Pink slides are by authors above, and are available online at:http://www.slideshare.net/celinebruce/methods-of-heat-transfer-and-cooking-methods#

Learning Targets:CO--Understand convection, conduction and radiationLO--Tell reasons why we cook, and 3 ways heat is transferred during cooking.

With your partner, name at least 4 reasons why we cook food.

Co/con = with, togetherduc/duct=lead

A train conductor leads you to your seat

A conductive material leads heat, electricity, etc.

On the stovetop, the PAN gets hot, and heats the food. We often need to flip,

stir, or toss the food to cook it properly.

Food closest to the heat may burn if it isn’t moved and

rearranged.

For good conduction you need a pan that conducts well, and won’t be damaged by high heat.Copper and aluminum are good conductors.

Heat Conductivity (ranked from most

conductive to least)*

Material ConductivityCopper 1.0Aluminum 0.5

Steels coupled conductive bases/sides

~.25

Iron and steel .16Porcelained steels ~.10Porcelained irons ~.10Glass ceramics .0025

• Porcelain and glass are not.

Sometimes a pan made of a material that isn’t a great conductor has the bottom of the pan designed to improve

conduction.

A handle that is NOT a good conductor can help prevent burns.

THIS THIShandle one.

will stay coolerthan

Good contact helps good conduction

A warped or unbalanced pan won’t have good contact with your heating element.

Woks help food fall back to the bottom of the pan,

but a frying pan has better contact on an electric burner.

Thicker pans have more even

conduction than thin pans of the same material.

(Cast iron is a poor conductor, so cast iron pans are made to

be thick and heavy.)

Once a food begins to heat, conduction moves the heat from one molecule of food to the next,

even if the original heat came from convection or radiation.

PARTNER A: What is conduction?

PARTNER B: How can you get good conduction in cooking?

Co/con=with, togetherveh/vey/vect=carry (vehicle, convey)

In convection, currents carry the heat.

Convection heats with currents in air or liquid. Heat rises; as it cools it begins to fall.

ALL ovens use convection!• In

conventional ovens the heat

creates its own currents.

• In special convection ovens fans increase the convection currents.

• The fans move the heated air around in the oven, distributing it more evenly than a regular oven. Food is heated faster & more evenly with less burning.

• You can also put a lot more in the oven.

To help conventional oven currents work well:

Cook in the middle of the oven where

temperatures are most correct.

If you cook at the bottom of the oven, the air under your food is very hot, and the air on top is

cool. You are likely to burn the bottom of your food.

Don’t expect to get good convection currents if you block them, or try to cook 2 big pans at once.

This would work in a convection oven, but not in a conventional oven.

Two small pans should be offset to balance

circulation.

Leave at least 2” airspace all around pans in a conventional oven.

In an oven, the heat comes from all around your food, so the conductivity of

the pan is less important.• But as you can see in the

picture, the pan does affect the temperature of cooking.

• Light pans reflect heat.• Dark pans absorb more

heat.• Pans with sides make it

harder for heat to surround individual items.

On top of the stove, stirring a liquid helps it cook evenly, since it creates new currents, and moves the food closest to the burner.

PARTNER A: What is convection?

PARTNER B: How can you get good convection when cooking?

PARTNER A: What is a “convection oven”?

Radi=beam, spokeAs in:

Radiation can bring heat, light, or sound

in waves or rays.

Radiator

Radiant

Broiling is an example of cooking with radiation.

• When you broil in the oven, leave the oven door open. You do not want food to bake from the heat building up in the oven, you want it to cook from the heat radiating from the unit. (Leaving the door closed could also cause the oven to get way too hot.)

Microwaves cook with radiation.

Microwave rays are not hot themselves. Microwave ovens work by making the molecules in the food vibrate. This vibration is what causes the heat.

Microwaves penetrate about an inch into foods, then conduction carries the heat the rest of the way into the food. Conduction from the food to the dish can also make your dish get hot.

PARTNER B: What is radiation?

PARTNER A: Give 2 examples of cooking with radiation.

Note from Mrs. Bryant: Although frying is done in liquid, it is still considered “dry” cooking because it does not use water.

Several types of heating can take place at the same time.

Review: Label each type of heat transfer.

B. Heat touching poker travels up the length of it.

A. Currents of warm air drift up.

c. Waves of heat come out in a straight line to hit a surface.

Which heat transfer method is shown?

Which heat transfer method is shown?

Which heat transfer method is shown?

You are making a pot roast. Which 2 heat transfer methods are shown here?

Did you reach our learning targets:

Partner B: Tell 3+ reasons why we cook food.

Partner A: Name and describe 3 ways heat is transferred: C - - - - - - - - - C - - - - - - - - - R - - - - - - - -