Microbial Succession

A vegetable ferment is not one microbe doing one job — it is a relay. Different organisms dominate at different points along a falling-pH gradient, each handing off to the next as the brine they create becomes too acidic for them and just right for their successor. Understanding the curve tells you what is normal at day 3 versus day 30, and why a cool ferment is slower but cleaner.

Who shows up when

The succession is driven by acid tolerance: as pH drops, the field of organisms that can grow narrows. Three rough phases:

Phase	Days (at 18–22 °C)	Dominant organism	What it does	Brine pH
1 — Initiation	0–3	Mixed enterobacteria, wild flora	Consume oxygen, produce some CO₂; harmless at this stage	6.0 → 5.0
2 — Heterofermentative	2–7	Leuconostoc mesenteroides	Lactic + acetic acid + CO₂; sets anaerobic conditions, builds aroma	5.0 → 4.0
3 — Homofermentative	7–30+	Lactiplantibacillus plantarum, L. brevis	Drive pH to floor on clean lactic acid; finish the ferment	4.0 → 3.4

The early enterobacteria are out-competed the moment acid and CO₂ accumulate; they cannot tolerate the conditions their successors create. Leuconostoc self-limits near pH 4.5–4.0. Lactiplantibacillus plantarum, the most acid-tolerant of the group, has the last word and sets the finished pH of 3.4–3.6 for kraut.

Info

Each organism engineers the environment for the next. Leuconostoc’s CO₂ blanket purges oxygen (favoring anaerobes over surface yeasts), and its acid lowers pH into L. plantarum’s comfort zone. This is why you do not inoculate a healthy kraut — the cabbage already carries the whole relay team.

How temperature shifts the curve

Temperature does not change who runs the relay so much as how fast and in what proportion. Warmer ferments race; cooler ferments stroll.

Temperature	Pace	Character
18–22 °C / 64–72 °F	Balanced (the sweet spot)	Full Leuconostoc phase, complex flavor, low spoilage risk
22–27 °C / 72–80 °F	Fast	Leuconostoc phase compressed; L. plantarum dominates early; flatter, sharper flavor; higher kahm/mold risk
<18 °C / <64 °F	Slow	Longer, Leuconostoc-rich phase; rounder flavor; cleanest, but takes weeks longer

Note

Cooler is cleaner because the slow, acid-producing relay stays ahead of opportunistic spoilage organisms (surface yeasts, molds) the whole way down. Warm ferments can finish in days, but the compressed Leuconostoc phase gives a one-dimensional sour, and the warm, oxygen-rich early window favors kahm yeast. Many traditional krauts run a full month at ~18 °C for exactly this reason.

Concrete timeline

At 18 °C, expect bubbling (CO₂) by day 2–3, a clearly sour smell and pH near 4.0 by week one, and a finished pH of 3.4–3.6 by week three to four. The same cabbage at 25 °C might hit pH 4.0 in three days and “finish” in a week — faster, but with less of the Leuconostoc aromatic complexity.

Caution

The first 48 hours sit above pH 4.6 while oxygen is still being purged — the one window where pathogens are not yet excluded by acid. Keep vegetables submerged and at fermenting temperature (not warm, not in cold storage) so the LAB relay establishes acid quickly. See aerobic vs anaerobic. Source: NCHFP — Fermenting.

See also

• Lactic fermentation — the acid-producing chemistry behind the curve.
• Time and temperature — choosing a ferment temperature and schedule.
• Ferment predictor calculator — estimate timing from temperature and salt.