The Core of the Difference: Lactose
Milk's inherent sweetness comes from a naturally occurring disaccharide sugar called lactose. Composed of two simpler sugars, glucose and galactose, lactose makes up about 5% of milk's content and provides energy. For the body to digest lactose, an enzyme called lactase is required to break it down. While most mammals produce high levels of lactase only during infancy, a significant portion of the human population maintains lactase production into adulthood. However, in cheesemaking, the fate of this lactose takes a dramatic turn, explaining why the final product is so low in sugar.
The Cheesemaking Process: A Sugar-Removing Journey
Cheesemaking is an ancient form of food preservation that relies on a series of microbial and mechanical steps to transform a liquid food into a solid one with a much longer shelf life. The reduction of lactose is central to this transformation.
Step 1: Acidification with Starter Cultures
The process begins with the addition of a 'starter culture'—specific strains of lactic acid bacteria (LAB)—to the milk. These bacteria begin consuming the lactose in the milk and converting it into lactic acid. This fermentation process causes the milk's acidity to increase, which is a critical step in preserving the cheese and influencing its final flavor and texture.
Step 2: Separation of Curds and Whey
Once the milk has reached the desired acidity, rennet, an enzyme that causes the milk protein casein to coagulate, is added. This forms a solid gel, which is then cut into smaller pieces. The liquid that separates from these solids is called whey. Since lactose is water-soluble, the vast majority of it moves into the whey, leaving the curds (the future cheese) with significantly less sugar than the original milk.
Step 3: Draining and Pressing
After the curds and whey are separated, the cheesemaker drains off the liquid whey. For many hard cheeses, the curds are further heated, cut, and pressed to expel even more moisture (and thus more whey and lactose). This pressing step is a physical process that further concentrates the protein and fat while leaving more of the water-soluble lactose behind.
The Aging Process: The Final Sugar Purge
The final, and often most important, stage for flavor development and sugar removal is aging, also known as ripening. The longer a cheese is aged, the more time the bacteria within the curd have to continue breaking down any remaining lactose. This microbial activity is responsible for creating the complex, robust flavors found in aged cheeses like sharp cheddar or Parmesan. In aged, hard cheeses, the lactose content becomes so low that the cheese is effectively sugar-free. This is why many people who are lactose intolerant can enjoy aged cheeses without digestive issues.
Comparison: Milk vs. Aged Cheddar
To illustrate the dramatic nutritional difference, consider a comparison of the key components per 100 grams:
| Nutrient | Whole Milk | Aged Cheddar Cheese |
|---|---|---|
| Sugar (Lactose) | ~4.99 g | ~0.48 g |
| Carbohydrates | 4.99 g | 3.09 g |
| Protein | ~3 g | ~23 g |
| Fat | ~1 g | ~33 g |
Why Different Cheeses Have Different Sugar Levels
Not all cheeses are created equal when it comes to sugar content. The length of the aging process is the primary factor. Fresh, soft cheeses like ricotta or cottage cheese, which retain more whey and are not aged, will have higher lactose levels than a well-aged Parmesan. The longer the cheese is aged, the more opportunities the lactic acid bacteria have to consume any remaining sugar, resulting in a drier, harder, and lower-sugar product.
The Bottom Line: Health Implications
Understanding why cheese is low in sugar has important health implications, particularly for those with lactose intolerance. While consuming milk can cause digestive upset, the low-lactose content of aged cheeses means they are often a well-tolerated source of calcium and protein. The process showcases how a single raw material can be transformed into a wide array of products with drastically different nutritional profiles, all through the marvel of microbial fermentation.
Conclusion
In summary, the reason cheese has no sugar but milk does is a two-part process involving chemistry and microbiology. First, the lactose-rich whey is drained away from the milk solids (curds). Second, the lactic acid bacteria introduced during cheesemaking consume any remaining lactose through fermentation. The longer the cheese is aged, the more thoroughly this process completes, leading to the near-zero sugar content found in hard, mature cheeses. This natural transformation highlights the incredible power of fermentation in altering food's composition and nutritional properties, turning a sugar-rich liquid into a low-sugar, high-protein solid.
