For the texture of a sauce, its actually so-called mouthfeel is largely determined by its thickness. And for the thickness, the scientists usually refer to thickness as viscosity. So you wonder what viscosity - the definition of viscosity. So the viscosity, in fact, is a kind of description or try to describe how fast a liquid will fall when there is a particular pressure. So you wonder when we try to have a liquid - when we try to apply pressure onto it so basically the liquid will start to flow. But how the liquid can flow is actually the molecule inside the liquid has to come over the other or parts one in another so that the liquid can flow. So that actually create resistance or friction and it cause the viscosity. For layman understanding, you might actually think of, for example, liquid - if it contained or inside the liquid you've got really large molecule inside the liquid, so you probably know that this - the viscosity is higher. So do you know why? I think the immediate explanation is - is because it's really difficult for a larger molecule for it to go over one another. So that means it creates resistance or friction. Not only large molecule; sometime for some molecule which has irregular shape, it also create extra resistance for one molecule to over another. Now, I'm going to have a demonstration in showing how the viscosity different between an orange juice and a syrup. Now, Sue Yu, will you please try to show the audience that this - the one on my right hand side is a syrup; the one on my left hand side is orange juice. Now, what we're going to have, we're going to have two magnet with a similar weight, so when we just drop two magnet into the two different liquids, the syrup - it actually goes slower whereas orange juice, the magnet just simply sunk. Now, the thing is the explanation of why the syrup actually has high viscosity is, as you all know, that syrup contain lots of sugar molecules, which is much larger. So it actually create a high viscosity compared to orange juice because orange juice simply composed of dilute and really small molecules. So it's really easy for orange juice to flow through. I'm going to use this little animation to show a large molecule and a small molecule. As shown in this animation, a small molecule is really easy for it to go through into the bottom. For those larger balls, which is much bigger, it takes longer time. So in - in terms of molecular, how a small molecule and large molecules behave. So what's inside the sauce? In fact, it's composed of two parts. The first one is so-called the continuous phase, whereas the second one is so-called the dispersed phase. So when we try to prepare the sauce, the main objective is how we can able to create the sauce consistency. And in fact, the sauce consistency can be tuned or achieve by using the different proportion of the continuous phase and also the dispersed phase. Like, for example, if we just tried to make the sauce become less viscous, we get more continuous phase. On the contrary, if we think that the consistency of the sauce is not enough, then we can able to add more dispersed phase - that is, the thickener - to make the sauce become more viscous. You may wonder why the dispersed phase can able to increase the viscosity of a sauce. It's the main reason is actually because the thickener, in fact, is serve as - more or less as the object to obstruct the movement of the continuous phase. And in most of the cases in the sauce, the continuous phase is water. So this is the structure of a water molecule. So if - the function of the continuous sauce is to try to hold or to bath all the component inside the sauce. In most of our recipe, I guess water is one of the major continuous phase we normally use. When we try to add different component, for example, like solid, liquid or even gas, they all can serve as a kind of thickener or dispersed phase to obstruct the movement of water. So you wonder why we have to obstruct the movement of water? It's because water, in fact, is a really simple molecule. If we don't have any of these so-called dispersed phase onto the water, the water molecule can able to move freely. So that means we cannot achieve any consistency at all. So the main objective of how we can increase the consistency of water is try to add more dispersed phase. So as I just mention, dispersed phase can be solid, liquid, or even gas. So you wonder how the dispersed phase can able to increase the consistency. In fact, it can serve three different functions. The first one, as always you can imagine, is this dispersed phase - it serve as an object more or less just obstruct the movement of the water molecule, so it make the water - it's really difficult for it to move around. Now not only this, for dispersed phase sometimes, it can divide the continuous phase into different component or different quantity so that they can still maintain a certain coherence; so that it can stop or to increase the viscosity by actually divide the - all the small mass or different area in a more coherent way. And thirdly, some of the molecule, they can able to bind with water so that - make the water availability is much less compare to the thing that is - it - what at water before so that it reduce the fluidity of the continuous phase. Now this diagram actually shows how the physical structure of a sauce looks like. As what you can see, we have continuous phase mostly - in most of recipe as we mention is water, but in some case, what we can use - also we can use fat as a continuous phase in some of our recipes. But what you can see from this diagram that dispersed phase is more or less just evenly distributed inside the continuous phase to serve as a kind of object to obstruct the movement of the - of the continuous phase. So this kind of dispersed phase can be many thing; it can be plant tissues or solid, or it can be droplets or liquid form or sometimes it can be bubble of air.
