Fermentation Scale-Up for Fermented Foods and Drinks: From Bench to Plant

What fermentation scale-up involves

Fermentation scale-up is the work of moving a fermented food or drink from flasks to pilot vessels and then to production tanks while the culture stays active, the product stays safe and each lot tastes the same. It rests on three things: building enough healthy inoculum through a seed train, controlling pH, temperature, oxygen and hygiene in much larger vessels, and choosing how the vessel runs (batch, fed-batch or continuous).^[1]

Scaling is not simply making more. A culture that behaves well in a one-litre flask meets different mixing, heat and oxygen conditions at 10,000 litres. This guide covers the physics, the seed train, vessel control, operating modes, the US safety route, finishing and viability, for yoghurt, kefir, kombucha, fermented vegetables and similar products. It sits after the Stanford fermented food study explainer in this series and before the pillar on formulating live-culture fermented foods.

Why fermentation scale-up is hard

Geometry works against you. In geometrically similar vessels, surface area per unit volume falls with the cube root of volume, so a 10,000 L vessel has only about 4.6% of the surface-to-volume ratio of a 1 L flask (Figure 1, FRL calculation). Jacket area per litre falls, so metabolic heat is harder to remove; surface gas exchange per litre drops; and mixing takes longer. Gradients in temperature, pH and dissolved oxygen appear that a small flask never showed, and they can change growth, acid profile and flavour.

That is why scale-up starts with knowing what changes, not with a bigger tank. A review of food fermentation notes that defined starter cultures and a controlled fermentation give more consistent quality;^[1] at larger scale, that control has to be engineered into the vessel and the process. For non-fermented products, FRL’s worked example on scaling a recipe from kitchen to pilot plant covers the batching side.

From bench to pilot to plant

A staged process keeps risk small. Bench work fixes the recipe and the critical parameters; the pilot tests them in production-like equipment; plant runs confirm consistency across lots. Small scale-down runs that mimic the gradients of a large vessel let teams find failure modes cheaply. USDA-led kombucha work shows why parameters must be defined first: tea type, inoculum age, the presence of a solid culture and the culture’s interfacial surface area all affected sugars, acids, alcohol, microbial counts and sensory quality.^[2] Early formulation matters too, because it sets the sugar, protein and buffering the culture meets at scale, and the matrix affects how well cultures survive.^[4] FRL’s guide to functional food development from R&D to manufacturing covers pilot production and transfer more broadly.

Source: FRL summary of standard practice.

Inoculum and seed-train development

Inoculum development builds enough active, pure culture to start the production vessel. Assuming a 5% v/v inoculum at every step, a 10,000 L batch needs 500 L of seed, which needs 25 L, which needs 1.25 L of starter culture: three transfers and an 8,000-fold increase in volume (Figure 2, FRL calculation). Each transfer should happen at a defined culture age and be checked for purity and cell count, since inoculum age shaped outcomes in the kombucha study.^[2] A banked, well-characterised starter culture removes variability at the first step, and mixed cultures such as kefir grains or a kombucha SCOBY need seed stages that preserve their balance of species. Many dairy and vegetable ferments use direct-vat-set starter cultures instead, which shortens or removes the seed train but moves the control point to the culture supplier’s specification and the cold chain.

Controlling the fermentation vessel

A fermentation vessel, whether a stainless tank for yoghurt or a vessel for kombucha, is a control system for the culture’s environment. In fermented food production, sensors and set-points come from bench data and are confirmed at pilot scale.

Source: FRL summary of standard bioprocess practice; see ^[1].

pH, temperature and dissolved oxygen

pH matters because acid production is both the product and a safety barrier in many fermented foods, and the pH end point often decides when a batch is finished. Temperature sets growth rate and the balance of flavour compounds. Oxygen separates aerobic steps, such as the acetic acid bacteria in kombucha, from largely anaerobic lactic acid fermentations, so the oxygen strategy must be chosen on purpose.^[3] In kombucha, sugar level, time and temperature also drive acids and alcohol content,^[3] which matters for the US alcohol limit discussed below.

Batch, fed-batch and continuous fermentation

The choice depends on the product, culture stability and risk appetite. Most fermentation processes still run as batch or fed-batch,^[1] and most fermented foods and drinks are made in batches because lots are easy to trace and the end point is set by pH or time. Fed-batch operation, where feed is added during the run, suits cultures stressed by high starting sugar. Continuous operation feeds and harvests steadily; it is promoted for its lower water, energy and labour use, but it suits only cases where volume and culture stability justify the extra control.^[1]

Source: FRL summary; see ^[1].

Sanitation, CIP and the US safety route

Contamination risk grows with surface area, hold time and the number of transfers. Hygienic vessel design, clean-in-place (CIP) cycles and validated cleaning keep unwanted microbes out, while culture-friendly conditions keep the starter ahead. In the US, a facility that must register with FDA generally needs a written food safety plan under 21 CFR Part 117, with a hazard analysis and risk-based preventive controls, which can include sanitation controls.^[10]

Classification decides which process rules apply. Acidified food under 21 CFR 114 means a low-acid food to which acid is added, with a finished equilibrium pH of 4.6 or below and water activity above 0.85; fermented foods are excluded from that definition.^[9] FDA’s precursor questions add three points for shelf-stable products: refrigerated foods fall outside Parts 113 and 114; a fermented food with a finished equilibrium pH of 4.6 or below is outside both (voluntary filing is possible); and a fermented food above pH 4.6 with water activity above 0.85 is a low-acid food under Part 113.^[7][8]

Kombucha deserves a special note: TTB rules apply if alcohol reaches 0.5% by volume at any point in production, at bottling or after bottling through continued fermentation in the bottle.^[11] Longer holds and larger, warmer vessels make that limit easier to cross, so alcohol testing belongs in the scale-up plan; the cluster’s US rules for fermented foods and drinks covers labelling. In the EU, operators work under Regulation (EC) No 852/2004 with hygiene procedures based on HACCP principles.^[12] Whichever route applies, keep the CIP record, fermentation end point and pH log in the safety file.

Formulator’s note. Clean the vessel, not the culture. Caustic or acid residues from CIP can inhibit a starter at the next fill, so confirm rinse-out (for example by pH or conductivity) and check counts on the first batch after a clean.

Downstream processing and finishing

Downstream processing decides how much of what fermentation built reaches the consumer. Options include filtration, centrifugation, pasteurisation, blending, carbonation and filling. Each step that kills or removes cultures changes what you can say on pack: a pasteurised kombucha is a fermented drink, not a live-culture one. Fermented is not the same as probiotic, either: the USDA-led kombucha study identified no known probiotic bacteria in its kombucha.^[2] The product matrix also changes survival; in one study, probiotic counts fell less in fermented milk than in an oat-based drink under simulated digestion.^[4] FRL’s natural flavoured kombucha project covers processing and stability for that category.

Keeping cultures viable at scale

Viability is the thread through every step above. Track it with plate counts or other viability methods at each scale, set acceptable ranges for culture age and count at transfer, and compare the end-of-fermentation count with the product’s target at the end of shelf life. Fermented foods are systems of microbial communities and metabolites,^[5] so pair counts with chemical markers such as pH, titratable acidity and, for kombucha, alcohol. Check the regulatory status of each microbial ingredient before scale-up; FDA publishes a partial list of microorganisms and microbial-derived ingredients used in food, which is a starting point, not an approval list.^[6] Reliable production at 10,000 L is built from this data, not from the recipe alone. For counting methods and label wording, see FRL’s explainer on CFU meaning in probiotics, and for a worked survival study, the cluster’s live-culture survival trial.

For brands & formulators

Planning to take a fermented food or drink from bench to commercial volume? FRL’s pilot plant R&D and scaling team runs small-batch pilot production and prepares SOPs, batch records and technology-transfer packs; commercial production runs through our network of partner manufacturers. Our Microbiome Solutions team defines culture, count and shelf-life targets, and viability and microbiological testing are run or arranged through accredited partner laboratories. Our new food product development and regulatory and scientific research teams settle the formula and the US process route.

• Scale-up plan: seed train, set-points, end point and in-process checks.
• Pilot batches with viability, pH and (for kombucha) alcohol data at each stage.
• Process classification against 21 CFR 113, 114 and 117 before you commit to a format.

Plan your pilot run or contact us with your product brief.

In this series

Fermented foods and live cultures (US): the study path.

• Stanford fermented food study explained: what the Cell 2021 trial showed and what it does not.
• Fermentation scale-up for foods and drinks (You are here): seed trains, vessel control and keeping cultures viable from bench to plant.
• Formulating live-culture fermented foods (pillar): strain, dose, matrix and survival.
• US rules for fermented foods and drinks: alcohol limits, labelling and claims.
• Live-culture survival trial in a fermented beverage: a worked example of CFU and pH through shelf life.
• Fermented foods and drinks FAQ: formulation, regulation and shelf-life questions answered.
• Service: Microbiome Solutions.

1. Siddiqui, S. A., Erol, Z., Rugji, J., Taşçı, F., Kahraman, H. A., Toppi, V., Musa, L., Di Giacinto, G., Bahmid, N. A., Mehdizadeh, M., & Castro-Muñoz, R. (2023). An overview of fermentation in the food industry: Looking back from a new perspective. Bioresources and Bioprocessing, 10, 85. https://doi.org/10.1186/s40643-023-00702-y (cited for defined starter cultures giving more controlled, consistent fermentation, for most processes running as batch or fed-batch, and for the case made for continuous operation).
2. Chaluvadi, S., Hotchkiss, A. T., Smith, B., McVaugh, B., White, A. K., Guron, G. K. P., Renye, J. A., & Yam, K. L. (2024). Key kombucha process parameters for optimal bioactive compounds and flavor quality. Fermentation, 10(12), 605. https://doi.org/10.3390/fermentation10120605 (USDA ARS record: publication 419117) (cited for tea type, inoculum age, solid inoculum and surface area affecting chemistry, counts and sensory quality, and for no known probiotic bacteria identified).
3. de Miranda, J. F., Ruiz, L. F., Silva, C. B., Uekane, T. M., Silva, K. A., Gonzalez, A. G. M., Fernandes, F. F., & Lima, A. R. (2022). Kombucha: A review of substrates, regulations, composition, and biological properties. Journal of Food Science, 87(2), 503–527. https://doi.org/10.1111/1750-3841.16029 (cited for the bacteria and yeast in kombucha and for sugar, time and temperature driving acids and alcohol content).
4. Pawlos, M., Szajnar, K., & Znamirowska-Piotrowska, A. (2024). Probiotic milk and oat beverages with increased protein content: Survival of probiotic bacteria under simulated in vitro digestion conditions. Nutrients, 16(21), 3673. https://doi.org/10.3390/nu16213673 (cited for the matrix effect on probiotic survival: larger losses in the oat-based than the milk-based product).
5. Park, I., & Mannaa, M. (2025). Fermented foods as functional systems: Microbial communities and metabolites influencing gut health and systemic outcomes. Foods, 14(13), 2292. https://doi.org/10.3390/foods14132292 (cited for fermented foods as systems of microbial communities and metabolites).
6. U.S. Food and Drug Administration. (n.d.). Microorganisms & microbial-derived ingredients used in food (partial list). https://www.fda.gov/food/generally-recognized-safe-gras/microorganisms-microbial-derived-ingredients-used-food-partial-list (cited for checking the status of microbial ingredients).
7. U.S. Food and Drug Administration. (n.d.). LACF/AF: Precursor questions and flow. https://www.fda.gov/media/89861/download (cited for refrigerated foods and fermented foods at pH 4.6 or below being outside 21 CFR 113/114, voluntary filing, and fermented foods above pH 4.6 and aw 0.85 being low-acid foods).
8. U.S. Food and Drug Administration. (2024). Compliance program 7303.070: Acidified and low-acid canned foods program, import and domestic (implemented 26 September 2024). https://www.fda.gov/media/182173/download (cited for FDA’s inspection programme for acidified and low-acid canned foods).
9. Code of Federal Regulations. (2026). Title 21, §114.3 Definitions (acidified foods). eCFR. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-114/subpart-A/section-114.3 (cited for the acidified food definition, pH 4.6 and aw 0.85, and the exclusion of fermented foods).
10. Code of Federal Regulations. (2026). Title 21, Part 117: Current good manufacturing practice, hazard analysis, and risk-based preventive controls for human food. eCFR. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-B/part-117 (cited for the food safety plan, hazard analysis and preventive controls, including sanitation controls).
11. Alcohol and Tobacco Tax and Trade Bureau. (2019). Kombucha. TTB. https://www.ttb.gov/regulated-commodities/beverage-alcohol/kombucha (cited for TTB rules applying when kombucha reaches 0.5% alcohol by volume at any time, including after bottling).
12. European Parliament and Council. (2004). Regulation (EC) No 852/2004 on the hygiene of foodstuffs. Official Journal of the European Union, L 139, 1–54. https://eur-lex.europa.eu/eli/reg/2004/852/oj (cited for EU hygiene procedures based on HACCP principles).