Grain and milk are awkward foods on their own. Few hunter-gatherers eat raw cereal grain; the majority of adult humans are naturally lactose intolerant. Fermentation brings microorganisms into the picture and solves both problems at once: it converts starch in grain to sugar and sugar to alcohol; it breaks most of the lactose in milk down into other compounds, and turns liquid milk into portable, storable cheese.

The earliest evidence for beer is, surprisingly, Anatolian: chemical analysis of large stone basins at Göbekli Tepe has detected oxalate residues — almost certainly from a cereal-based fermented drink, probably brewed for large ritual gatherings. Beer was not a by-product of agriculture but perhaps one of its motivations: grain for beer made sense even before grain for bread.

The oldest hard evidence for cheese comes from perforated clay sieves containing milk-fat residues, found in Poland and dated to around 5500 BCE; in the Near East, layers at Çatalhöyük are older still. The sieve's function is the same as the cheesecloth used today: to separate solid casein from liquid whey. Turning milk into a low-lactose, portable cheese multiplied the returns from livestock long before lactose tolerance spread in adult Europeans — thousands of years earlier, a partnership with microbes closed that gap.