Yogurt is a made by fermenting milk products. This fermentation is caused by bacteria that metabolize lactose for energy and produce lactic acid. This is a process similar to the natural spoiling of milk, but the difference is that yogurt creation is controlled. In Western countries, the milk is heated to about 176°F to kill any undesirable bacteria and to allow the milk to set rather than curdle. The desired bacteria create the characteristic texture and taste of yogurt by producing lactic acid.
I often use Greek yogurt in baked recipes rather than buttermilk because it contributes the acidity of buttermilk, but elements of recipe control that buttermilk doesn’t offer. Greek yogurt has been filtered to remove much of its liquid, so using Greek yogurt allows for more water control. In addition, it comes in 0% and 2% fat which means that it is also possible to control the amount of fat in batters and doughs. The large amount of protein makes it ideal for providing structure to baked goods in situations where low protein flour is used.