What You Need to Know
During fermentation lactose is metabolised by Lactobacillus helveticus and L. plantarum into lactic acid, while yeasts such as Kluyveromyces marxianus convert residual sugars into ethanol and CO₂. The resulting lactic acid lowers the pH to ~4.2, giving the beverage its mildly sour taste, while the CO₂ provides gentle carbonation. The simultaneous production of ethanol (~1‑2 % v/v) and lactic acid stabilises the microbial community and imparts a characteristic aroma.
The Science
Primary Reaction
lactose → lactic acid + ethanol + CO₂