Cheddar's taste is not the work of any single microbe. A 2023 study published in Nature Communications, led by bioengineer Ahmad Zeidan, shows that flavor emerges from a chain of interactions: Streptococcus thermophilus donates amino acids that a whole community of Lactococcus strains needs to grow, and competition within that community then keeps off-flavors in check. Remove one link, and the cheese changes.
The Microbial Architects of Cheddar Flavor
Cheesemakers have long known that certain bacterial species matter, but the community-level interactions that unfold as milk becomes cheese remained poorly understood. To crack that problem, Zeidan's team ran a year-long experiment using Cheddar as a model system. The choice was deliberate: Cheddar's starter culture contains roughly 25 to 30 bacterial strains, an intermediate level of microbial complexity that made the interactions tractable to study.
The researchers' approach was elegantly subtractive. Rather than adding microbes, they removed either a single strain or a group of strains from the starter culture and then assessed how each removal affected flavor development. This let them isolate the contribution of individual players within a crowded ecosystem — a bit like pulling one musician from an orchestra to hear exactly what part they were playing.
Streptococcus thermophilus: The Essential Amino Acid Donor
The clearest finding concerned Streptococcus thermophilus. Its presence proved essential for the growth of the Lactococcus population. Metatranscriptomic analysis and metabolic modeling of controlled milk fermentation experiments revealed why: S. thermophilus acts as a key amino acid donor to the Lactococcus community, alleviating nitrogen limitations that can arise during cheese ripening.
In other words, S. thermophilus is the community's supplier. Nitrogen is a building block bacteria cannot do without, and in the nutrient-tight environment of ripening curd, Lactococcus strains depend on this cross-feeding to stay metabolically active. The study also tied S. thermophilus to early metabolic changes during milk fermentation, including the complete consumption of lactose and the production of galactose — and concluded that both its early and late activity are critical to the long-term effect on the Lactococcus population and on flavor development.
Lactococcus Strains: Drivers of Flavor and Off-Flavor Prevention
If S. thermophilus is the supplier, Lactococcus strains are the flavor workforce. Their metabolic activity is what actually builds the taste of Cheddar, and the study reports that in the presence of S. thermophilus, the Lactococcus population enjoyed a significant growth benefit lasting a full year, producing a distinct final cheese metabolome profile.
But the community polices itself. Metatranscriptome analyses revealed that one Lactococcus cremoris strain made Cheddar taste good by limiting the formation of compounds that, in excess, lead to off-flavors. When the team looked closer, they found that competition between that L. cremoris strain and another Lactococcus strain drove the formation of these compounds. The desirable taste, in other words, comes not from harmony alone but from a managed rivalry — competition within the community acting as a brake on flavors that would otherwise spoil the party.
