If you want to make your own yogurt, then you're going the need a starter culture. This is a collection of bacteria that, when introduced to your ingredients, will breed and multiply. Once you have a starter culture, making yogurt can be simple. However, you may have a few questions about yogurt starters at the onset. Hopefully, you'll find answers to those questions below.

What is the difference between heirloom cultures and direct-set cultures?

These are the two key types of cultures that you'll see for sale. They're quite different from one another, so it's a good idea to know what each one is. Direct-set cultures are made for one-time use. Usually, the starter will be inside a packet, and you'll empty that single packet into your yogurt recipe. An heirloom culture, on the other hand, is a culture that you will keep in your home for a long time. You'll use some of it in your yogurt recipe, and then you'll feed it again to bulk it back up. You can use it each time you make yogurt.

Should you buy an heirloom or direct-set culture?

That depends on your plans! If you only think you're going to make yogurt one time, then a direct-set culture is probably your best bet. If you think you're going to make yogurt again and again, and if you don't mind the upkeep of an heirloom culture, then the heirloom culture is the better value over time,

What are mesophilic and thermophilic cultures?

Mesophilic yogurt cultures are those that proliferate at middle temperatures. The word "meso" means "middle." They go best at room temperature—around 70 to 80 degrees, roughly. Thermophilic yogurt cultures love the heat. They do best at around 100 F. 

Which one you need depends on how you intend to make your yogurt. Will you be letting it rest at room temperature? Then you need a mesophilic culture. Does your recipe call for it to rest in a hot water bath? Then you need a thermophilic culture. Usually, using a mesophilic culture is easier your first time around, but it comes down to your preference and plans.

Hopefully, you now have a bit of a better understanding of yogurt cultures. Since cultures tend to be pretty affordable, you can usually buy a few different types and experiment a little if that's what appeals to you. Contact companies that supply greek yogurt starter cultures to learn more.