So, cooking involve heating. So you wonder how heating effect the meat's textures. So, here are the three major changes when we try to heat up our steak. The first one is concerning about the water-holding capacity. The second one is about there's a change in the muscle fibre. The third one is about change in the connective tissues. Now, let's look at the first one. What happened when we tried to heat our meat, the change in terms of this water-holding capacity. Initially, when we try to cook the meat, what you experience is the meat won't get fried. Because although the meat, when we try to cook it, water continues to evaporate. But however, if we try to cook it in the very initial time, there's hot inner change in terms of the water-holding content. The reason is because there's always a continual supply of the water, so-called the bound water inside the meat. As long as the bound water continues to supply the so-called water lost, what we will experience about the meat structure, we experience it won't dry at all. So, here comes the equation. So if the free water lost during heating is equals to the weight of converting those water hold in the muscle fibre, what we will experience is the meat still retains its juiciness. However, at a much higher temperature, changes will stop to take place. Like for example, if we heat it at about over 70-degree for long period of time when the conversion of bound water is not sufficient to replace the lost of free water, then what we would experience is our meat will start to get dry. Apart from the water content, change inside our meat fibre. Also, what we will experience is turn of the meat textures inside the meat muscle fibre. Since the muscle protein, what we will experience is when we heat for a long period of time, what we know is the meat will get tough and become less tender. One of the reasons is because the muscle fibres contain myosin. This myosin, when we try to heat it up at high temperature, it becomes less soluble and the protein will start to shrink. Here, I like to show you a animation about the change of muscle when we try to heat it up at elevated temperature. As temperature start to go up to about 50 degrees, what you can see the muscle fibre start to shrink and not only for the muscle fibre start to shrink, the color also start to change. And eventually, this shrink of the muscle fibre, it will move the loss of the water molecule. Then what we are experience is the leech become really tough and dry. How about the change in the connective tissues? As you all know, the connective tissue, the main function is try to hold all the muscle fibre together and is actually lined between all the muscle bundle. However, when we try to heat the so-called the connective tissue is the connective contain lots of collagen and it will slowly convert it to gelatin. And basically, if we try to heat it for a long period of time, this collagen will slowly convert to gelatin. So you wonder, what's the structural difference between collagen and also gelatin? One of the major different is actually for the collagen itself is actually open. But however, for the collagen itself is actually translucent in color. The main reason is why there is a color change transform the opaque to become a translucent is because of the structural change. These two diagrams indicate the main structure about the collagen and also the gelatin. In the collagen, it contains three strips of protein. It actually coil with each other. And when a point, high temperature. If we try to heat it for long period of time, these three strip of protein become unwind, become the gelatin. So since the structure, it's much more simpler compared to the collagen itself. That's why the color changed from opaque to become translucent. Now I show you, here is the bit come from a cow tail. What we can see, we can see lot's of white tissues just in between the muscle fibre and what you can see is opaque in color. But however, when we cooked it for long periods of time, this connective tissues start to change to become opaque in color, become translucent in color and not only it changed to translucent. That means it changed to a gelatin. But also when we look at the muscle fibre, it just shrunk to let more bones to appear in the photos. Now after knowing, that is the changes. Now, I want to actually tell you how we can able to check whether the meat has been finished cooking or not. So especially for steak, there's three categories. One is rare, medium and well done. So you wonder how we can able to check whether our steak is in rare state, medium or well done. One of the most simplest way is by using our finger. So here, it shows when we try to touch our index finger with a thumb. So when we try to sense it, feel it. It's actually soft, what we call is rare. However, for the middle finger. So this is the medium whereas the last finger, this is well done. So you experience your muscle, your really tough in this stage. So instead of simply using this finger test, the other thing, what we can able to check for the meat's doneness is by looking the appearance. So in looking the meats color, we can know whether our meat has been finished cooking or not. Basically, we can able to determine whether it is rare, medium or well done. The main reason is if you still remember, that is the meat fibre contains myoglobin. So when we try to heat it, it stop to oxidize. As the myoglobin contain the iron molecule in the molecule center. So when it oxidized from iron II to iron III, when oxidized, it actually changes, the color changes from red to become brown. So the longer period of time you heat it up, the more the iron will oxidize from iron II to iron III. That means if it will stop to change to brown in color. So, we can use the color in judging the doneness of the meat. This is a good picture in showing the steps of the doneness of the meat, this bacon. So in this part, what you can see, the appearance of the meat appears to be red in color. So, you can see that it is rarely being done. But however, as you go along the meat, you can see a completely well done part in the inner part of the photo. That means it is brown in color. So simply by looking at the meat appearance, we know whether our meat has been go to our state that we want whether you like to have a rare, medium or well done.
