Every cheese you've ever loved began as the same three raw materials: lactose, protein, and fat. What separates a nutty Swiss from a piquant Pecorino isn't the milk alone—it's which of three biochemical pathways the cheesemaker chooses to emphasize. Scientists studying cheese flavor describe glycolysis (the breakdown of lactose), proteolysis (the breakdown of protein), and lipolysis (the breakdown of fat) as the engines of flavor formation, and understanding them lets you deconstruct any wedge into its scientific origins.
The Foundation of Flavor: Milk's Core Components
Milk arrives at the creamery carrying the entire flavor potential of the finished cheese, packed into three components. Lactose and citrate are the main carbohydrates in all mammalian milks, though lactose content varies widely from animal to animal. Proteins and fats make up the rest of the raw material that microbes and enzymes will spend weeks or years dismantling. As biosolutions producer Novonesis explains, starter and ripening cultures produce volatile compounds by metabolizing lactose, protein, and fat, while enzymes drive those same conversions, releasing lactic acid, peptides, amino acids, and fatty acids that become the characteristic flavors and aromas of cheese. The regional conditions, technology, and ripening environment all shape how this plays out—which is why the same pathways can taste wildly different depending on where and how they're steered.
Glycolysis: Lactose's Transformation into Tang and Acidity
The first pathway is the sprinter of the trio. Lactose is metabolized into L-lactate, DL-lactate, or a racemic mixture of both—a conversion that a scientific review of cheese flavor pathways calls essential to flavor production in all cheeses. This is the tangy backbone of nearly every variety. But the story doesn't end with lactic acid. In cheddar and Dutch-type cheeses, nonstarter bacteria isomerize the L-lactate produced by the Lactococcus lactis starter into DL-lactate, subtly shifting the acid profile. Some bacteria, including Leuconostoc species, produce other compounds such as ethanol alongside lactate.
The most theatrical example lives in the Alps. In Swiss cheese, Propionibacterium species metabolize lactate into propionates, acetates, carbon dioxide, and water—and that carbon dioxide is the cause of the characteristic "eyes" in the cheese. Acetate, meanwhile, is an important flavor compound in many cheeses, forming not only from lactose but also via lactate and citrate metabolism. So glycolysis gives you both the tang and, in the right hands, the holes.
