pH management — monitoring and interpreting the pH progression during fermentation — is the most important technical skill in fermentation work. The pH of a fermentation tells you what the bacteria are doing, whether the fermentation is proceeding normally, and whether any contamination has occurred. The Noma Guide's systematic pH documentation is one of its most significant contributions to home fermentation practice.
**The pH progression in lacto-fermentation:** - Day 1: pH 6.0–7.0 (neutral — the substrate's natural pH) - Day 3–5: pH 5.0–5.5 (Leuconostoc has established; acidity increasing) - Day 7–10: pH 4.0–4.5 (Lactobacillus has taken over; active acidification) - Day 14+: pH 3.5–4.0 (fermentation complete; stable; Lactobacillus-dominated) **Safety thresholds:** - pH below 4.6: Clostridium botulinum (the botulism organism) cannot survive. This is the critical safety threshold for lacto-fermented vegetables. - pH below 4.0: Most pathogenic organisms are inhibited. The fermentation is stable and safe. **The stuck fermentation signal:** pH that stops falling before reaching 4.5 indicates the fermentation has stalled — usually from insufficient salt, insufficient initial bacteria, or contamination. The solution: additional salt and time, or restart.
Noma Fermentation