Kimchi from Scratch
A chemist's take on Korea's greatest ferment. Exact salt ratios, gochugaru paste, and the immune science.
Chad Waldman
Analytical Chemist · April 15, 2026
Prep
30 min
Ferment
3–5 days
pH Target
4.0–4.5
Salt
~3%
Yield
1 quart
Kimchi is the ferment that humbles you. Sauerkraut is cabbage and salt. Kimchi is cabbage, salt, gochugaru, garlic, ginger, fish sauce, scallions, and time. The complexity comes from the ingredient interactions, not just the bacteria.
What makes kimchi different from sauerkraut is the paste. The gochugaru, garlic, and ginger create an environment that selects for specific Lactobacillus strains. A 2025 study (PMID: 41249184) used single-cell RNA sequencing to show that kimchi consumption upregulates MHC class II genes and enhances CD4+ T cell differentiation. Starter-culture kimchi showed stronger immune effects than spontaneously fermented kimchi.
That's a fancy way of saying: kimchi doesn't just taste good. At the molecular level, it's training your immune system.
What makes kimchi different from sauerkraut
Both are lacto-fermented cabbage. Both use salt to create anaerobic conditions. Both produce lactic acid. But the similarities end there.
Sauerkraut uses 2% salt by weight, dry-salted. Kimchi uses a 3% brine soak, then rinses, then adds a spice paste. The paste introduces sugars (which accelerate fermentation), garlic (antimicrobial against unwanted bacteria), and capsaicin from gochugaru (which may promote beneficial Lactobacillus growth).
The result: kimchi ferments faster (3–5 days vs 3–4 weeks), develops more complex flavors, and has a broader microbial profile.
Ingredients
- 1 lb napa cabbage (about half a head)
- 2 tbsp coarse sea salt (for salting stage)
- 3 tbsp gochugaru (Korean red pepper flakes — not cayenne)
- 2 tbsp fish sauce (or soy sauce for vegan)
- 1 tbsp sugar (feeds the bacteria)
- 4 cloves garlic, minced
- 1 inch fresh ginger, grated
- 3 scallions, cut into 1-inch pieces
Use our Salt Calculator for exact amounts. Check environment with the Lab Calculator.
Instructions
1Salt the cabbage
Cut napa cabbage into quarters, then 2-inch pieces. Toss with 2 tablespoons coarse salt per pound of cabbage. Let sit 2 hours, tossing every 30 minutes. The cabbage will wilt and release liquid. This is the dry-salt stage — it draws out water and begins the cell breakdown.
Chemist's note
Weigh your cabbage. 2 tablespoons per pound is approximately 3% salt by weight. Use our Salt Calculator to be exact.
2Rinse and drain
After 2 hours, rinse the cabbage 3 times under cold water to remove excess salt. Taste a piece — it should be pleasantly salty, not overwhelming. Drain thoroughly in a colander for 15–20 minutes.
Chemist's note
If it’s too salty after rinsing, the final kimchi will be too salty. Rinse again. You can always add salt later. You can’t remove it.
3Make the paste
Blend: 3 tablespoons gochugaru (Korean red pepper flakes), 2 tablespoons fish sauce, 1 tablespoon sugar, 4 cloves garlic (minced), 1 inch ginger (grated), 2 tablespoons water. This is the flavor engine. The sugar feeds the Lactobacillus. The garlic and ginger add antimicrobial compounds.
Chemist's note
Gochugaru is not the same as cayenne. It’s smoky, slightly sweet, and less sharp. This is non-negotiable for real kimchi flavor.
4Mix and pack
Toss the drained cabbage with the paste. Add sliced scallions and matchstick daikon if you have them. Wear gloves. Pack tightly into a quart jar, pressing down until liquid rises above the vegetables.
Chemist's note
Leave 1 inch of headspace. Kimchi produces a lot of CO2 in the first 3 days. If you seal it tight, it will overflow or the jar may crack.
5Ferment 3–5 days, then refrigerate
Leave at room temperature (65–75°F) for 3–5 days. Taste daily after day 2. When it’s tangy and slightly effervescent, move to the fridge. The pH should be 4.0–4.5. It will continue to slowly ferment in the fridge for months.
Chemist's note
Kimchi at day 3 is young and crisp. At week 2 it’s funky and complex. At month 3 it’s sour and perfect for kimchi jjigae. All stages are safe below pH 4.5.
The science
A 2025 study in npj Science of Food (PMID: 41249184) examined kimchi's immune effects at single-cell resolution. In 13 overweight adults over 12 weeks, kimchi upregulated MHC class II genes via the JAK/STAT1-CIITA axis, enhanced antigen uptake, and accelerated CD4+ T cell differentiation. Starter-culture kimchi showed stronger effects than spontaneously fermented.
A 2021 Cell study (PMID: 34256014) showed high-fermented-food diets increased gut microbiota diversity and decreased 19 inflammatory markers. Kimchi was one of the key fermented foods in the study.
Read more on our Science page.