system’s ability to respond to sudden demands for increased refrigeration is often restricted by the power available from the vehicle. All these problems combine to produce a complex interactive system.
In the 1990s a MAFF LINK programme, a joint UK Government/industry funding scheme, provided the funding to tackle these complex interactions. A predictive program was developed from individual modules that were verified either using a static vehicle body in our processing halls or on the road (Parry-Jones & James, 1994). The resulting program, called ‘CoolVan’ (Figure 20), is a unique tool for vehicle operators and manufacturers (Gigiel, 1997; 1998; Gigiel & James, 1998). Much effort was put into making the program very user friendly and easy to use resulting in very favourable feedback from the many companies involved in the LINK. The program was released subsequently as a commercial product. The verification work on this project highlighted many of the practical problems of multi-drop local delivery, and the means of overcoming them, and much of this data has been conveyed to the industry via a series of conferences and popular publications (James & James, 2002). A comprehensive review of modelling food transport systems by FRPERC has been recently published in the International Journal of Refrigeration (James, James & Evans, 2006).