One would assume this is a simple question, because we are all familiar with yogurt. It turns out there are more forms of it and methods of creating it than most folks realize.
In the USA, yogurt by regulation is a coagulated milk product that at a minimum was coagulated using the culture Lactobacillus delbrueckii ssp. bulgaricus. Usually yogurt is cultured using a mix of cultures, but it should at least have that culture included. But there's much more to the story: any milk, coagulated to at least a loose consistency using LAB bacteria, usually thermophilic, and then eaten fresh could be termed a yogurt. When making mother cultures milk is coagulated by the desired cultures to that consistency, and so many mother cultures even lacking bulgaricus bacteria are rightly called yogurt. Clabber, especially the thermophilic version, is most likely a form of yogurt.
While mesophilic cultures can be used to make a yogurt or at least a yogurt-like dairy product, most people don't think of this as yogurt, but it is an extremely related product. Generally, yogurt is made with thermophilic cultures such as S. thermophilis (ST), bulgaricus as mentioned above (LDB), Bifidobacterium lactis (BL), L. Acidophilus (LBA) and more, and it is fermented and coagulated at a temperature of 110 F. In North America, thicker yogurts are more popular, so the milk is often heated to about 185 F and held for 15 minutes to denature many of the proteins in the milk, and then cooled to 110 F for culturing and held for 4-12 hours (usually 6 is sufficient), which produces a thicker-set yogurt. In Europe, yogurts with a looser consistency are also common, where the milk is not heated, it is simply warmed to 110 and cultured and held until coagulation, which takes longer than the cooked version does.
Yogurts are often highly probiotic because many or even most of the strains of LAB used to culture the yogurt can survive in the digestive tract and contribute positively to gut health. Many are sold touting this feature prominently. Be aware that not all cultures listed as active in a yogurt are truly probiotic, but usually at least some are.
Greek yogurt is essentially a yogurt that's allowed to acidify completely and then drained of any separated whey. It makes for a more dense yogurt, and is moving along the spectrum toward a yogurt cheese.
Greek style yogurts are often made with skim or low-fat milk so the relative percentage of the yogurt that is protein is increased, but this is not necessary. It just needs to be a drained yogurt. Greek yogurt is also often made with cultures very similar to Bulgarian yogurt, which has a more tangy taste than some sweeter yogurts typically made in North America.
For this recipe, you will need a way to incubate the yogurt at 110 F. You can use an oven set on proof mode at 110 F, or use a jar set into a pot of water being managed by a sous-vide to keep the temperature stable, or a cooler with some jugs of warm water set inside, or a dedicated yogurt incubator of which there are several online that work very well. You will also need a freeze-dried yogurt culture of your choice.
Ingredients:
Steps: