|technology > heating, cooling > baking|
heating it with hot air. A secondary objective of baking is to preserve the food, by destruction of the microorganisms and reduction in the water activity at the surface of the food. However, the shelf-life of most baked foods is limited, unless products are refrigerated or packaged.
|Field of application|
|Techniques, methods and equipment|
|a) Direct-heating ovens|
|b) Indirect-heating ovens|
|c) Infrared oven for baking of vegetables|
filling or as a topping component in many food products such as pies, pizza and snack foods. It is a common problem with filled food products that the moisture content of the filling component (commonly fresh vegetables) adversely affects the casing or base component of the food product during storage, via moisture migration into the casing or base. The alternative of conventional dehydrated vegetables is not suitable, since those have undesirable taste and texture properties and require rehydration prior to use. Baked vegetables do not have these drawbacks. Suitable vegetables according to this process include zucchini, peppers, mushrooms, potatoes, cauliflowers, onions, artichokes and aubergines.
air (110 – 240°C) or infrared irradiation. The moisture at the surface is evaporated and removed by the circulating air. When the rate of moisture loss at the surface exceeds the rate of transport of moisture from the interior of the product to the surface, the surface dries out and a crust is formed. Ovens, using hot air as the heat transfer medium, are classified as direct or indirect heating types. For baking of fruits and vegetables infrared ovens are used. All oven types can be batch or continuous in operation.
temperature in the oven is controlled by adjusting the air and fuel flowrates to the burner. The fuels normally used are natural gas, propane and butane. The gas is burned in ribbon burners above, and sometimes below, the conveyor belt and product. The advantages of direct heating ovens are: short baking times, high thermal efficiencies, rapid start-up and good temperature control. Good management and care is necessary to prevent contamination of the food by undesirable products of combustion.
wall, whilst exhausting the combustion gases from the top of the oven. Electric ovens are heated by induction, heating radiator plates or bars. In batch ovens, the walls and the base are heated. In continuous ovens, radiators are located above, alongside and below the conveyor belt. Batch ovens incur higher labour costs than continuous ovens. Another drawback can be the nonuniformity in baking times, caused by the delay in loading and unloading the oven.
- flash blanching vegetables in up to 100% saturated steam
- steam cooking vegetables in 35 to 65% saturated steam
- baking vegetables by exposure to infrared radiation.
The vegetable pieces are then flash blanched for 60-80 seconds, in 100% saturated steam in a jet stream oven at 200-300°C. The steam is delivered to the oven at a rate of approximately 500 to 540 kg/h. The air speed in the oven is 17-25 m/s. The product is next transferred into a second jet stream where it is steam cooked at 270–300°C in 50% saturated steam for 65-85 seconds (same conditions as in the previous step for steam and air speed). The product is then transferred to an oven for infrared baking for 3.5–5 minutes. The air temperature in the oven increases from 240°C to 350°C as the product travels through the oven on a conveyor belt. In this process, the vegetables lose approximately 30 to 60% of their water content, depending on the vegetable.