One of the first experiments they teach kids is to add rennet to milk. A simple gesture makes for one of the most fascinating and mysterious things in the kitchen: dairy. Mostly we think that making home-cheese is a difficult task, and it's better to just buy it: which is true for certain types of cheese, yet if you master a few scientific facts you can certainly make your own.
Starting with the main ingredient: milk. Its composition varies according to the type, but, generally it's made mostly of water and a high percentage of saturated fat. To that you add sugar, lactose, casein proteins. In order to make cheese, you begin with the curdling. Practically it means you need to separate the casein from the rest and make the curd. This process is at the basis of any cheese. Lets look at what we need: a few pots for 5 liters, a foraged plastic or straw container, a food thermometer, a wooden spoon, a cotton dishcloth, a large cloth and a large strainer. The following are the ingredients: 5 liters of fresh milk, a bottle of liquid curd (you can find it at a pharmacy), sea salt, a plain yogurt.
Pour the milk in a pot: if you just took it out of the fridge wait for it to cool down (a few hours will do), if you just bought it you need to "activate" it by adding half a cup of yogurt and let it sit for a few hours. Now grab the pot with the milk in it and start heating it slowly, stirring it with a wooden spoon. The point is to heat the entire pot of milk equally. When it reaches 36 °C, turn off the heat and add the curd. The amount you should add depends on how consistent the curd is, just check the box for the ingredients. Mix well, cover the pot, wrap it up with the cloth, let it sit for an hour and a half. At this point, the curd should be done: the rennet managed to separate the casein.
Finished this step, open the lid and with a knife cut through the curd from top to bottom. Better if you make many small incisions. Wait half an hour, whisk the curd: they should look like small grains. Wait another ten minutes and heat it again slowly until you get to 50 °C. At this point, the curd should be completely separate from everything else, or the whey. Strain the liquid, save the whey, you can make ricotta with it another time. Try to filter the curd properly by adding some pressure.
Now, you can put the curd in a straw or plastic container, same ones they use to preserve ricotta. If you can't find it use a colander, remember you are actually now shaping your cheese. You must keep the curd at a temperature of 25-28 °C, at a humidity of 90%, for a whole day. There are some machines that help you through this process, but, you can also use a pot in which you need to add a little water at 40 °C, insert it in another pot, place the curd container on top. Cover the pot with the kitchen cloth and then put the lid on. You must change the water every 3-4 hours. When it's done, add salt. You need a liter of water with low chlorine, pour the water in a clean pot, add 200 grams of salt, let it melt carefully. Tear the curd out and drop it in. Wait for a few hours. Turn sides and wait another hour. You have just made your first home-cheese.