泡菜, Sauerkraut and Kimchi.
Kimchi a few days old is fizzy and fresh; a few weeks old, sharply sour and ready for stew. Different bacteria were in charge.
A vegetable ferment is not one fermentation but a relay. In the first days, Leuconostoc species — tolerant of salt and cold, not of much acid — dominate: they make lactic acid, acetic acid and carbon dioxide, giving young sauerkraut and kimchi their fizz and mild, fresh sourness. As the acid builds, they give way to Lactobacillus species, which tolerate more acid and push the pH lower, making the ferment sharper. Cool temperatures lengthen the first stage and give a gentler, more complex result; warm ones rush to sourness and risk softening.
Traditions shape the relay. German sauerkraut is shredded cabbage in its own brine at about 2 %, three to six weeks at cellar temperature. Korean kimchi salts napa cabbage, then adds a paste of chilli, garlic, ginger, fish sauce or salted shrimp, and ferments cold, often in the ground or a kimchi fridge. Sichuan 泡菜 uses whole vegetables in a 5–8 % brine with spices and Sichuan pepper, in a water-sealed 泡菜坛, and keeps the old brine (老盐水) going for years, topping up salt and vegetables, so each batch starts with a vigorous culture. The workshop follows the relay.
Below: the two populations over days at the temperature you choose — Leuconostoc first, then Lactobacillus as the pH falls (a teaching succession model) — and the days to "young" and "mature" sourness.
- Describe the succession in vegetable ferments.
- Explain how temperature changes the result.
- Compare sauerkraut, kimchi and 泡菜.
- Use an old brine as a starter.
A relay of bacteria
At 18 °C the ferment reaches a young, fizzy sourness in about 2.2 days and mature sharpness in about 3.1 in this model; at 6 °C, the kimchi-fridge temperature, young takes about 22 days and mature takes weeks longer, and at 24 °C young comes in 1.5. Starting from an old brine at 18 °C brings young to about 1.4 days and mature to 1.9, because the Lactobacillus are already in charge — which is why a Sichuan 泡菜 jar makes quick pickles (跳水泡菜) in a day or two.
Choose by taste. For fresh, lively kimchi, ferment a day or two at room temperature, then refrigerate; for 泡菜 to eat crisp, keep the brine strong and the jar cool; for sour cabbage to cook with (酸菜鱼, choucroute), let it go to maturity. Keep the water seal of a 泡菜坛 topped up so air stays out; skim any white film of kahm yeast from the surface (harmless but off-tasting), and discard anything with fuzzy, coloured mould or a rotten smell (XIV.10).
Make a small jar of quick kimchi or 泡菜 and taste a piece every day for two weeks, noting when it is fizzy and fresh and when it turns sharp. Move it to the fridge at the point you like best.
Terms
- Succession
- A sequence of microbes, each changing conditions for the next.
- Leuconostoc
- Early lactic bacteria: gassy, mild, cold-tolerant.
- 老盐水
- An old 泡菜 brine kept going for years as a starter.
- Kahm yeast
- A harmless white film yeast on ferment surfaces.
Sources
- USDA Complete Guide to Home Canning (2015), Guide 6, "Preparing and canning fermented foods and pickled vegetables": sauerkraut with 3 tablespoons of canning salt per 5 lb of cabbage (about 2.25 % by weight); ferments in 3–4 weeks at 21–24 °C or 5–6 weeks at 15–21 °C; above about 24 °C it may soften, below about 15 °C it may not ferment.
- A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
- H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.