When you're enjoying your burrito, you should briefly think of the biochemical ingenuity of the horse-riding culture that nearly overran Europe. The Mongols had to process their food in a special way, and they liked getting drunk — this led to a culinary treasure.
The Mongols tended to eat what they brought with them, and what they brought with them was horses. Horses, like all mammals, produced both meat and milk. Milk would have been very useful, but much of the Mongol population was lactose intolerant. Rather than cutting off half their food supply, the Mongols found a way to use it.
Although they couldn't eat mare's milk as it was, they did drink kumis, a very slightly alcoholic drink made from milk. Here is how you make it: first you take mare's milk, and add two types of bacteria, named Streptococcus lactis and Leuconostoc citrovorum. After the bacteria thicken the milk a little bit, you let the milk go through a second fermentation stage, during which the milk turns alcoholic. During the first stage, the lactose in the milk is neatly dismantled. Lactose is a fairly complicated molecule (C12H22O11), so breaking it up into two molecules of lactic acid that makes it easier to digest. The kumis and the curdled milk were both less likely than milk to spoil on long journeys in hot climates.
As the Mongols spread across Asia, they took the kumis with them. Many different people came into contact with them, especially when they were at the peak of their empire. Among those people, it seems that the Russians were the ones that enjoyed kumis the most. They repeated the process with the milk from local livestock, which happened to be cows instead of horses. As they weren't as pressed for time as the Mongols — or as they had alternate sources of alcohol — instead of turning it alcoholic, they let it thicken longer. The slightly-sour taste and creamy texture of the thickened milk caught on. It spread across Europe,and into parts beyond, even though the Mongols did not. So when you enjoy dip, or creme fraiche, or even buttermilk (which is made with the same kind of bacteria and closely resembles the first stage of kumis-making), thank the Mongols for bringing the gift of deliciousness.
Top Image: Liz West.