Short answers, pulled from the story.
The main bacteria used to make yogurt are Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. Other lactobacilli and bifidobacteria are sometimes added during or after culturing, and plant-based versions use strains like Lactobacillus casei, Lactobacillus rhamnosus, and Bifidobacterium bifidum.
Yogurt was probably discovered by Neolithic people in Central Asia and Mesopotamia around 5000 BC, when the first milk-producing animals were domesticated. The earliest yogurts were likely fermented by wild bacteria inside goat skin bags.
Stamen Grigorov, a Bulgarian medical student in Geneva born in 1878, first examined the microflora of Bulgarian yogurt. In 1905 he described it as a spherical and a rod-like lactic acid-producing bacterium, and in 1907 the rod was named Bacillus bulgaricus.
Yogurt is made by warming milk to between 30 and 45 degrees Celsius, mixing in a starter culture of Streptococcus thermophilus and Lactobacillus bulgaricus, and keeping it warm for four to twelve hours. Higher temperatures ferment faster but risk a lumpy texture or whey separation.
Greek yogurt is the North American name for strained yogurt, which has been strained through a filter to remove the whey and give a much thicker consistency. In the Middle East strained yogurt is called labneh, and in Britain the name Greek may only be applied to yogurt made in Greece.
A 2011 review found high-quality clinical evidence insufficient to conclude that yogurt lowers disease risk, but later studies link it to improved lactose tolerance and digestion. Daily intake of 50 grams has been shown to reduce risk of overweight or obesity by 13 percent and type 2 diabetes by 7 percent.
Isaac Carasso founded Danone in Barcelona in 1919, and the brand later expanded to the United States as Dannon. Armenian immigrants Sarkis and Rose Colombosian started Colombo and Sons Creamery in Andover, Massachusetts, in 1929, and in 1966 invented fruit on the bottom yogurt, soon passing one million dollars in annual sales.