Food science CH 5

conduction:Materials used in cookware vary in their ability to conduct heat efficiently.

*Metals that are good conductors are copper, aluminum, and iron. *Cast-iron skillets hold heat well. *Stainless steel does not conduct heat as well as other metals. Since stainless steel is durable, a stainless steel pan may have a base comprised of copper or aluminum to improve conductivity. *Glass and ceramic, such as Pyrex or CorningWare, are not as effective as metals in conducting heat. However, heat can penetrate through the glass quite well. Also, these materials can be used in the microwave, which is an advantage of using them.

Convection Illustrations

*On the left, you can see convection currents moving around heated air to bake cakes. *On the right, you can see the saucepan being heated by a heat source, then the liquid being heated. Heated liquid molecules rise, while colder liquid molecules move to the bottom of the pan to be heated. These movements create convection currents to aid in distributing heat throughout the liquid.

microwaves generally penetrate about

1 to 2 inches into the food. The depth of penetration varies with the composition of the food product. *Further distribution of the heat toward the center of the food occurs by conduction.

What are three limitations to cooking food in the microwave?

1.) Surface browning: When utilizing a microwave, there tends to be a lack of browning on the surface for some foods. When baking bread, we like to see browning of the bread surface. It's challenging to get a browned surface with a microwave due to the cool air temperature inside the microwave. The temperature inside a microwaved food item is hotter compared to its surface. *Tips suggested in the book: use a browning dish 2.) Quality: The quality of food can be impaired when cooking with a microwave. Some foods need lengthier cooking times at simmering temperatures to tenderize or rehydrate. 3.) Overcooking and erupted hot water phenomena: Due to microwaves heating food quickly, overcooking can happen. If you let food cook a few seconds longer than required, the food may come out dehydrated/overcooked.

1. What is the Maillard reaction? Why exactly is the Maillard reaction desired by consumers? (1)

A Maillard reaction (nonenzymic browning) occurs when a carbonyl group of a reducing sugar reacts with an amino group of a protein. The removal of an H2O molecule occurs during this reaction. Reducing sugars include Glucose, Fructose, Galactose, Lactose, and Maltose. Sucrose is broken down into Glucose and Fructose before it can participate in this reaction. Typically, we see this browning reaction at higher temperatures but can happen at room temperature. Consumers look for this reaction with the browning of bread. This reaction contributes to the wonderful flavor of meats.

Radiation

Energy transferred as waves or rays vibrating at a high frequency

Vegetable Baked Ziti 1 T. olive oil ½ medium onion, sliced thin ½ zucchini, sliced thin, cut each slice in half 4 oz. button mushrooms, sliced 6 oz. pasta, cooked according to package directions 12 oz. marinara sauce 7 oz. ricotta cheese Dash salt Dash pepper ½ cup mozzarella cheese 1. Preheat oven to 350F. 2. Spray a 9X9 square baking dish with cooking spray. 3. In a large skillet, heat olive oil over medium heat (5-6 on burner). 4. Add onion slices to oil and cook until softened, about 3-4 minutes. 5. Add zucchini and mushroom slices and cook until softened and liquid has reduced, about 5-7 additional minutes. 6. Remove pan from heat and add pasta, marinara sauce, ricotta, salt, and pepper. Stir until well combined. 7. Pour mixture into baking dish and top with mozzarella cheese. Bake 30 minutes. 8. Allow to cool 10 minutes in pan. 1. Name the cooking method and each associated method of heat transfer used in steps 4 and 5 of the recipe. (1)

In steps 4 and 5, the cooking method used is sautéing ( dry heat cooking). In sautéing, a skillet is heated with a small amount of oil to cook the food. The media for heat transfer is fat (oil). Typically, we see high heat used for sautéing. The recipe asked for medium heat. I imagine this will help in not overcooking the vegetables. We then let the liquid reduce, which is accomplished by simmering or boiling a liquid. We reduce until we achieve the desired concentration. The associated method of heat and transfer is conduction. This method is the transmission of heat through direct contact. Skillets can be made of metal(great conductors), such as aluminum.

microwave safe Metal fork 6X6 inch square of aluminum foil Glass bowl Plastic covering on frozen entrée Paper plate White paper towel

NO NO YES(Only recommended if heat resistant and without metal) YES (Typically, will have to poke holes in order to vent) YES (Microwave safe labeled plates) YES

Vegetable Baked Ziti 1 T. olive oil ½ medium onion, sliced thin ½ zucchini, sliced thin, cut each slice in half 4 oz. button mushrooms, sliced 6 oz. pasta, cooked according to package directions 12 oz. marinara sauce 7 oz. ricotta cheese Dash salt Dash pepper ½ cup mozzarella cheese 1. Preheat oven to 350F. 2. Spray a 9X9 square baking dish with cooking spray. 3. In a large skillet, heat olive oil over medium heat (5-6 on burner). 4. Add onion slices to oil and cook until softened, about 3-4 minutes. 5. Add zucchini and mushroom slices and cook until softened and liquid has reduced, about 5-7 additional minutes. 6. Remove pan from heat and add pasta, marinara sauce, ricotta, salt, and pepper. Stir until well combined. 7. Pour mixture into baking dish and top with mozzarella cheese. Bake 30 minutes. 8. Allow to cool 10 minutes in pan. 1. Name the cooking method and each associated method of heat transfer used in step 7 of the recipe. (1)

The cooking method used in step 7 is baking. The media for heat transfer is air. Radiation, convection, and conduction are all methods used to transfer heat in baking. If I were to bake this at my house, I would use my conventional electric oven. In conventional ovens, radiation heats the food. Convection ovens are great at generating consistent heat with the mechanical fan.

Vegetable Baked Ziti 1 T. olive oil ½ medium onion, sliced thin ½ zucchini, sliced thin, cut each slice in half 4 oz. button mushrooms, sliced 6 oz. pasta, cooked according to package directions 12 oz. marinara sauce 7 oz. ricotta cheese Dash salt Dash pepper ½ cup mozzarella cheese 1. Preheat oven to 350F. 2. Spray a 9X9 square baking dish with cooking spray. 3. In a large skillet, heat olive oil over medium heat (5-6 on burner). 4. Add onion slices to oil and cook until softened, about 3-4 minutes. 5. Add zucchini and mushroom slices and cook until softened and liquid has reduced, about 5-7 additional minutes. 6. Remove pan from heat and add pasta, marinara sauce, ricotta, salt, and pepper. Stir until well combined. 7. Pour mixture into baking dish and top with mozzarella cheese. Bake 30 minutes. 8. Allow to cool 10 minutes in pan. 1. Name the cooking method and each associated method of heat transfer used to cook the pasta. (1)

The cooking method used to cook the pasta is boiling (moisture cooking). This method of heat transfer is convection. Convection in this step is the transfer of heat through the liquid currents produced by the movement of different temperature areas of a gas or liquid. We heat the water to a boil and then add the pasta. The heat is transferred from the water directly to the food. The media for heat transfer in this step is water.

1. What three components are needed for the Maillard reaction to occur?

The three components needed for a Maillard reaction consist of a reducing sugar, amino acid, and the removal of H2O. The chemical reactions that follow are fragmentation and polymerization. These chemical reactions will lead to the browning of the food. This reaction typically requires the addition of heat. Factors that affect this reaction include moisture, acidity(pH), and the temperature you cook the food.

Conduction

Transmission of heat through direct contact

Many foods can be prepared most efficiently if they are cooked partly by microwaves and partly by conventional methods. For example,

a casserole could be cooked in a microwave oven, then a crumb topping placed on it, and the topping finished by broiling in a conventional oven.

Microwaves radiate outward from their original source and can be.

absorbed, transmitted, or reflected.

Media for Heat Transfer

air, water, steam, fat

cooking can positively influence the

appearance, texture, and flavor of foods.

Plastic, glass, and ceramic containers marked as microwave safe must

be used when heating foods.

Examples of radiation are

broiling, barbequing and toasting. Dull, dark, and rough surfaces absorb radiant heat readily, while bright, shiny, and smooth surfaces reflect heat.

Most ovens have a defrost setting with a low to medium power input. The oven cycles on and off. During the off periods, the heat produced is distributed throughout the food mass. Meat should be

broken up and separated to allow even defrosting. Meat should be cooked immediately after defrosting.

Ensuring that foods are edible and safe are essential outcomes of cooking. Proper cooking destroys most pathogenic microorganisms. Some foods have an extended shelf life after cooking. For example,

canned foods keep considerably longer than fresh foods because of the high heat processing and protection from contamination once sealed in the can.

Stale bread can be freshened with heating by

conventional methods, but bread reheated in the microwave may become tough.

Convection

currents in the air or liquid distribute the heat

In most microwave ovens, a stirrer blade in the top of the oven helps to

distribute the waves; built-in turntables also provide another means of uniformly distributing energy.

Cooking also improves the digestibility and nutritive value of some foods. For example

dry legumes are not edible and must be rehydrated and softened so that they are more palatable and digestible.

Heated air as the cooking medium is considered

dry-heat cooking because the surface of the food comes into contact with dry air.

Cooking in oils and fats does not involve water and is therefore considered

dry-heat cooking. *Fat can be heated to a much higher temperature than the boiling point of water.

Sautéing, panfrying, stir-frying, and deep-fat frying are examples of cooking methods that use

fat as the cooking medium.

Microwave ovens save energy and do not

generate large amounts of heat in the home compared to when we use ovens.

Cooking and heating of foods cause changes that impact sensory qualities as well as other characteristics. Cooking results when

heat is transferred to or produced in a food then distributed throughout.

Broiling, roasting, baking, and grilling are examples of cooking methods that use

heated air as the cooking medium.

Conduction is the transmission of heat through direct contact from one molecule to the next. Heat moves from the

heated coil of an electric unit or the flame of a gas unit to the pan placed on it. *Heat is then conducted throughout the mass of the food in the pan.

Simmering, boiling, stewing, poaching, and steaming are examples of cooking methods that use

heated water as the cooking medium.

Energy can be transmitted as waves or rays that vibrate at

high frequency and travel very rapidly through space. *Waves of radiant energy travel from their heat source in a straight line to the surface of food that is placed in close proximity. *When radiant waves reach the exterior parts of a food mass, energy is absorbed on the surface of the food and produces heat by increasing the vibration of the molecules in the food.

Induction cooking utilizes a

high-frequency induction coil that is placed beneath a cooktop to produce friction to generate heat. *The induction coil will heat metal cookware containing iron, but remains cool when cooktop is not in contact with iron. *Once heated, the iron pan rapidly transmits heat to the food via conduction.

convection fans employ a mechanical fan to

increase air movement *increases effciency

In convection ovens, a mechanical fan is used to

increase convection currents and air movement, which increases efficiency and decreases baking time. Baking time and temperature should be reduced to avoid overcooking.

Microwaves do not cook from the

inside out

One of the great advantages of using a microwave oven is the speed with which cooking can be accomplished, 2 to 10 times faster than conventional methods. However, time must be

lengthened if a larger quantity of food is cooked in the microwave. *For example, one potato cooks in 4 minutes while 4 potatoes may take 16 to 19 minutes to cook.

The Food and Drug Administration regulates the manufacturing of microwave ovens in terms of performance standards and design safety. A radiation safety standard enforced by the FDA

limits the amount of microwaves that may leak from an oven. *These standards are believed to protect the public from radiation hazards.

It is easy to overcook foods in the microwave since heating is so rapid. Unevenness of heating is also a major disadvantage in the use of microwave ovens. This lack of uniformity may raise some questions about the

microbiological safety of foods heated with microwaves. *Some pathogenic microorganisms, such as Salmonella, may still be present in foods. *The internal temperature of foods must be checked to ensure food safety.

Lack of surface browning is a real disadvantage of

microwave cooking for some foods. When breads, cakes, and meats do not brown, the flavor, appearance, and texture can be negatively affected.

Metals in the walls of the oven reflect

microwaves in the oven.

Heated water as the cooking medium is considered

moist-heat cooking. *Heat is transferred or conducted directly from the hot water to the food. *Water is a better conductor of heat than air and foods cooked in water cook faster.

Steaming is also a

moist-heat method of cooking. *When cooking with steam, heat is transferred from the steam to the surface of the food. *Foods are steamed when they are placed on a rack above boiling water in a covered container or when foods that contain water are wrapped in foil or placed in a cooking bag or covered dish.

Metal containers, metal utensils, or glass containers with a metal glaze, rim, or trim should

not be used.

consumers have reported superheated water to the FDA. Superheated water has been heated

past its boiling point without appearing to boil. *When superheating has occurred, a slight movement, such as picking up the cup of liquid, may result in sudden violent eruption of boiling water and severe burns.

Limitations of Microwaves: erupted hot water phenomena

potentially very dangerous

Microwave ovens can heat pre-cooked foods and thaw frozen foods

quickly.

In radiation, Dull, dark, rough surfaces absorb

radiant heat

in radiation bright, smooth surfaces reflect

radiant heat

Heating by induction is

rapid and numerous power settings are available. Cleanup is also easy since there is no exposed heating unit and spills do not burn onto the unit. On this slide, you can see an image of an induction cooktop.

Heat is a form of energy that results from the

rapid movement of molecules within a substance. This movement of molecules is called kinetic energy.

Cookware made of cast iron, magnetic stainless steel, or enamel over steel is ____ for use on induction cooktops.

required

Foods that need long cooking times to tenderize or rehydrate are not

satisfactorily prepared in the microwave.

Microwave: Flavors may not have an opportunity to develop in

short cooking times.

reheating meals in a microwave is a great advantage of microwave cooking. Foods should be arranged for optimal cooking efficiency and evenness. For example,

the center in a mound of mashed potatoes should be pressed down and meat should be sliced thin. Denser items should be placed toward the outside of the plate for optimal reheating.

Convection is the transfer of heat through air or liquid currents caused by

the movement of different temperature areas of the gas or liquid. When gases and liquids are heated, they become lighter or less dense and tend to rise. The colder gas and liquid moves to the bottom, thus setting up circular convection currents.

In radiation radiant energy travels from

the source directly to the food placed near it •Ex: broiling, barbequing, toasting

We can measure the average intensity of heat using a

thermometer. *We record heat as temperature.

Convection currents tend to distribute the heat

uniformly. The preparation of food in water, fat, or hot air are examples of cooking using convection currents.

Microwaves are high-frequency electromagnetic waves of radiant energy. They can be described as radio waves of

very short wavelength.

Microwave ovens are great for cooking vegetables to conserve

water soluble nutrients.

convection includes

water, hot aur

Cooking Suggestions:heating meals

§Arrange foods to cook evenly

Cooking Suggestions: combined microwave and conventional cooking

§Foods cooked efficiently with desirable flavor, texture, and appearance

Microwave Safe Materials

§Glass, plastic, ceramic §White paper towels §Paper plates §Parchment paper §Wax paper §Microwave approved plastic wrap (ex: plastic on a frozen entrée)

do not use in microwave

§Metal containers/utensils §Glazed ceramic (glazing may be metal) §Items with metal trim, screws on handles/lids §Aluminum foil

Cooking Suggestions:Defrosting

§Microwave oven cycles on and off §Meat should be broken up/separated

Types of Heat Transfer

•Conduction •Convection •Radiation •Induction

Heat

•Cooking foods causes sensory quality changes •Kinetic energy *Movement of molecules •Temperature *Measurement of heat *Thermometer

Conduction: Quality of materials

•Copper, aluminum, and iron are good conductors •Cast-iron holds heat well •Stainless steel does not conduct heat as well as other metals •Glass and ceramic not conduct heat as well as metals •Allows heat to travel through glass and can be used in the microwave

Air

•Dry-heat cooking •Broiling •Roasting •Baking •Grilling

fat

•Dry-heat cooking •Sautéing •Panfrying •Stir-frying •Deep-fat frying

Why Cook Food?

•Food safety and shelf life •Ex: kill pathogenic bacteria •Digestibility and nutritive value •Making foods edible •Ex: dried Legumes •Aesthetic Appeal •Ex: golden brown crust on bread

microwave cooking suggestions: standing time

•Foods continue to cook after heating, allow several minutes of standing time

Convection currents

•Heated gas or liquid is lighter/less dense and rises •Colder gas or liquid moves to the bottom

What are Microwaves?

•High-frequency electromagnetic waves of radiant energy •Radio waves of very short wavelength •Stirrer blade in oven helps to distribute waves evenly •Turntables uniformly distribute energy to food mass •Short microwaves are reflected by metals •Microwaves penetrate 1-2 inches •Further distribution of heat occurs by conduction •Does not cook from "inside out"

Limitations of Microwaves

•Lack of surface browning •Breads, cakes, meat •Cooking periods not long enough to -Tenderize -Rehydrate -Develop flavors •Some foods (such as bread) can become tough when reheated in microwave oven

Induction

•Magnetic current generated by a high-frequency induction coil *Requires iron content *Cast Iron, magnetic stainless steel, enamel over steel

steam

•Moist-heat cooking •Heat transferred from the steam to the surface of the food •Foods placed on rack above boiling water •Foods that contain water heated in foil, cooking bag, or covered dish

water

•Moist-heat cooking •Simmering •Boiling •Stewing •Poaching •Steaming

microwave suggestions: stirring and turning

•Most microwaves have turntable

Limitations of Microwaves: unevenness of cooking

•Overcook foods •Hot and cold spots •Food safety and quality •Check internal temperatures of foods for safety

induction is advantageous

•Rapid heating •Numerous power settings •Cleanup is easy

microwave Cooking Suggestions: browning

•Some foods brown in the microwave, while others may require additional cooking methods

Advantages of Microwaves

•Speed of cooking *2-10× faster than conventional methods •Reheating precooked foods and defrosting •Less nutrient loss when cooking vegetables •Energy conservation *Less heat generated in home

Safety and Regulation

•The Food and Drug Administration regulates manufacturing of microwave ovens •Radiation standard for maximum amount of microwave leakage •Standards are to protect public •FDA checks ovens for compliance