9.3: Things to know when changing the viscosity of a sauce

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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

Module 8 (continued) and Module 9

This week, we will continue our focus on the preparation and cooking of meat and learn about the elements that affect the preparation of sauces.

9.0: Sauces - Topic Outline0:56

9.1: The Importance of sauce in a dish3:23

9.2: Sauce and viscosity8:37

9.3: Things to know when changing the viscosity of a sauce10:40

9.4: Changing the viscosity of a sauce I: Larger or smaller molecules?13:04

9.5: Changing the viscosity of a sauce II: Particles and bubbles16:17

9.6: What makes an ideal sauce?5:59

Meet the Instructors

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

So what are the basic principle behind the sauce making?

Now, as we all know that for sauce making,

the most important thing is how we are able to make

the consistency with the real perfect texture and with the flavor.

Now, there is some sort of general understanding about when we try to prepare our sauce.

Now, when we try to prepare a sauce,

which we need a really viscous sauce,

we either can - actually,

this is a kind of general understanding that is we try to make a source viscous,

we can add different ingredient like,

for example, sugar, starch, or even protein, right?

Now, when we try to add

these different molecules there - so have you ever think of like, for example,

some molecule, for example,

in order to make it - the sauce become really viscous,

we have to add more of these kind of molecules.

On the contrary, some molecules - only -

we add only tiny amount or really small amount of it,

we had already mixed the sauce with really viscous.

So the main difference between these two effect if, for example,

if we need to add quite a lot of - or a large amount of molecule to mix a viscous sauce

and this kind of molecule can have a huge effect in the flavor.

But on the contrary,

for some of the molecules - like, for example,

starch - since we only add small amount of this starch,

we can already make a really viscous sauce.

So for this kind of molecule,

it doesn't have too much effect in terms of the flavor.

Now, these are the four factors

in terms of the so-called physical factors which can affect the viscosity of the sauce.

They are temperature; concentration of the solute,

that is how much we dissolve into the sauce;

the third one is which type of molecule is being put in the sauce;

and finally, the substances,

or the matter - what we are going to add on the sauce.

As I just mentioned,

for this kind of matter,

suspended matter, it can be solid,

it can be liquid, or it can be gas.

The first one, when we go into the effect of the temperature in terms of viscosity;

so this actually tells you how temperature effect the viscosity.

When the temperature actually increase, what you can see,

it end up with the viscosity actually decrease.

The main reason is if we try to increase the temperature of the sauce,

the average speed of all the molecules inside the liquid or the sauce start to increase.

So that actually decrease the contact time of these these molecules.

So you end up with so-called a decrease in the viscosity.

So I'm going to do a demonstration.

Su Yi now try to - by applying this kind of principle in making a so-called white sauce.

Now firstly, what we are going to do is we add butter

to melt. So what we're going to do in the next step - okay,

we're going to add flour onto the melt butter.

So this is the flour;

we just add onto it.

So the flour actually more or less evenly distribute or disperse in those melt butter.

So you wonder what is the continuous phase.

So the continuous phase,

what we're going to use today is the milk.

So this is how we prepare our white sauce.

Okay. So once it add in.

So how I'm going to tell you the effect of temperature on the viscosities over here.

Right now I'm going to use a temperature sensor.

So the temperature reading is being showed in this iPad.

So when I try to warm it up,

you can see the temperature actually increase.

So you wonder what's the temperature of the white sauce right now?

So I put the probe in here.

You can see the temperature just go up to about 70 degree.

So for this liquid,

it doesn't show any consistency at all.

But however, when I try to lower the temperature,

cool it down, you can see the viscosity will increase a lot.

So the temperature right now is still about over 70 or close to 80, right? Okay.

So, what Su Yi going to do right now is you're going

to - is start to thicken a little bit.

So the consistency starts to generate here.

Right? And so the temperature right

now is about 80 degree.

Okay. So what we're going to do is we try to cool it down.

So we just power off.

So when the temperature actually starts to fall - so this is become more viscous, right?

All right. And the temperature right now before below 80.

So thank you, Su Yi.

So we actually demonstrate how the temperature effect on the viscosity of the sauce.

The second factor which affect the viscosity is actually the concentration of the solute.

So the meaning of solute is actually how much of the material dissolve in water.

Like, for example, we have different concentration of sugar.

Like, for example, in this case,

what I'm going to show you later is different concentration of syrup.

As all you know - or you all know that syrup actually contains sugar molecules.

So If the concentration of the sugar present in the water is increased,

the viscosity - later on you will see - will increase.

Same thing.

You may wonder why the increase of the solute will increase the viscosity.

It's because the solute more - mostly is - actually,

it's a much larger molecule.

It actually obstruct the flow of the water molecules.

I'm going to use a demonstration to show you

how different concentration of solute can affect the viscosity of some sauce. Su Yi.

So what Su Yi is going to do is actually,

we have a bottle of honey.

I guess you all know that honey contains sugar dissolved in it.

So what I'm going to show you is that I'm going to dilute the bottle

of honey with water to make a new solution.

So basically - well,

you can see the honey still can able to dissolve in water to form a new solution.

So when we tried to mix it until it become more or less homogeneous

- so what Su going to show you is

the different viscosity of these two different solutions.

Firstly, Su going to use a plate to show how

this diluted honey actually will so slide.

So you can see, it's more or less - still,

it can flow freely.

But on the contrary, for this honey - so what you can see

is still really viscous.

So it shows actually different concentration of solute.

It has different effect on the viscosity.

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