pH drops as lactobacilli consume sugars and produce lactic acid
Lacto-fermentation begins when salt-tolerant lactobacteria (primarily Lactobacillus species) present on the vegetable surface consume sugars and produce lactic acid as a metabolic byproduct. This drives pH downward from neutral (6.5-7.0) toward acidic (3.0-4.0) over a 2-4 week fermentation. The acidic environment preserves the vegetables and inhibits pathogenic bacteria that prefer neutral pH.
The lactobacteria population explodes early in fermentation as they colonize the anaerobic, salty environment. Salt (typically 2-5% by weight of vegetables) creates osmotic stress that suppresses mold and spoilage organisms while allowing salt-tolerant lactobacteria to thrive. The high initial population growth creates rapid acid production in the first week, then the rate slows as the population stabilizes and acidity itself limits further growth.
Fermentation stages reflect bacterial succession and flavor development
Week 1: pH drops steeply (6.5 to 5.0) as lactobacteria population peaks. The ferment becomes noticeably sour and cloudy (bacteria are dividing rapidly). Week 2-3: pH continues dropping more slowly (5.0 to 3.5) as the bacterial population plateaus. Flavors develop as bacteria produce secondary metabolites. Week 4+: pH stabilizes around 3.0-3.5. The ferment tastes fully sour and has developed funk and umami from bacterial metabolism. Cold storage slows fermentation and extends freshness; room temperature fermentation will eventually reach a stable endpoint and remain preserved indefinitely.