So I’ve been making yogurt at home again. I figured it’s worth it since I eat quite a bit of yogurt every week, and it isn’t exactly cheap. Target, for example, sells their cheapest yogurt for about $0.09/oz ($2.99 per 32oz container), but it also sells milk for about $0.03/oz ($4.19 a gallon). Since a gallon of milk turns into a gallon of yogurt (unless you strain the liquid out to make greek yogurt), I can have yogurt for just a third of the cost!

The first time I made yogurt was four years ago, and I’m still surprised that all you really need are two things:

• Milk
• Plain store-bought yogurt

Of course, there’s the optional fruit or honey or sugar that you can add to it depending on your preferences. The milk can be whole milk, 2% fat, or 0% fat—as long as it’s not lactose-free, you should be fine. You need the lactose because that’s what the bacteria eats. Where do you get the bacteria? You can get that from yogurt that you bought at the store. Make sure it has live and active cultures in it.

There are good resources online that teach you how to make yogurt like Bon Appétit and NYT Cooking, but the gist is:

1. Heat the milk until it starts to steam. Make sure to heat it slowly and occasionally stir so that you don’t burn the milk.
2. Let the milk cool down. For me, I just let it sit to cool for around 20 mins or until it’s just warm to the touch. (Wash your hands! I’d use a thermometer, but I unfortunately don’t have one at home.)
3. Add your store-bought yogurt. Mix thoroughly until it dissolves to distribute the bacteria evenly.
4. Put it in the oven with just the light on. This should keep it warm enough to encourage the bacteria to grow.
5. Wait for 12 to 24 hours. The longer it ferments, the thicker and more sour it gets.
6. Take it out and put it in the fridge. The yogurt will thicken even more as it cools down.

And you’re done! You can use this yogurt to make even more yogurt in the future.