 I'm sure you know that yogurt comes from milk but did you know that bacteria are also a key ingredient? Yes, bacteria! But don't worry, these are good bacteria and are often called probiotics. Your gut has thousands of types of bacteria happily living inside whose job it is to aid digestion. Yogurt is thought to be a good vehicle to bring more of these good bacteria in. So in this video we're going to learn a bit more about how yogurt is made. First we need milk. Before we start the next steps all of our equipment needs to be sterilized to kill any unwanted bacteria and other microorganisms. Now we're ready to start. The milk is heated to somewhere between 85 and 95 degrees Celsius for between 15 and 30 minutes. This is a process called pasteurization and is also done to kill any bacteria and other microorganisms that are naturally found in the milk. The milk is then homogenized. This breaks down the fat droplets in milk to make them smaller so that they stay suspended in the yogurt, rather than sinking and making it all lumpy. So we've sterilized our equipment, then pasteurized and homogenized the milk. Now the mixture is cooled to 40 to 45 degrees Celsius and we add our special yogurt making bacteria. The mixture needs to be cooled first so that the bacteria aren't killed by the high temperature. You might be wondering why on earth are we adding bacteria when we've gone to all the effort so far of killing all the bacteria. We're adding lactic acid bacteria, which are also used in cheese manufacturing. The two species used to make yogurt are lactobacilli and streptococci. But don't worry you don't need to learn these names. Just remember that lactic acid bacteria are added. These lactic acid bacteria are known as the starter culture. The bacteria ferment the milk and change it into yogurt. Lactose is the main sugar in milk and during fermentation the bacteria turn the lactose into lactic acid. The bacteria also start to digest the milk proteins. Fermentation takes many hours and during this time the mixture skipped at the optimum temperature of 40 to 45 degrees Celsius so that the bacteria can work its fastest. As fermentation produces lactic acid type of acid the pH of the milk drops to about pH 4.4. This is why natural yogurt has a sharp tangy taste. As the pH levels drop the milk solidifies to become raw yogurt. Once the pH drops to a low the lactic acid bacteria that make the yogurt also stop working so the yogurt doesn't become too solid. The pH drop also stops any bad bacteria growing. The solidification happens because the proteins begin to coagulate. Coagulation is when something which is liquid turns into a more solid state. So we've sterilized our equipment, then pasteurized and homogenized the milk. Add lactic acid bacteria so fermentation happens and then coagulation. The mixture is now stirred and cooled to 5 degrees Celsius and we've made natural unflavored yogurt. At this stage we can add flavorings and fruit. Now it's ready to be packaged and sold delicious. Can you match the words to the definitions of the different stages of the yogurt making process? Pause the video and give it a go. Did you get them right? Now what about completing the missing words? Again pause the video and work them out. Did you get them right? So there we have the process of yogurt making, from milk to a tasty strawberry flavored yogurt. If you like the video give it a thumbs up and don't forget to subscribe, comment below if you have any questions. Why not check out our few school app as well. Until next time.