What You Need to Know
The high salt concentration suppresses spoilage microbes while lactic acid bacteria ferment lactose to lactic acid, lowering the pH to 4.5–4.8. This acidification triggers proteolysis of casein, releasing flavor peptides and creating feta's characteristic tangy flavor. Salt also draws out whey, reduces water activity to ~0.85, and stabilizes the curd structure.
The Science
Primary Reaction
Fermentation of lactose by lactic acid bacteria to lactic acid, leading to proteolysis of casein.