Fermented Food OEM Development Guide | Product Development with Koji, Lactic Acid Bacteria & Enzymes

Kombucha, plant-based yogurt, amazake — fermented foods are a rapidly growing category in Japan, driven by the "gut health" boom and rising health consciousness. OEM products leveraging fermentation technology can create unique added value that other food categories cannot offer.

The most important knowledge in fermented food manufacturing is understanding the metabolic characteristics and optimal cultivation conditions of the microorganisms used. Each microorganism transforms raw materials through unique metabolic pathways, altering flavor, texture, nutritional value, and shelf life. In OEM development, the optimal microorganism must be selected according to the desired product characteristics.

Koji Mold (Aspergillus oryzae / A. sojae / A. luchuensis)

The filamentous fungus that underpins Japanese fermented foods, koji was designated as Japan's "National Mold" by the Brewing Society of Japan in 2006. Koji's defining characteristic is its powerful enzyme-producing capability. It secretes large quantities of amylase (starch breakdown), protease (protein breakdown), lipase (fat breakdown), and other enzymes, converting raw materials such as rice, soybeans, and wheat into sugars, amino acids, and fatty acids. Optimal cultivation temperature is 30–35°C at 90–95% humidity, and koji making (seikiku) requires 42–48 hours. A. oryzae is used for sake, miso, soy sauce, and amazake; A. luchuensis (black koji) is used for shochu, awamori, and citric acid fermentation. In recent years, koji amazake and shio koji (salt koji) — which leverage koji's enzymatic activity — have gained attention as health foods.

Lactic Acid Bacteria (Lactobacillus, Lactococcus, Streptococcus, etc.)

A general term for bacteria that convert sugars into lactic acid, they are involved in fermented foods worldwide — yogurt, cheese, pickles, kimchi, and sourdough bread. Lactic acid fermentation has two types: homofermentation (primarily producing lactic acid — the source of yogurt's tartness) and heterofermentation (producing lactic acid plus carbon dioxide and other compounds — contributing to pickle flavors). Optimal cultivation temperatures range widely from 20–45°C depending on the strain, with cultivation times of 6–48 hours. The pH reduction caused by lactic acid (pH 3.5–4.5) provides both preservation and distinctive sourness. For probiotic products, strain-level identification (e.g., L. rhamnosus GG, L. casei Shirota) is directly linked to product differentiation.

Yeast (Saccharomyces cerevisiae, etc.)

A fungus that converts sugars into ethanol and CO2 through alcoholic fermentation. It is essential in the production of bread, beer, wine, sake, and miso. Optimal cultivation temperature is 25–30°C; alcoholic fermentation occurs under anaerobic conditions, while aerobic conditions promote growth. In food OEM, fermented products with controlled alcohol production — such as non-alcoholic fermented beverages and natural yeast bread starters — are increasingly popular.

Acetic Acid Bacteria (Acetobacter / Gluconobacter) & Natto Bacteria (Bacillus subtilis var. natto)

Acetic acid bacteria are aerobic bacteria that oxidize ethanol to acetic acid, used in vinegar and kombucha production. Kombucha is produced by a symbiotic culture of acetic acid bacteria and yeast (SCOBY) and has been a rapidly growing product category in the health-conscious market. Natto bacteria are aerobic bacteria that form heat-resistant spores and break down soybean protein to produce nattokinase (a fibrinolytic enzyme) and vitamin K2.

The fermented food market has expanded beyond traditional miso, soy sauce, and pickles, with new product categories emphasizing health functionality growing rapidly. In OEM development, understanding market trends and identifying a differentiable positioning are the keys to success.

Kombucha

A lightly carbonated beverage made by fermenting tea (black or green) with added sugar using a SCOBY (Symbiotic Culture of Bacteria and Yeast). Japan's domestic kombucha market has been growing at 20–30% annually since 2023. The key manufacturing consideration is managing the degree of fermentation — over-fermentation increases acetic acid concentration and makes the product unpalatable. Typically, primary fermentation (7–14 days at 25–30°C) reduces sugar content from 8–12 Brix to 2–4 Brix, and secondary fermentation (in-bottle, 2–4 days) generates carbonation. Controlling the final alcohol content to below 1% is mandatory for selling as a soft drink under Japanese law (1% or above requires a liquor license). Flavored kombucha with fruit juice or herbs is popular, and in OEM production, a common approach is to add flavoring to an existing kombucha base.

Plant-Based Yogurt

Products made by fermenting plant-based milks — soy milk, almond milk, oat milk, coconut milk — with lactic acid bacteria. The market is growing on the back of dairy allergy accommodation and expanding vegan demand. The technical challenge is compensating for inferior texture (viscosity, smoothness) compared to dairy yogurt, which requires optimization of thickeners (pectin, tapioca starch) and stabilizers. Soy milk yogurt benefits from soy oligosaccharides that promote lactic acid bacteria growth, yielding relatively stable fermentation. OEM minimum lots are typically 1,000–3,000 units (100–400 g cups).

Fermented Pastes & Seasonings

OEM demand is increasing for seasonings leveraging fermentation technology — shio koji (salt koji), soy sauce koji, fermented chili paste (sambal, gochujang), and fermented butter. Shio koji in particular has maintained steady demand since its 2010s boom in Japan, and its simplicity (made from only rice koji, salt, and water) means even small-scale manufacturers can handle OEM production. Fermentation takes 7–10 days at room temperature, though manufacturing in a temperature-controlled fermentation room (25–30°C) is preferred for consistent quality.

Amazake

A traditional Japanese fermented beverage in which rice koji enzymes saccharify rice starch, known as "drinkable IV drip" for its recognized health benefits. Manufacturing centers on a saccharification process at 55–60°C for 8–12 hours with rice koji, rice, and water. It contains no alcohol and can be sold as a soft drink. Both straight-type (20%+ glucose content) and concentrated-type (requires 2x dilution) are available. Recent trends include fruit amazake and multigrain amazake, with ingredient variation being a key differentiator.

The quality of fermented foods is highly dependent on the precision of environmental parameter control during the fermentation process. Even with the same raw materials and the same microbial strain, inadequate control of temperature, pH, water activity, and oxygen supply can lead to batch-to-batch quality variation, off-flavor development, and in the worst case, spoilage or pathogen growth.

Temperature Control

Fermentation microorganisms have optimal growth temperatures, and deviations from this range cause reduced fermentation speed, changes in metabolite profiles, and dominance of contaminant organisms. Industrial fermentation equipment typically uses jacketed fermentation tanks (circulating hot/cold water through the outer wall for temperature control), with temperature accuracy of ±0.5°C as a standard control criterion. By fermented food type:

• Yogurt (lactic acid fermentation): 40–43°C for 4–6 hours. In co-cultivation of L. bulgaricus and S. thermophilus, if temperature drops below 40°C, S. thermophilus becomes dominant and acidity weakens.
• Miso (complex fermentation): Immediately after preparation, 25–30°C to promote yeast and lactic acid bacteria growth, followed by aging at 15–20°C for 6–12 months. Quick-method miso can be shortened to 3–6 months with heated aging at 30–35°C.
• Kombucha: 25–30°C for 7–14 days. Above 30°C, acetic acid bacteria become dominant and sourness intensifies.

pH Management

The single most important indicator for monitoring fermentation progress is pH. In lactic acid fermentation, the rate of pH decline indicates fermentation health. In yogurt production, the standard practice is to cool and halt fermentation when pH reaches 4.6. pH 4.6 is also the lower growth limit for Clostridium botulinum, making it a critical food safety threshold. Ideally, fermentation tanks should be equipped with in-line pH sensors for real-time monitoring. pH meter calibration should be performed daily before start of operations using pH 4.01 and pH 7.00 standard solutions.

Water Activity (Aw) Management

Water activity governs the growth potential of microorganisms, and each type of fermented food has an appropriate range. Miso (Aw 0.80–0.86), soy sauce moromi (Aw 0.78–0.82), pickles (Aw 0.90–0.97) — each product's water activity range is designed to allow growth of target microorganisms while suppressing growth of harmful ones. Water activity is controlled by adjusting salt and sugar concentrations, but excessive reduction also suppresses the target fermentation organisms, requiring balance optimization.

Oxygen Supply (Aerobic/Anaerobic Conditions)

Acetic acid fermentation and primary kombucha fermentation are conducted under aerobic conditions, while alcoholic and lactic acid fermentation perform optimally under anaerobic to micro-aerobic conditions. Tank sealing, headspace management, and nitrogen purging as needed — oxygen environment control determines the direction of fermentation.

The most important quality indicator for fermented foods, especially probiotic products, is viable cell count (CFU: Colony Forming Units). Claims like "contains 10 billion lactic acid bacteria" directly drive consumer purchase decisions, but maintaining those cell counts throughout the product lifecycle is a significant technical challenge.

CFU Measurement & Labeling

Viable cell counts are measured by the standard plate count method using agar media and expressed as CFU per gram (solid products) or per milliliter (liquid products). For yogurt, Japan's Fair Competition Code for Fermented Milk requires a lactic acid bacteria count of 10 million/ml or more to qualify as "fermented milk." For probiotic supplements, the international practice is to display guaranteed viable cell count at the end of shelf life, which means the cell count at manufacture must be 2–5 times the guaranteed value (overcharge). This accounts for die-off during storage, and since the rate varies by storage temperature, water activity, oxygen exposure, and coexisting components, formulation is designed based on accelerated stability testing data (3 months at 40°C, 75% relative humidity).

Probiotics vs. Prebiotics

• Probiotics: "Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host" (FAO/WHO definition). Lactobacillus and Bifidobacterium species are representative, with different health effects (digestive regulation, immune modulation, allergy relief, etc.) demonstrated in clinical research for each strain. The important point is that probiotic effects are strain-specific — different strains of the same species may have different effects.
• Prebiotics: "Substrates that are selectively utilized by host microorganisms, conferring a health benefit" (ISAPP definition). These include fructooligosaccharides (FOS), galactooligosaccharides (GOS), inulin, and resistant dextrin. They serve as "food" for probiotics, selectively promoting the growth of bifidobacteria and lactic acid bacteria in the gut.
• Synbiotics: Products combining probiotics and prebiotics for expected synergistic effects. In OEM products, "gut health" products combining lactic acid bacteria with dietary fiber are increasingly common.
• Postbiotics: Metabolites produced by microorganisms during fermentation (organic acids, short-chain fatty acids, peptides, polysaccharides, etc.) or heat-killed microbial cells. Since maintaining live cells is unnecessary, they offer superior product stability and are easy to distribute at room temperature. Products containing heat-killed lactic acid bacteria (e.g., EC-12 strain) market themselves with claims of "X trillion lactic acid bacteria."

The labeling and advertising of fermented foods in Japan must comply with the Food Labeling Act, Health Promotion Act, and Act against Unjustifiable Premiums and Misleading Representations. Particular care is required for cell count claims and health benefit assertions to avoid misleading consumers.

Labeling Rules under Japan's Food Labeling Act

Fermented foods require the same mandatory labeling as general processed foods (product name, ingredients, net contents, best-before date, storage instructions, manufacturer). A notable point specific to fermented foods is the order of ingredient listing. Raw materials used in fermentation (rice koji, lactic acid bacteria culture medium, SCOBY, etc.) are listed as ingredients, but the microorganisms themselves may be treated as either ingredients or food additives depending on the case. When lactic acid bacteria are used as a fermentation starter and remain in the final product, they are listed as ingredients; when used as a processing aid that is largely absent from the final product, labeling is not required.

Basis & Precautions for "X Billion Lactic Acid Bacteria" Claims

When displaying lactic acid bacteria content on a product, analytical data supporting that figure must be retained. When displaying viable cell counts, the most honest approach is to show the value guaranteed at the end of shelf life. For heat-killed lactic acid bacteria (pasteurized cells), the count is displayed as total cell count, but to prevent confusion with live cells, "heat-killed lactic acid bacteria" must be clearly stated. Under Japan's Act against Unjustifiable Premiums and Misleading Representations, cell count claims without supporting evidence risk being subject to a cease-and-desist order as "misleading representations of superiority." Retain third-party laboratory cell count measurement results (certificates of analysis) for each production lot.

Regulations on Health Benefit Claims

Claiming health benefits such as "boosts immunity," "improves gut health," or "promotes beautiful skin" for fermented foods may violate Japan's Act on Securing Quality, Efficacy and Safety of Products Including Pharmaceuticals and Medical Devices (Pharmaceutical and Medical Device Act). The range of claims permissible for foods is limited to expressions like "helps regulate digestive function" (approved FOSHU expression) or "helps maintain a favorable gut environment" (Food with Function Claims notification expression). Expressions implying disease prevention or treatment for unapproved/unnotified foods are illegal.

• FOSHU (Foods for Specified Health Uses): Requires individual review and approval by Japan's Consumer Affairs Agency. Review period: 2–3 years; cost: tens of millions of yen and up.
• Foods with Function Claims: A notification system to the Consumer Affairs Agency. Requires scientific evidence from clinical trials or systematic reviews. 2–3 months from notification to acceptance; cost: ¥1,000,000–5,000,000 (approx. $7,000–35,000).
• General foods: Health benefit claims are not permitted. However, nutrient content claims ("rich in dietary fiber," etc.) and claims based on nutrient reference values are allowed.

During OEM development, we strongly recommend conducting a legal review by an administrative scrivener or attorney specializing in Japan's Pharmaceutical and Medical Device Act and Act against Unjustifiable Premiums and Misleading Representations for package design and e-commerce product descriptions before product launch.

Fermented food OEM costs vary significantly depending on the duration and complexity of the fermentation process. Products with short fermentation (hours to days) and those requiring long aging (months to years) have fundamentally different cost structures, so category-specific understanding is essential.

Liquid Fermented Beverages (Kombucha, Amazake, Lactic Acid Bacteria Drinks)

• Minimum lot: 500 ml × 1,000 bottles and up
• Manufacturing cost per bottle: ¥300–600 (approx. $2–4)
• Breakdown: Ingredients ¥80–150, fermentation processing ¥50–100, bottle/cap/container ¥50–120, filling/sterilization ¥40–80, label/packaging ¥30–60, quality inspection (apportioned) ¥20–50
• Initial costs: Prototyping ¥50,000–150,000 (approx. $350–1,050), nutritional analysis ¥30,000–50,000 (approx. $210–350), label design/plate fee ¥50,000–150,000 (approx. $350–1,050)

Products like kombucha that generate carbonation through secondary fermentation require pressure-resistant bottles and gas pressure management, increasing container costs. Amazake does not involve alcoholic fermentation and can be manufactured under a soft drink manufacturing license.

Solid Fermented Foods (Miso, Shio Koji, Pickles)

• Minimum lot: Miso 500 g × 500 units and up; shio koji 200 g × 1,000 units and up
• Manufacturing cost: Miso 500 g approximately ¥250–500/unit (approx. $1.75–3.50); shio koji 200 g approximately ¥150–300/unit (approx. $1–2)
• Breakdown: Ingredients (for miso: soybeans, rice koji, salt) 30–40%, fermentation/aging management 20–30%, containers/packaging 15–25%, filling/inspection 10–15%

For miso OEM, the length of the aging period directly impacts cost. A 3-month quick-method miso and a 12-month naturally brewed miso differ by a factor of 4 in tank occupancy fees (storage costs). An approach worth considering is starting with quick-method production for the initial lot and transitioning to natural brewing once sales gain traction.

Plant-Based Yogurt & Fermented Desserts

• Minimum lot: 100–400 g cups × 1,000–3,000 units
• Manufacturing cost per unit: ¥80–200 (approx. $0.55–1.40)
• Breakdown: Plant-based milk ingredients ¥30–60, lactic acid bacteria/additives ¥10–30, fermentation/filling ¥20–40, container/lid ¥15–40, cold chain logistics ¥10–30

Since plant-based yogurt is a chilled product, cold chain (refrigerated logistics) costs are added at the distribution stage. Shelf life is 2–4 weeks after manufacture, making demand forecasting and production planning accuracy the key to preventing inventory loss.

Probiotic Supplements (Capsules, Granules, Tablets)

• Minimum lot: 30-count packages × 1,000–3,000 units
• Manufacturing cost per unit: ¥200–600 (approx. $1.40–4.20)
• Microbial powder ingredient costs account for 40–60% of costs, and licensing fees for specific strains may be added.

Selecting a fermented food OEM manufacturer in Japan requires evaluation along three axes: fermentation technology expertise, starter culture management systems, and quality control consistency. Because fermentation involves working with "living organisms," it demands unique management capabilities distinct from chemical processing.

Fermentation Equipment Evaluation Points

• Fermentation tank type and capacity: Stainless steel jacketed tanks (with temperature control) are standard, ranging in capacity from 100 L to 10,000 L. Confirm whether tanks of the appropriate size for your order volume are available. Small-lot production requires small tanks of 500 L or less.
• Temperature control precision: Verify whether the fermentation tanks maintain temperature control precision of ±0.5°C. Manufacturers with automated temperature logging systems (SCADA, etc.) offer higher process control reliability.
• CIP (Clean-In-Place) equipment: Availability of automated tank cleaning systems. These are essential for preventing residual microorganisms from previous batches (cross-contamination) during product changeovers. Manufacturers relying solely on manual cleaning require careful attention to cross-contamination risk management.
• Sterilization equipment: Verify whether raw material pre-sterilization (pasteurizer, UHT sterilizer) and final product sterilization equipment are in place. For products like kombucha that are not heat-sterilized, aseptic filling equipment or clean-room filling environments are required.

Starter Culture Management Verification

• Culture stock management: Verify the preservation method for microbial strains in use. Frozen storage (-80°C deep freezer) or freeze-dried storage is standard. To prevent strain degradation (performance decline from accumulated mutations) through repeated subculturing, manufacturers operating a master cell bank / working cell bank system are preferred.
• Strain identification & purity testing: Verify whether regular confirmation that the correct strain is being used (through scientific methods such as genetic analysis) is performed. Check whether contamination detection systems are in place.
• Custom strain handling: Verify whether the manufacturer can accept and manage client-specified strains (specific probiotic strains, etc.). For patented strains, also confirm whether the manufacturer can facilitate license agreement verification.

Quality Assurance & Track Record Verification

• HACCP certification / FSSC 22000: Verify hazard analysis implementation for fermented food manufacturing (biological hazards are especially critical). Check whether fermentation temperature, fermentation time, pH, and viable cell counts are properly managed as CCPs (Critical Control Points).
• Microbiological testing capability: Verify whether in-house laboratory testing (total viable count, coliform bacteria, fungal count, specific pathogens) is available. Manufacturers relying solely on external testing laboratories may face challenges with turnaround speed.
• Similar product track record: Confirm production experience in your target product category. Commissioning a miso manufacturer to produce plant-based yogurt versus a dairy manufacturer involves very different levels of technical suitability.
• Development support: If your organization lacks fermentation expertise, it is crucial whether the OEM manufacturer's engineers can support everything from formulation design to fermentation condition optimization. Select manufacturers with R&D departments capable of providing technical support from prototyping through scale-up to mass production.

Fermented food OEM requires precise management of temperature, pH, and water activity because it involves working with "living organisms" — microorganisms. On the other hand, fermentation technology enables the development of products with powerful differentiating factors such as health functionality and unique flavors. If you are considering entering growing categories like kombucha or plant-based yogurt, start by clarifying your product concept and consulting with a manufacturer that has the appropriate expertise.

This technology is ideal when:

• You want to develop fermented beverages in growing markets — kombucha, amazake, plant-based yogurt
• You want to create a seasoning brand with the added value of "fermentation" — shio koji, fermented condiments
• You want to expand into gut-health and wellness products leveraging probiotics
• You want to create original products leveraging traditional Japanese fermentation techniques (miso, pickles, etc.)

Key questions to ask your OEM manufacturer:

• Do you have production experience in my target fermented food category?
• What is your fermentation tank temperature control precision? Do you have automated logging systems?
• Is your starter culture preservation and management system (master cell bank, etc.) established?
• Can you perform in-house microbiological testing (viable cell count, coliform bacteria, pathogens)?
• Can your R&D department provide technical support from formulation design through fermentation condition optimization?

Our platform makes it easy to search and compare OEM manufacturers in Japan that specialize in fermentation technology. Start by browsing manufacturer detail pages and reach out for a free consultation.