Baking and Roasting and Frying
15 likes9,389 views
Baking and roasting are similar processes that use heated air to alter the quality of foods. Baking is typically used for flour-based foods and fruits, while roasting is for meats, nuts and vegetables. Both processes involve heat transfer through radiation, convection and conduction to cook foods internally without exceeding 100°C. This causes surface changes that improve qualities like moisture retention. Ovens can be direct or indirect heating types, and batch, continuous or semi-continuous systems. Frying methods include deep frying by full submersion in hot oil, shallow frying with partial submersion, and stir frying using minimal oil. Frying oils undergo hydrolysis and oxidation over time, producing compounds that degrade quality
Baking and Roasting and Frying
- 1. 1 Y.Bavaneethan. Lecturer Department of Food Technology SLGTI. 1/5/2018 Y.BAVANEETHAN
- 2. Baking and Roasting Baking and roasting are essentially the same unit operation. Both use heated air to alter the eating quality of foods. Baking is usually applied to flour-based foods or fruits, • And roasting to meats, nuts and vegetables. Purpose of baking is; • Preservation by destruction of micro-organisms and reduction of the water activity. Shelf life of most baked foods is short • Extended by refrigeration or packaging. 1/5/2018 2Y.BAVANEETHAN
- 3. In an oven, heat is supplied to the surface of the food; • by a combination of infrared radiation from the oven walls. • by convection from circulating air • by conduction through the pan or tray. Baking takes place at; • Atmospheric pressure and moisture escapes freely from the food, • The internal temperature of the food does not exceed 100ºC. More rapid heating and higher temperatures used in baking; • Cause complex changes to the components of the food at the surface. (110–240ºC and a crust ) • These changes effect the eating qualities and retain moisture in the bulk of the food.1/5/2018 3Y.BAVANEETHAN
- 5. Equipment • Ovens are classified into direct or indirect heating types 1. Direct heating ovens • Directly heated ovens, air and products of combustion are recirculated by natural convection or by fans. • The temperature in the oven is controlled automatically, by adjustment of air and fuel flow rates • Natural gas is commonly used • But propane, butane, fuel oil or solid fuels are also used. • If abnormal baking condition, the pressure-relief panels are fitted to the top of the ovens to protect. 1/5/2018 5Y.BAVANEETHAN
- 6. The advantages of direct heating ovens include: • Short baking times • High thermal efficiencies • Good control over baking conditions (using the fan speed and the rate of fuel consumption) • rapid start-up, as it is only necessary to heat the air in the oven. 02. In- direct heating ovens • Steam tubes are heated by burning fuel or remote boiler. • Heated air is commonly recirculated through the baking chamber and through a separate heat exchanger. 03. Batch ovens 04. Continuous and semi-continuous ovens1/5/2018 6Y.BAVANEETHAN
- 10. Deep frying Involves the immersion of food in a pan of hot fat. Deep fried foods are high in Fat but; • Less fat is absorbed if the oil is very hot when the food is put into it. Food that are deep fried ,should be coated to prevent overcooking and; • prevent the food breaking up and absorbing too much fat. When the food is placed in the hot fat; • Eg: the egg in the coating coagulates rapidly and thus forms a protective layer around the food. • The food inside continues to cook by conduction and retains its flavour and texture. Deep fat fryers are safer because they control the oil temperature. . 1/5/2018 10Y.BAVANEETHAN
- 11. Shallow frying Involves the cooking of food in layer of hot fat that comes half way up the food. Heat is conducted from the base of the pan to one surface of the food at a time. • This means the food has to be turned at regular intervals to ensure even cooking. Food that is shallow fried does not necessarily have to be coated. Dry frying Some foods e.g. bacon and sausages can be fried without the addition of fat as • They contain sufficient fat to prevent sticking to the pan. Non stick pans are most suitable for this form of frying 1/5/2018 11Y.BAVANEETHAN
- 12. Stir Frying • All ingredients should be finely chopped. into small pieces so that it cooks quickly. • A teaspoon of oil is heated in the pan and the food is put in and stirred continuously to ensure even cooking. • Few nutrients are lost and the food remains crisp and well flavoured. • It is a quick and healthy method of cooking. 1/5/2018 12Y.BAVANEETHAN
- 13. Product flavor Product texture Product appearance Mouthfeel Shelf life of the product Availability of the oil Nutritional requirements Any selection of frying oil must be Low in saturated fat Low in linolenic acid High oxidative and flavor stability Not hydrogenated (trans-fat free) 1/5/2018 13Y.BAVANEETHAN
- 14. In Food Loss of moisture Development of dark color, firm texture and fried flavor In Oil Bland flavor at initial frying Changes due to chemical reactions Dark and viscous Unsaturated fatty acids decreases with increasing number or time of frying Oil and food both undergo severe changes due to frying, => different frying process, variables of oil, food and process conditions. Understanding new compounds in different oils and their reactions and functions are important study during the frying process.1/5/2018 14Y.BAVANEETHAN
- 15. • New compounds formed in oils during frying process • Frying is a complex process to understand completely and thoroughly. Causative agent Change effect New compounds Moisture Hydrolysis Free fatty acids Diaclyglycerol Monoaclyglycerol Air and Metals Oxidation Oxidized monomers Oxidized dimers & polymers Volatile compounds (aldehydes, ketones, hydrocarbons) Sterol oxides High temperature Polymerization Dimers and non-polar polymers Cyclic monomers Trans isomers and position isomers 1/5/2018 15Y.BAVANEETHAN
- 16. Hydrolysis in fats and oil due to lipolytic enzymes or moisture In Frying High moisture in foods to be fried Hydrolysis end products • TAG + H2O Free fatty acids (FFAs) + di or monoacylglycerol More in oil with short-chain unsaturated fatty acids than long chain saturated fatty acids FFAs - Off flavors and decreases smoke point of the oil • Di- and monogylcerides - Foaming of oil • Frequent replacement of frying oil with fresh oil slows down the hydrolysis of frying oil. • Large amount of water in food being fried hydrolyze the oil rapidly.1/5/2018 16Y.BAVANEETHAN
- 17. Free fatty acid value is used to monitor the quality of frying oil during a frying process. Oil and water do not mix except at high temperature under high pressure or due to surfactant during frying. Presence of surfactant is considered majorly responsible to facilitate formation of oil and water solution during frying causing hydrolysis reaction. Sources Fresh oil can have may be due to chemical refining process, poor bleaching, washing Foods – metal ions reacts with FFAs forms soap Poor rinsing of the fryer after cleaning 1/5/2018 17Y.BAVANEETHAN
- 18. Lipid oxidation during frying highly complex, => since both oxidative and thermal reaction occur simultaneously Oxidation during frying causes most significant changes in flavors of fried foods both desired and undesired Thermal oxidation mechanism similar to autoxidation, but faster. Autoxidation of unsaturated fatty acids initiated by free radicals in the presence of Oxygen – during frying, air pulled into oil Metals (iron, copper, nickel etc.) – food or oil As the temperature increases, solubility of oxygen in oil decreases, although the degradation reactions are accelerated. 1/5/2018 18Y.BAVANEETHAN