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The Science of Yogurt

The Science of Yogurt

While the end product is nothing short of a magic potion, making your own yogurt doesn’t require any particular wizardry—just a firm grasp on what it is

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Yogurt has been feeding and curing humans for more than 4,000 years and by many accounts, it was first made in Turkey—by accident—when leftover milk was stored in not-perfectly-clean containers. When the milk came into contact with bacteria, it solidified into a more creamy substance.

From that moment on, not much has changed in how yogurt is made: one has to merely “contaminate” milk with the right kind of bacteria. But have no fear—the bacteria is the “good kind”, or rather two kinds: Lactobacillus thermophilus and Streptococcus bulgaricus, which have proven to have all kinds of benefits to the human body.

The only real secret to learning how to make a delicious yogurt at home, without any kind of special tools, is understanding how these two kinds of healthy bacteria act when they come into contact with milk. As the basic ingredient of yogurt, milk is a suspension, made up of water and then two elements—lactose, a sugar, and casein, a protein—whose tiny molecules allow them to meld together and form a homogenous liquid. This mixture is ideal terrain for the cultivation of these two forms of bacteria. In fact, even the smallest amount sets forth a chemical reaction, called “lactic fermentation”, when lactose transforms into lactic acid.

The acidity of the substance increases and the casein molecules form a kind of web, absorbing the milk’s water and milk. And voilà: yogurt has been made! Of course, this is just a basic yogurt, which then must be elaborated upon, but it’s enough to understand the process behind making homemade yogurt. In short, the web of protein should absorb as much of the fat molecules as possible, arranging them close to one another.

And now, let’s talk practical matters. To make yogurt, you’ll need a pot, a large bowl, a ladle and a small woolen or fleece cover. Everything needs to be as clean and sterilized as possible. As for ingredients, you’ll need a liter of fresh, whole milk (if you can find raw milk, even better), and a container of white yogurt that contains the right bacteria to create an effect on your homemade yogurt. The milk should be full of fat because of the abundance of fat molecules; the yogurt should be as fresh as possible because of the abundance of the “good” bacteria.

Bring the milk to a slow boil in the pot. After it’s been boiling for a few minutes, turn off the heat and scrape the cream off the top. Cover the pot with a lid or plate. Use a thermometer and when the milk reaches the 38°C, pour about ten teaspoons of it into a bowl with 3 or 4 spoonfuls of yogurt and mix them together carefully. Turn on the oven and heat the milk and yogurt mixture to 35°-40°C, then turn it off right away (usually a couple of minutes are enough). At this point, pour the remaining milk into the bowl, mix it all, and then cover with the cloth. Place the bowl in the oven for 7-8 hours—or even 10 hours, for a better result. Remove the bowl from the oven and place immediately in the refrigerator for a couple of hours.

Now, you can add whichever flavoring you’d like: sugar, fruit, even pieces of chocolate. What’s important is that you’ve now made your own, homemade yogurt!

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