Preservation & Ripening Technique

Fermenting

Q: How do I know if my fermentation was successful?

Three indicators: (1) CO2 bubbles are visible in the first 24-72 hours (gassing). (2) The brine becomes slightly cloudy. (3) The smell is sour and pleasant, comparable to yoghurt or sauerkraut. Measurement: pH below 4.6 is the objective proof of successful lacto-fermentation. (Sandor Katz, The Art of Fermentation, Chelsea Green, 2012)

Q: Which salt should I use for fermentation?

Non-iodised salt. Iodised salt contains potassium iodide that inhibits bacterial growth, including the desired Lactobacillus. Use: Celtic sea salt, Himalayan salt, non-iodised table salt or kosher salt. Amount: 2-3% of vegetable weight for lacto-fermentation of vegetables.

Q: Is fermentation safe in the professional kitchen?

Yes, when correctly executed. Properly executed lacto-fermentation reaches pH 3.5-4.5, preventing Clostridium botulinum and most pathogens from growing. HACCP requirements: document pH monitoring per batch, record start and end dates, destroy batches where final pH exceeds 4.6. (EU Regulation 852/2004; FDA Bacteriological Analytical Manual)

Q: What is koji and how do I use it?

Koji (Aspergillus oryzae) is a mould that produces enzymes which break down proteins into amino acids (umami). Basic application: shio koji (rice + koji + salt + water, 1-2 weeks at 28°C) as a marinade or flavour enhancer. Advanced: garum from fish or meat trimmings via koji at 60°C/4-8 weeks. Purchase dried koji or koji spores from specialist suppliers. (Rene Redzepi & David Zilber, Noma Guide to Fermentation, 2018)

Q: Why does the pH drop during fermentation?

Lactobacillus bacteria convert sugars (glucose, fructose) anaerobically into lactic acid (C3H6O3). Lactic acid is a weak acid that releases H+ ions in water, causing the pH to drop. From an initial value of approximately 6.5 (fresh vegetables) you reach 3.5-4.5 after complete fermentation. The pH drop is both the preservation mechanism and the flavour foundation of all sour fermented products.

Q: What is the difference between kimchi and sauerkraut?

Both are lacto-fermented vegetables. Sauerkraut: white cabbage + salt (2%), started aerobically, fermented anaerobically. Neutral sourness, mild flavour. Kimchi: napa cabbage + gochugaru (chilli) + garlic + ginger + (optional) fish sauce. Richer flavour profile due to additional ingredients. Final pH values are comparable (3.5-4.0). Ripening time at room temperature: sauerkraut 2-8 weeks, kimchi 1-4 weeks + post-ripening under refrigeration.

The oldest preservation technique in the world: micro-organisms transform sugars into acids, alcohol and complex flavour compounds. From kimchi and sauerkraut to miso and garum: fermentation is back in the professional kitchen as a value creation strategy.

2-3% optimal salt percentage for lacto-fermentation of vegetables (Sandor Katz, 2012)

3.5-4.5 pH after successful lacto-fermentation (safety zone)

20-22°C optimal room temperature for lacto-fermentation

4.6 critical pH threshold: above this level, Clostridium botulinum growth is possible

Requirements

Fermentation vessel or glass jar (airtight or with airlock) Precision scale (for accurate salt percentage measurement) Thermometer (room and product temperature) pH indicator strips or pH meter Fermentation log (date, batch, weight, salt%, pH, temperature)

In brief

[DEFINITION] Fermentation

Fermentation is a microbiological conversion process in which sugars are transformed by bacteria, yeasts or moulds into acids, alcohol, CO2 or other compounds. This lowers the pH, inhibits pathogenic micro-organisms and creates complex flavour profiles. Fermentation is one of the oldest and safest preservation techniques, when correctly executed. (FAO/WHO, Health and Nutritional Properties of Probiotics in Food, 2006)

Lacto-fermentation (lactic acid fermentation): Lactobacillus bacteria convert sugars into lactic acid. pH drops from 6.5 to 3.5-4.5. Sauerkraut, pickles, kimchi, yoghurt, kefir. Most widely applied in the professional kitchen. Anaerobic: no oxygen. Salt keeps pathogens at bay while lactobacilli thrive. (Sandor Katz, The Art of Fermentation, 2012)
Alcoholic fermentation: Saccharomyces cerevisiae (baker's yeast) converts sugars into ethanol + CO2. The basis of sourdough bread, beer, wine, sake, mirin. Sourdough combines yeast and bacterial fermentation: lactic acid + acetic acid + CO2 for leavening.
Acetic acid fermentation (acetobacter): an aerobic process in which ethanol is converted into acetic acid. The basis of cider vinegar, rice vinegar, balsamic vinegar and kombucha. Kombucha: a SCOBY (Symbiotic Culture of Bacteria and Yeast) ferments sweetened tea.
Koji fermentation (mould fermentation): Aspergillus oryzae or Aspergillus sojae produce protease, amylase and lipase enzymes that break down proteins and carbohydrates into amino acids (umami). The basis of miso, soy sauce, sake, amazake, tempeh. Modern application: "garum" from fish, meat or vegetables via koji. Fermentation times: 3 weeks (shiro miso) to 3 years (hatcho miso). (Rene Redzepi & David Zilber, The Noma Guide to Fermentation, Artisan 2018)

Four fermentation types

Lacto-fermentation

Lactobacillus converts sugars into lactic acid. Anaerobic. Salt 2-3% of product weight. Temperature 18-22°C. Result: low pH (3.5-4.5), long shelf life, complex sour flavour.

Examples: Sauerkraut, kimchi, pickles, yoghurt, kefir, miso (combined)

Alcoholic fermentation

Yeasts convert sugars into ethanol + CO2. The basis of sourdough (combined with lacto-fermentation), sake, mirin. Temperature: 18-25°C for sourdough. Timing: 8-72 hours per cycle.

Examples: Sourdough bread, sake, mirin, beer, wine

Acetic acid fermentation

Aerobic: acetobacter converts ethanol into acetic acid. Requires oxygen. The basis of all vinegar types and kombucha. Result: high acidity, strongly preserving.

Examples: Cider vinegar, rice vinegar, balsamic vinegar, kombucha

Koji / mould fermentation

Aspergillus oryzae enzymes break down proteins into umami-rich amino acids. Modern garum revival in fine dining. Fermentation times ranging from weeks to years.

Examples: Miso, soy sauce, sake, garum, amazake, shio koji

Sources: Sandor Katz (2012); Rene Redzepi & David Zilber (2018); FAO/WHO (2006)

Fermented products in the professional kitchen

Kimchi

Korean lacto-fermented napa cabbage with gochugaru, garlic and ginger. pH 3.5-4.0 after 1-4 weeks. Active lactobacilli. Refrigerate once desired ripeness is reached.

Type: lacto pH: 3.5-4.0 Temp: 18-22°C

Sauerkraut

White cabbage, 2% salt (by weight), anaerobic fermentation. Industrial: 4-8 weeks. Artisanal: 2-4 weeks at 18-22°C. pH 3.5-4.5 at ripeness. Vitamin C content increases during fermentation.

Type: lacto Salt: 2% Duration: 2-8 weeks

Miso

Koji (A. oryzae) on rice or barley combined with soybeans + salt. Ripening time: 3 weeks (shiro miso, sweet) to 3 years (hatcho miso, intense). Base ingredient for dashi-based sauces.

Type: koji Duration: 3 weeks-3 years

Garum

Modern reinterpretation: fish, meat or vegetable garum via koji enzymes at 60°C for 4-8 weeks. Noma popularised beef garum and mushroom garum. Intense umami in small quantities.

Type: koji + enzymatic Temp: 60°C

Sourdough

Wild yeast (Saccharomyces + Kazachstania) + lactobacilli in wheat flour-water starter. Feed daily. Proofing times: 8-16 hours cold (refrigerator) or 3-6 hours warm (25°C). pH of ripe sourdough: 3.5-4.5.

Type: combination pH: 3.5-4.5

Kombucha

SCOBY (Symbiotic Culture of Bacteria and Yeast) ferments sweetened tea. Phase 1: yeast converts sugar into ethanol. Phase 2: acetobacter converts ethanol into acetic acid. End product: <0.5% alcohol, pH 2.5-3.5.

Type: dual pH: 2.5-3.5 Duration: 7-14 days

Fermentation always requires pH monitoring. Check pH after the first 48-72 hours. If pH has not dropped below 5.0 within 3 days (for lacto): assess the batch by smell and consider restarting with fresh starter or a higher salt concentration.

Step-by-step method

1

Select and wash the vegetables

Use fresh, undamaged vegetables. Damaged tissue increases the risk of unwanted micro-organisms. Wash thoroughly in accordance with EU 852/2004. Cut or grate to the desired thickness. Weigh the final vegetable weight precisely for correct salt calculation.

HACCP: use only clean equipment and containers. Glass or food-safe plastic (no metal: salt corrodes).
2

Weigh salt precisely (2-3%)

Weigh 2-3% salt based on vegetable weight. Example: 1,000 g cabbage = 20-30 g salt (non-iodised). Iodised salt can inhibit fermentation due to the antimicrobial action of iodine. Use Celtic sea salt, Himalayan salt or non-iodised table salt. (Sandor Katz, The Art of Fermentation, 2012)

Below 1.5% salt: fermentation proceeds quickly but is less stable. Above 3.5%: fermentation is slower and the end product saltier.
3

Mix and massage

Mix vegetables and salt. Massage or knead for 5-10 minutes. The salt draws moisture from the vegetable cells via osmosis: this is the brine that submerges the vegetables. Sufficient brine is crucial: an anaerobic environment prevents oxidation and mould growth.
4

Pack and submerge

Pack the vegetables tightly into a glass jar or fermentation vessel. Press down so the brine rises above the vegetables. Remove air bubbles. Place a weight (stone or fermentation weight) to keep everything submerged. Vegetables above the brine surface may develop mould (surface mould is not dangerous but unpleasant).
5

Start fermentation (18-22°C)

Seal the jar but not completely airtight (CO2 must be able to escape). An airlock is ideal. Store at 18-22°C out of direct sunlight. First 24-48 hours: CO2 bubbles become visible (sign that fermentation has started). The brine may become slightly cloudy: this is normal.

Monitor daily for mould growth (surface) or foul odour (rot). If the brine is slimy and smells strongly unpleasant: discard the batch.
6

Measure pH after 48-72 hours

Measure the pH of the brine after 48-72 hours. Target: pH must have dropped below 5.0 as a sign of active lacto-fermentation. Target end value: 3.5-4.5. pH above 5.0 after 3 days: check salt percentage, temperature and cleanliness of the vessel. Log each measurement: date, batch number, pH value, temperature.

HACCP critical point: pH above 4.6 after completed fermentation leaves the risk of Clostridium botulinum open. In anaerobic fermentation with insufficient acid: botulism is theoretically possible. In practice, correctly executed lacto-fermentation (pH < 4.6) is inherently safe.
7

Ripen and store cold

After 3-14 days (depending on vegetable, temperature and desired flavour profile) the fermentation is complete. Refrigerate (< 4°C) to virtually halt the fermentation. Flavour continues to develop under refrigeration but very slowly. Shelf life: cold-fermented vegetables 3-6 months provided they remain submerged in brine. Label each batch: product, start date, pH, salt%, chef.

HACCP: pH monitoring and botulism risk

Clostridium botulinum and the pH threshold of 4.6

Clostridium botulinum produces the most potent biological toxin known (botulinum toxin). Its spores are anaerobic and can survive in preserved and fermented products. The critical safety threshold: at pH below 4.6, C. botulinum cannot grow or produce toxin. (FDA Bacteriological Analytical Manual)
Correctly executed lacto-fermentation reaches pH 3.5-4.5 and is therefore inherently safe. Risk arises with insufficient salt percentage, too high a temperature or insufficient ripening time, preventing the pH from dropping.
HACCP requirement for the professional kitchen: pH monitoring per fermentation batch is mandatory. Document date, batch number, starting pH, pH after 48h, final pH. Destroy batches where the final pH exceeds 4.6.

Source: FDA Bacteriological Analytical Manual; EU Regulation 852/2004

Surface mould versus spoilage

White kahm yeast (Kahm yeast, e.g. Pichia and Candida species) on the fermentation surface is unpleasant but not dangerous. Remove the layer and ensure vegetables are submerged below the brine again.
Coloured mould (green, black, pink): these are pathogenic moulds that can produce mycotoxins. Discard the batch. Cause: vegetables above the brine surface, too low a salt concentration or contamination via dirty equipment.
Smell is the most reliable indicator: properly fermented products smell sour and pleasant. A strong putrid or meaty odour indicates unwanted bacterial growth.

Source: Sandor Katz — The Art of Fermentation (2012); RIVM — Fermentation and food safety

Lacto-fermentation: salt, temperature and ripening time

Product	Salt percentage	Temperature	Ripening time	Target pH
Sauerkraut	2.0-2.5% of cabbage weight	18-22°C	2-8 weeks	3.5-4.5
Kimchi	2.0-3.0% total	18-22°C (start), then cold	1-4 weeks + post-ripening	3.5-4.0
Fermented pickle	2.5-3.5% brine solution	18-22°C	3-7 days	3.5-4.0
Lacto-fermented vegetables (general)	2-3% of vegetable weight	20-22°C	3-14 days	3.5-4.5
Shio koji (salt rice)	10% salt by rice weight	28-35°C (for koji growth)	48-72 hours koji + 1-2 wk ripening	n/a

Source: Sandor Katz — The Art of Fermentation (Chelsea Green, 2012); FAO/WHO Probiotics in Food (2006)

Food cost: value creation from inexpensive raw materials

Kimchi from inexpensive cabbage varieties: Napa cabbage (€0.60-1.20/kg) + small amounts of gochugaru, garlic, ginger. Fermentation costs: energy (room temperature) + labour (30 min preparation). One kilogram of kimchi after fermentation: market value €6-12 per kg as a side dish or €15-25 as a specialty product. ROI: 5-15x on raw materials. (Market prices 2024)
Garum from meat or fish trimmings: Trimmings from fish, meat or mushrooms that would otherwise go to stock are transformed via koji into an umami-rich liquid. Noma's beef garum uses minced beef (€4-8/kg). The end product is a flavour enhancer for which restaurants pay a premium. Transform waste into value.
Sourdough as an alternative to purchased bread: A living sourdough starter costs virtually nothing (flour + water + time). Compared to commercial yeast: cheaper per use at large volumes. Bread made from sourdough has a higher perceived value than standard yeast bread and justifies a higher menu price per unit.
Fermentation and shelf life: Fermented vegetables (kimchi, pickles, sauerkraut) have a shelf life of 3-6 months when stored correctly. This significantly reduces food waste compared to fresh vegetables (3-7 days). For a restaurant with daily purchasing, a fermentation programme can structurally reduce the waste percentage.

Frequently asked questions

How do I know if my fermentation was successful?

Three indicators: (1) CO2 bubbles are visible in the first 24-72 hours (gassing). (2) The brine becomes slightly cloudy. (3) The smell is sour and pleasant, comparable to yoghurt or sauerkraut. Measurement: pH below 4.6 is the objective proof of successful lacto-fermentation. (Sandor Katz, The Art of Fermentation, Chelsea Green, 2012)

Which salt should I use for fermentation?

Non-iodised salt. Iodised salt contains potassium iodide that inhibits bacterial growth, including the desired Lactobacillus. Use: Celtic sea salt, Himalayan salt, non-iodised table salt or kosher salt. Amount: 2-3% of vegetable weight for lacto-fermentation of vegetables.

Is fermentation safe in the professional kitchen?

Yes, when correctly executed. Properly executed lacto-fermentation reaches pH 3.5-4.5, preventing Clostridium botulinum and most pathogens from growing. HACCP requirements: document pH monitoring per batch, record start and end dates, destroy batches where final pH exceeds 4.6. (EU Regulation 852/2004; FDA Bacteriological Analytical Manual)

What is koji and how do I use it?

Koji (Aspergillus oryzae) is a mould that produces enzymes which break down proteins into amino acids (umami). Basic application: shio koji (rice + koji + salt + water, 1-2 weeks at 28°C) as a marinade or flavour enhancer. Advanced: garum from fish or meat trimmings via koji at 60°C/4-8 weeks. Purchase dried koji or koji spores from specialist suppliers. (Rene Redzepi & David Zilber, Noma Guide to Fermentation, 2018)

Why does the pH drop during fermentation?

Lactobacillus bacteria convert sugars (glucose, fructose) anaerobically into lactic acid (C3H6O3). Lactic acid is a weak acid that releases H+ ions in water, causing the pH to drop. From an initial value of approximately 6.5 (fresh vegetables) you reach 3.5-4.5 after complete fermentation. The pH drop is both the preservation mechanism and the flavour foundation of all sour fermented products.

What is the difference between kimchi and sauerkraut?

Both are lacto-fermented vegetables. Sauerkraut: white cabbage + salt (2%), started aerobically, fermented anaerobically. Neutral sourness, mild flavour. Kimchi: napa cabbage + gochugaru (chilli) + garlic + ginger + (optional) fish sauce. Richer flavour profile due to additional ingredients. Final pH values are comparable (3.5-4.0). Ripening time at room temperature: sauerkraut 2-8 weeks, kimchi 1-4 weeks + post-ripening under refrigeration.

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Applying the techniques described requires professional expertise and training. KitchenNmbrs is not liable for damage, injury, illness or loss resulting from the application of information from this website without adequate professional guidance or verification. Every kitchen, every product and every environment is different: always apply your own professional judgement.

Food safety & HACCP

The HACCP guidelines, temperatures and storage advice on this page are based on Codex Alimentarius (WHO/FAO) as the global baseline standard and EU Regulation 852/2004. Local laws and regulations may differ. Always consult your national food safety authority for the applicable standards in your region:

Netherlands: NVWA (nvwa.nl)
Belgium: FAVV (favv-afsca.be)
Germany: BfR (bfr.bund.de)
United Kingdom: FSA (food.gov.uk)
United States: FDA (fda.gov) — FDA Food Code
EU general: EU Regulation (EC) 852/2004 on food hygiene
International: Codex Alimentarius CAC/RCP 1-1969 (revised 2020)

Allergens & dietary information

Allergen information is indicative. When in doubt about allergens in preparations, always contact the supplier or a certified allergological adviser. KitchenNmbrs accepts no liability for allergic reactions or diet-related harm.

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Sources and legal information

Sandor Katz — The Art of Fermentation (Chelsea Green Publishing, 2012)
Rene Redzepi & David Zilber — The Noma Guide to Fermentation (Artisan, 2018)
Harold McGee — On Food and Cooking (Scribner, 2004) — micro-organisms and pH
FAO/WHO — Health and Nutritional Properties of Probiotics in Food (FAO Food and Nutrition Paper 85, 2006)
EU Regulation 852/2004 — food hygiene (fermentation as traditional preservation)
FDA Bacteriological Analytical Manual — Clostridium botulinum, Chapter 17