It is still true to say that a baker has very little interest in a baking oven's particular features unless it is first established that it can produce the quality of products required. Technical features, years of research, and the latest marketing techniques will not even begin to make an impression until this most important question has been answered to the baker's satisfaction.
However, suppliers of in-process oven systems have recognised that increasing pressure on food technologists provides them with an opportunity to ease the workload, while improving the operator's ability to control cooking programs.
"There are so many variables that have to be considered and validated," says Steve Offley, food product manager with monitoring system specialist Datapaq. "These include largest portion size, coldest pre-cook temperature, shortest cook time, coldest location in the oven, highest oven loading, and shelf temperature variations.
"Probe placement is critical to the quality of the data collected pushing a needle probe through a fillet into the conveyor mesh will not provide accurate data on the core cook temperature," he says.
Recent developments have led to the introduction of a food tray which allows products to be probed accurately away from the conveyor without the need to disrupt production. Product positioning in the oven is guaranteed with fixed probe positions, and probe movement in the product is eliminated.
Many processors rely on achieving a minimum core temperature; others, on time at temperature. "Both of these approaches are workable although they can result in over-cook at the expense of product quality, says Offley. For this reason Datapaq has collaborated with Campden and Chorleywood Food Research Association (CCFRA) to determine safety levels for Listeria monocytogenes. "The parameters, which resulted from the research, have been used in software used to calculate and control the micro-organism population," he says.
Measured time-temperature profiles are often used in thermal process validation work to prove that the number of micro-organisms within a product has been reduced to a safe level. However, implementing process temperature monitoring systems provides much more than simply satisfying hazard analysis critical control point (HACCP) requirements, says Offley.
"The competitive nature of processing and the drive to increase productivity and yields means that the maximum amount of information and data must be obtained," he says. "Profiling provides this without compromising safety.
Time temperature indicators
CCFRA, with the support of a number of manufacturers, is itself involved with work on time temperature integrators (TTI). The work, as described by CCFRA's Gary Tucker, is mainly aimed at determining the commercial sterility and quality of thermally processed food in processes in which the trajectory of the food or particulates cannot be measured using existing techniques.
"We aim to continue to investigate processes in which the target food moves while it is being processed," says Tucker. "The advantages of the method are that the TTI will stay in position within the food and that it has no trailing wires to interfere with the measurements."
"TTI relies on accurate methods of measuring food temperatures that do not interfere with the temperature response itself," he says. This can be difficult, he adds, especially with products cooked in continuous systems (poultry, nuggets, burgers, bread) and products with discrete pieces (preserves, soups, ready meals, dressings).
However, CCFRA has shown that TTIs offer an economic method of thermal process analysis, compared to temperature-based and microbiological-based methods, and can be used in industrial processes which cannot be validated using a temperature-based approach.
Other TTI-based research is being undertaken by CCFRA alongside investigations into the proving and baking of bread and biscuits. One study into heat recovery, for example, aims to make improvements to tubular heat exchangers. Although heat recovery has been relatively low on the list of priorities, because of the low cost of energy compared with that of raw materials, says Tucker, as fuel prices have risen, more attention is now being paid to energy conservation.
"Better design and better operation of heat exchangers could mean that they can be operated in heat recovery mode with a wider range of food products than presently is the case," he says. "Areas have been identified that could be redesigned for example, stagnation areas and tube supports."
Oven videoing
Although the Food Chain Centre of Industrial Collaboration (CIC) at the University of Leeds is mainly concerned with research into food, it has recently become involved in the development of a low-profile oven video acquisition system.
"Our organisation was set up in July 2004 by the Yorkshire Forward Regional Development Agency, funded by central government," says Graham Clayton. "The OvenScope a self-contained, battery-powered, PC-based recording system for monitoring the inside surfaces of ovens used in the continuous manufacture of baked products was developed by other laboratories. However, research continues and the product has now been enhanced as a result of work carried out by CIC."
Camera systems and digital recording equipment pass through cool ovens gathering images of the upper and side faces along with a forward view as the conveyor advances. Subsequent computer-aided analysis of the images allows oven damage to be located and repaired quickly and efficiently thus minimising costly operational stoppages.
European Process Plant (EPP), along with the manufacturers which supply its equipment, has been engaged in research and development into the distribution and control of heat to baking ovens. Using a thermal oil system which is based on a central supply unit, a heating boiler can distribute heated oil to a number of baking positions.
"From the oil circulating, the baking ovens draw exactly the amount of energy they require, as determined by the control system," explains EPP's Keith Stalker. "The heater plates inside the oven are then supplied with thermal oil through a separate, secondary circuit. As a result, smooth heat radiates onto the products from above and below."
With the thermal oil heating system several multi-deck baking ovens can be served and controlled by just one central heating boiler. "This offers the advantages of only one boiler and one flue being required for the operation of several units," he says. And it is possible to combine several central heating boilers and form a battery to serve an even wider system.
Currently, boilers and ovens heated by thermal oil are designed for use at temperatures in excess of 300°C. However, further developments, such as equipping the oven with a magnetic coupling pump to eliminate rotating seals, are also in hand.
Convection ovens for baking
Another baking system gaining attention is a convection oven which offers dependable and stable airflow within the baking chamber.
APV Baker's Keith Graham describes three types that have been developed: direct convection, which offers fast bake times; indirect convection, which gives a wider choice of fuel types and improved levels of control; and a direct recirculating version with combined radiant and convection heating. "Bakers can choose increased output from a conventional footprint or a shorter oven that offers floor space savings," says Graham.
The airflow innovation is described as "a major step in the progress of baking from a 'black art', relying largely on operator experience, to a scientific process", claims Graham. In convection ovens it is a simple matter to obtain a uniform flow of hot air on to the product, he adds. "However, it has not been possible to obtain an unvarying airflow away from the product and, as a result, heat transfer into the product was subject to fluctuation."
In the new oven, air circulating above and below the product and the conveyor band, is returned to the fan before recirculation. This overcomes the problem caused in traditional convection ovens which have a single circulation fan inlet that creates uneven heating as air is forced around the edges of products.
APV Baker has also developed a new heat exchanger designed to optimise the heat rate across it. "This feature improves efficiency and extends the service life by avoiding hot spots and thermal stresses," claims Graham.
KEY CONTACTS
APV Baker 01733 283000CCFRA 01386 842000Datapaq 01223 423141EPP 01372 745558Food Chain CIC 0113 3437593