1.2: What is energy?

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From the course by The Hong Kong University of Science and Technology

The Science of Gastronomy

195 ratings

The Hong Kong University of Science and Technology

The Science of Gastronomy

195 ratings

This course introduces a number of basic scientific principles underpinning the methodology of cooking, food preparation and the enjoyment of food. All topics covered have a strong basis in biology, chemistry, and physics application. Among others, they include the consumption of cooked food, the physiological and evolutionary implication of the senses, geographic and cultural influences on food, and the rationale behind food preparation. We will also discuss issues such as coupling of senses to improve sense stimulation; altering flavor by chemical means; and modification of the coloration to improve the appearance of dishes. Following the video demonstrations of the scientific principles of cooking, you will learn to recognize the key ingredients and their combinations for preparing good healthy food. At the end of this course, you will be able to: - appreciate the scientific basis of various recipes; - develop your own recipes by integrating some of the scientific principles into new dishes; - recognize the influence of the material world on human perception from the different senses; - appreciate the art of integrating science into cooking and dining. Important Note: This course is not designed for people with special dietary needs such as vegetarian, diabetic, and gluten-free diets. If you feel uncomfortable with any part of the assignments or activities of this course, you can substitute some of the ingredients or ask friends and family members to help with the tasting of your assignments. Alternatively, you may skip that specific assignment provided that you have fulfilled all other qualifying requirement to pass the course. Course Overview video: https://youtu.be/H5vlaR0_X2I

From the lesson

Orientation, Module 1 and Module 2

This week, we will focus on “Energy Transfer” and “Hunger and Satiety”. Before you start with the content for these modules, please watch the Course Overview, review the Grading Scheme, and read the Important Note on special dietary needs.

1.0: Introduction8:33

1.1: Energy Transfer - Topic Outline0:35

1.2: What is energy?5:22

1.3: How energy can be transferred through conduction?7:19

1.4: Demonstration - Comparing heat capacity3:52

1.5: Demonstration - Comparing heat conductance4:57

1.6: How do we cook by convection?10:48

1.7: Demonstration - Increasing boiling point with salt1:26

1.8: Demonstration - Cooking medium and convection2:19

1.9: Can radiation and phase transition be used in cooking?8:15

1.10: Energy Transfer - Topic Summary1:07

Meet the Instructors

King L. Chow
Professor
Division of Life Science
Lam Lung Yeung
Associate Professor
Department of Chemistry

Welcome back.

Let's talk about Gastronomy the next section.

About cooking via the heat transfer.

Now when we talk about heat transfer in cooking, there

are few concepts that actually we are going to do,

including the mixing of food, including heating up something using

your utensils, so that we can heat up the food.

We can talk about the chilling so that the food can

be raised to a high temperature, and we cool it down

to a low temperature. Oh, we'll talk about freezing.

Basically, you want to have the food frozen.

Now all of this would involve the transfer of energy,

and we are going to talk about one by one.

Now energy, as we understand, can exist in multiple forms, such as chemical energy.

Chemical energy usually are the energy which are stored in

a substance where they keep all this molecules and atoms

bound together. That's called chemical energy.

Electromagnetic energy.

These are the energy which can be transmitted in wave form so that

it can go from one place to the other without any medium in between.

And that's referred to as electromagnetic energy.

Kinetic energy. It is very easy to understand.

When you move around, you have motion, you have vibration.

You migrate from one place to another place.

That's referred to kinetic

energy, movement is involved. Thermal energy is very easy to understand.

It's talking about the change of temperature.

So from very low temperature to high temperature.

We say that that's a increase of thermal energy.

And finally, potential energy.

When we have any kind of, such as a bottle,

when we move it from one place to the other.

Basically we would have energy stored in them in a potential form that can be used

later on. That is called the potential energy.

Now, all this energy form, they are interconvertible.

Essentially, it's following the law of thermodynamics.

Energy can be transferred from one form into another form.

Now, let's look at actually how heat energy is being transferred.

When we say that heat, when it is in atomic scale,

we are talking about how this kinetic energy of a molecule or

a substance when they, being transferred from one

place to the other place through movement of molecules.

Now, so all this would involve the change of

position, change of orientation, and change of their vibration frequency.

And all this results in increase or decrease of the heat energy.

Now in this whole process, when some substance

is changed from low kinetic energy to

high kinetic energy, we call that heat transfer.

Now, of course what we're dealing with is including chilling,

freezing, heating, and all these things essentially we use in cooking.

Now, how about temperature?

Temperature, in a way, is a very convenient way for

us to measure what that kinetic energy is really is.

We are referring to, what's the average speed

molecule or substance. They are moving.

Now, so the higher the temperature, that means

they are more active, the faster they are moving.

The lower the temperature, basically they are

more stagnant, they are not moving around.

And of course at the, a condition of

absolute zero, that is in minus 273.15 Celsius degree.

What we have is that basically, the molecules or the particles,

they stay without any motion.

And in that situation, we call it absolute zero.

When we talk about heat and temperature in actuality, we

talk about how heat flow from one place to another place.

So I want to introduce to you a very

simple equation, not that I want you to remember it,

but that highlights some of the key elements of this

so called heat and temperature, and the flow of energy.

Now, basically the flow of energy can be highlighted in this, marked by Q.

Q is amount of energy.

And t is amount of time.

So therefore, amount of energy transferred per unit time, that's

referred to the rate of the heat transfer, or heat flow.

And this is affected by a few parameter, including k,

marked here, referring to the very characteristic property of a substance.

This heat is transferring through.

A refers to the area, that means how

large area this energy is being transferred through.

Delta T refers to the temperature difference, whether it's going from a very

high temperature to a very low temperature,

or they only differ by very little.

So of course, the higher the difference between the

two temperature, the faster the flow of the energy.

Yes. And of course, finally, L.

L refers to the distance between this two source.

One is the energy source.

The other one is the sink where the energy is flowing to us.

Now,

having that, I want to highlight that when we are cooking,

we usually deal with a few ways that heat is being transferred.

Usually, they are done by

conduction, convection, radiation, vaporization, or condensation,

and sometimes we refer to that case as a phase transition.

All this would involve transfer of heat from one form to the other form.

Now, with that, let's take a break, and we'll

look at each of them and see actually, what's the principle behind them.

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