Baking
Practical Action
centre of the food; 2) the temperature of the oven; and 3) the speed that air moves in the baking
chamber. Heating is by a combination of infrared energy that is radiated from heaters and oven
walls; by conduction from the hearth through the baking pan or tray; and from circulating hot air.
The hotter the oven, the more energy is radiated from the walls and conducted from the hearth, and
so produces faster baking or roasting. The faster the air moves in the oven the quicker the food is
heated. This is because foods are surrounded by a film of stationary air, which forms a barrier to heat
moving into the food. The thickness of this ‘boundary layer’ depends on the speed of the air in the
chamber. Fans that reduce its thickness increase the rate of heating and commercially produced
ovens may be ‘fan-assisted’ to increase the rate of baking. Fans also distribute air uniformly through
the baking chamber so that there are no hot- or cold-spots, and the same rate of baking is achieved
in all parts of the oven.
A common design of small-scale gas or electric oven is the ‘deck’ oven, which has an insulated steel
chamber fitted with a fan and a full-width door. The temperature is controlled automatically by either
adjusting the flow of gas to burners at the base of the chamber or using a thermostat in electric
ovens. Electric ovens should be fully earthed to prevent the risk of electrocution, and wiring should
be located and insulated so that it is not affected by heat from the oven. Electric ovens may have
microprocessor controls that are programmed to allow operators to select a code for each product
without the need to remember the baking conditions. Microprocessors then automatically control the
temperature and humidity in the baking chamber and the baking time. Multi-deck ovens (Figure 7)
have 4-16 chambers stacked vertically. Each baking chamber has separate controls so that they can
be simultaneously used for different products. The ‘modular’ construction allows production to be
expanded by adding another deck without having to replace the entire oven. These ovens are usually
fan-assisted and are fitted with steam mist injectors to produce a glazed crust on products. They are
available in different sizes, with low or high crowns, and are widely used by small- and medium-sized
bakeries, food service outlets, and in-store bakeries at larger supermarkets in some countries.
Figure 7: Multi-deck oven, (courtesy of Picard Ovens Inc. at www.picard.com)
Rack ovens have a single large baking chamber with a full-height door. A mobile rack of trays
containing the products is wheeled into the oven and remains stationery during baking. At higher
levels of investment, the ‘rotary hearth’ oven is similar to the rack oven but the rack of trays rotates
inside the baking chamber. The ‘reel’ oven has a steel chamber and hinged trays fitted between
slowly rotating wheels inside. As the wheels turn, the trays of food move vertically through the oven
and also horizontally from front to back. They are loaded and unloaded as they pass the door. The
movement through these ovens ensures that the products are baked uniformly. They have a high
capacity and are suitable for larger-scale bakeries.
Fuels
The local cost and availability of fuels and electricity are one of the main considerations when
selecting an oven, and they are also the largest operating cost for bakery businesses. Mains gas or
bottled gas (propane or butane Liquid Petroleum Gas (LPG)) are the preferred options in countries
that have an established gas distribution system and if the price is sufficiently low. This is because
they burn cleanly and produce few odours that could contaminate products. In places that do not
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