Fermentation is how humans preserved food for thousands of years before refrigeration. It's also how some of the world's most flavourful and nutritious foods are made — kimchi, miso, sourdough, kombucha, kefir, sauerkraut, pickles, beer, wine, vinegar.
The principle is simple: beneficial microbes — bacteria and yeast — transform sugar and starch into acid, alcohol, or gas. This preserves the food, creates complex flavours, and produces compounds that support gut health.
You don't need specialist equipment. You don't need training. You need a jar, a culture, and patience.
## The Three Types of Fermentation
All food fermentation falls into three categories, distinguished by the dominant microorganism:
### Lacto-Fermentation
Lactobacillus bacteria convert sugars into lactic acid. This is the process behind sauerkraut, kimchi, pickles, and fermented hot sauce. The lactic acid preserves the food and creates a tangy, complex flavour.
Lacto-fermentation is the simplest to start with. Vegetables + salt + time. No special culture needed — the bacteria are naturally present on vegetable surfaces.
### Acetic Fermentation
Acetobacter bacteria convert alcohol into acetic acid. This is how vinegar is made. In kombucha, a SCOBY (symbiotic culture of bacteria and yeast) first converts sugar into alcohol, then converts the alcohol into acetic acid — producing a tangy, slightly effervescent drink.
### Alcoholic Fermentation
Yeasts convert sugar into alcohol and CO2. This is how beer, wine, and mead are made. It's also the first stage of kombucha and kefir production.
Most home fermentation involves one or more of these processes. Understanding which one you're working with helps you troubleshoot when things don't go as expected.
## What You Need to Start
### Essential Equipment
**A glass jar.** Wide-mouth, 1–2 litres. Glass is non-reactive and easy to clean. Avoid metal containers — acid corrodes them.
**An airlock lid.** Allows CO2 to escape without letting oxygen in. Critical for lacto-fermentation and kombucha. Without an airlock, you need to burp the jar daily to release pressure.
**Weights.** Stainless steel or glass weights keep vegetables submerged below the brine. Vegetables exposed to air develop mould.
**Salt.** Non-iodised sea salt or kosher salt. Iodine kills beneficial bacteria.
**A culture (for kombucha and kefir).** A SCOBY for kombucha, kefir grains for milk or water kefir. These are living colonies that self-replicate — one purchase provides an ongoing supply.
### Optional but Useful
- pH strips to measure acidity (useful for troubleshooting) - A fermentation crock for larger batches - A fine-mesh strainer for separating grains from liquid
## Your First Ferment: Sauerkraut
Sauerkraut is the best first ferment. It requires only cabbage and salt. No culture, no special equipment, no experience.
### Ingredients
- 1 medium head of green cabbage (approximately 1 kg) - 15g non-iodised sea salt (approximately 1 tablespoon)
### Method
**Step 1: Prepare the cabbage.** Remove outer leaves (save one). Quarter the cabbage, remove the core, and shred finely.
**Step 2: Salt and massage.** Place shredded cabbage in a large bowl. Sprinkle with salt. Massage firmly for 10 minutes. The salt draws water from the cabbage, creating its own brine. You'll see liquid pooling at the bottom of the bowl.
**Step 3: Pack the jar.** Transfer cabbage and brine to a clean glass jar. Pack tightly, pressing down with your fist to eliminate air pockets. The brine should cover the cabbage. If it doesn't, add a small amount of salt water (1 tablespoon salt per 500ml water).
**Step 4: Weigh and seal.** Place a weight on top to keep cabbage submerged. Cover with an airlock lid or a clean cloth secured with a rubber band.
**Step 5: Ferment.** Leave at room temperature (18–22°C) for 1–4 weeks. Taste every few days. After 1 week, it's lightly tangy. After 3–4 weeks, it's fully sour. Refrigerate when it reaches your preferred flavour.
### What to Expect
- **Days 1–3:** Little visible change. The salt is drawing out moisture. - **Days 3–7:** Bubbles appear. The brine becomes cloudy. This is lacto-fermentation in action — CO2 is a by-product. - **Weeks 1–4:** Flavour deepens. Taste regularly. When it's sour enough for you, it's done.
White film on the surface: This is kahm yeast — harmless but flavoursome. Skim it off. It's not mould. Mould is fuzzy and coloured (green, black, white fuzzy). Kahm yeast is a thin, flat, white film.
## Your Second Ferment: Kombucha
Kombucha requires a SCOBY — a symbiotic culture of bacteria and yeast that looks like a translucent, rubbery disc. The SCOBY converts sweet tea into a tangy, slightly effervescent drink.
### Ingredients
- 1 SCOBY with starter tea (approximately 200ml) - 1 litre filtered water - 4–6 bags of black or green tea - 100g white sugar
### Method
**Step 1: Brew the tea.** Boil water. Steep tea bags for 10 minutes. Remove bags. Dissolve sugar while hot. Cool to room temperature (hot liquid kills the SCOBY).
**Step 2: Add the SCOBY.** Pour cooled tea into a clean glass jar. Add the SCOBY and starter tea. Cover with a cloth and rubber band (the culture needs airflow but must be protected from insects).
**Step 3: Ferment.** Leave at room temperature for 7–14 days. The SCOBY will sink, float, or sit at an angle — all normal. After 3–5 days, a new SCOBY layer begins forming on the surface.
**Step 4: Taste and bottle.** After 7 days, taste with a straw. If it's too sweet, leave longer. If it's tangy enough, remove the SCOBY (and 200ml of liquid as starter tea for your next batch), and bottle the rest.
**Step 5: Second ferment (optional).** Add fruit juice, ginger, or herbs to the bottle and seal for 2–3 days at room temperature. This creates natural carbonation. Refrigerate to stop fermentation.
### What to Expect
- The SCOBY produces a baby SCOBY with each batch. One SCOBY becomes two, then four. Share them with friends. - Kombucha tastes different from batch to batch. Temperature, tea type, sugar amount, and fermentation time all affect flavour. - A vinegary taste means it fermented too long. Shorten the time next batch.
## Your Third Ferment: Milk Kefir
Milk kefir uses kefir grains — small, cauliflower-like colonies of bacteria and yeast that ferment milk into a thick, tangy, probiotic-rich drink.
### Ingredients
- 2 tablespoons milk kefir grains - 500ml whole milk (unpasteurised is ideal; pasteurised works)
### Method
**Step 1: Combine.** Add kefir grains to a clean glass jar. Pour milk over them.
**Step 2: Ferment.** Cover with a cloth. Leave at room temperature for 18–24 hours.
**Step 3: Strain.** Pour through a non-metal strainer (plastic or nylon). The grains stay in the strainer. The liquid is your kefir.
**Step 4: Repeat.** Return the grains to the jar and add fresh milk. The grains are self-sustaining — they'll keep fermenting indefinitely.
### What to Expect
- After 24 hours, milk should be thickened and tangy. If it's still thin, leave longer. - Over-fermented kefir separates into curds and whey. This isn't ruined — blend it or use the whey in smoothies. - Kefir grains grow. You'll have more than you need within weeks. Give excess to friends or add to smoothies.
## Troubleshooting
**Mould:** If you see fuzzy growth (green, black, pink, or white fuzzy), discard the entire batch and start over. Clean the jar with boiling water. Mould means something wasn't submerged or the environment wasn't clean enough.
**Smell:** Fermented food smells tangy, sour, or yeasty — not rotten. If it smells putrid, something has gone wrong. Discard.
**No bubbles:** Bubbles are a sign of active fermentation. No bubbles after 3 days may mean the temperature is too low (move to a warmer spot) or the culture is inactive (for kombucha and kefir, ensure the culture is fresh).
**Too salty:** Use less salt next batch. You can dilute an overly salty sauerkraut by adding more shredded unsalted cabbage.
## The Regenerative Case for Fermentation
Fermentation is regenerative in the truest sense: you start with simple ingredients and living cultures, and you grow food. Not manufacture it. Grow it.
One kombucha SCOBY produces kombucha indefinitely. One set of kefir grains ferments milk endlessly. One batch of sauerkraut cabbage produces seeds for the next crop. The cultures self-replicate, the waste is minimal, and the output is living food with no packaging, no processing, and no industrial supply chain.
For a home practising bokashi composting, fermentation completes a regenerative circuit: food scraps become soil, soil grows vegetables, vegetables become fermented food, food scraps start the cycle again.
## The Grown. Fermentation Kit
If you want to start fermenting without assembling equipment from scratch, the [Grown. Fermentation Kit](/products/fermentation-kit) includes:
- **1L glass fermentation jar** with airlock lid for controlled fermentation - **Stainless steel weights** to keep vegetables submerged in brine - **SCOBY + starter tea** for your first batch of kombucha
Glass and stainless steel. No plastic. Live cultures lab-tested for viability.
For a seasonal approach to fermentation — along with composting, growing, and other regenerative practices — the [Grown. Home Box](/products/seasonal-kit) delivers a curated quarterly kit built around what's in season.
## A Final Note
Fermentation isn't difficult. It's unfamiliar. Once you've made your first batch of sauerkraut, you'll understand the process intuitively. After that, you'll wonder why you ever bought sauerkraut in a jar.
The barrier isn't skill. It's starting. Start with cabbage and salt. The rest follows.