Bsc 1st Year -Effect of Heat

Effects of Heat on Food:

 

Foods are composed of protein, fats, carbohydrates and water plus trace elements like minerals, vitamins, pigments and flavor elements. It is important to understand how these elements react when heated and when mixed with each other. You must understand why foods behave as they do and then you can get them to behave, as you want them to.

 

PROTEINS

 

1. Protein is a major component of meat, fish, poultry, egg and milk. It is present in smaller amounts in nuts, beans and grain.

2. As proteins are heated, they become firm and coagulate. As the temperature increases, they shrink, become firmer and lose more moisture. Exposure of proteins to excessive heat toughens them and makes them dry. Most proteins complete coagulation at 160-185F (71-85C).

3. Connective tissues are special proteins that are present in meats. Meats with a great deal of connective are tough, but some connective tissues dissolve when cooked slowly with moisture.

4. Acids such as lemon juice, vinegar and tomato help to speed coagulation and also help dissolve some connective tissues.

 

 

CARBOHYDRATES

 

1. Starches and sugars are both carbohydrates. Both compounds are present in foods in many different forms. They are found in fruits, vegetables and grain plus in beans and nuts. Meats and fish contain only very small amount of carbohydrates.

2. For a chef, the two most important changes in carbohydrates caused by heat are caramelization and gelatinization.

 

 

Caramelization is the browning of sugars. The browning of seared meats and the golden crusts of bread loafs are forms of caramelization.

Gelatinization occurs when starches absorb water and swell. This is a major principle in the making of sauces and the production of bread and pastries.

Acids inhibit gelatinization.

 

 

 

FRUITS & VEGETABLE FIBER

 

1. Fiber is the name of a group of complex substances that give structure and firmness to plants. This fiber cannot be digested.

2. The softening of fruit and vegetables in cooking is the part breakdown of this fiber.

3. Sugar makes fiber more firm. Fruits cooked in sugar remain more firm.

4. Baking soda and other alkalis make fiber softer. Vegetables should not be cooked with baking soda because they become mushy and also lose their color and the vitamin content.

 

 

FATS

 

1. Fats are present in meat, fish, poultry, eggs, milk products nuts and whole grain and to a lesser extent in vegetables and fruit. Fats are also important as a cooking medium and for frying.

2. Fats could either be solid or liquid at room temperature. Liquid fats are called oils. Melting points of solid fats vary.

3. When fats are heated, they begin to breakdown. When hot enough, they deteriorate rapidly and begin to smoke. The temperature at which this happens is called the smoke point and it varies for different fats and oils.

 

 

MINERALS, VITAMINS, PIGMENTS

1. Minerals and vitamins are important to the nutritional quality of the food. Pigments are important to a food’s appearance.

2. All these components may be leached out, or dissolved away from foods during cooking.

3. Vitamins and pigments may also be destroyed by heat, by long cooking and by other elements present during cooking.

4. It is important, then, to select cooking methods that preserve, as much as possible, a food’s nutrients and appearance. These will always be a consideration when cooking techniques are involved.

 

 

HEAT TRANSFER

 

In order for food to be cooked, heat must be transferred from the heat source (such as a gas flame or heating element coil) to and through the food. Understanding the way in which heat is transferred and the sped at which it is transferred helps to control the cooking process. Heat could be transferred by Conduction, Convection or Radiation.

 

Conduction – occurs in two ways:

1. When heat moves directly from one item to something touching it.

2. When heat moves from one part of something to an adjacent part of the same item.

 

Different materials conduct heat at different speeds. Heat moves rapidly through copper and aluminum, more slowly through stainless steel and slower yet in glass and porcelain. Air is a very poor conductor of heat.

 

Convection – Convection occurs when the movement of air, steam or liquid (including hot fat) spreads heats. There are two types of convection:

1. Natural. Hot liquids and gases rise, while cooler ones sink. Thus in any oven, kettle of water or deep fat fryer there is a constant natural circulation that distributes the heat.

2. Mechanical. In convection ovens and steamers, fans speed the circulation of heat. Thus the heat is circulated much faster and more evenly and thus the food cooks faster.

 

Stirring is a mechanical form of convection. Thick liquids cannot circulate as quickly as thin ones, so the rate of natural circulation is slower.

 

Radiation - Occurs when energy is transferred by waves from the source to the food. The waves themselves are not actually heat energy but are changed into heat energy when they strike the food being cooked. There are two types of radiation used in the kitchen:

1. Infrared. Broiling is the most familiar example in infrared cooking. In a broiler, an electric element or a ceramic element heated by a gas flame becomes so hot it gives off infrared radiation. which cooks the food. There are also high intensity infrared ovens, designed to heat food rapidly.

2. Microwave: In microwave cooking, the radiation generated by the oven penetrates part way into the food, where it agitates the molecules of water. The friction caused by this agitation creates intense heat, which cooks the food. Because microwave radiation affects only water molecules, a completely waterless material will not heat up in the microwave. Plates become hot only because of the conduction of heat from the food. Also, because microwaves penetrate no more than 2” into the foods, heat is transferred to the center of large pieces by conduction.

 

 

 

COOKING TIMES

 

 

It takes time to heat a food to the desires temperature, the temperature at which food is done (meaning the desired changes have taken place). This time is affected by three factors.

 

1. Cooking temperature

This means the temperature of the air in the oven, the surface of the griddle,

or the liquid in which the food is cooking.

2. The speed of heat transfer

Different cooking methods transfer heat at different rates. Frying and sautéing are faster than roasting.

3. Size, Temperature and individual characteristics of the food

For example –

A small piece of meat cooks faster than a large one.

A chilled piece of fish takes longer to broil than one at room temperature.

Seafood cooks faster than lamb and chicken.

 

Because there are so many variables, it is impossible to determine the cooking time in a recipe. The chef must use his or her judgement to make the final evaluation of the doneness of the food.