Exploding Fermentation: What It Is, Why It Happens, and How to Prevent It

Fermentation remains one of the oldest and most reliable methods of food preservation. It has always relied on observation and restraint. Today, those same principles are measured through defined parameters and documented under modern food safety systems. It depends on controlled microbial activity that transforms sugars into acids, gases, and alcohols. When properly managed, this process lowers water activity, stabilizes food, and develops characteristic flavor and texture. When mismanaged, particularly in enclosed or pressure-retaining systems, that same microbial activity can become hazardous. The result is known as exploding fermentation, a preventable but potentially dangerous failure in both process control and regulatory compliance.

What Is Exploding Fermentation?

Exploding fermentation occurs when carbon dioxide (CO₂) produced by bacteria or yeasts accumulates faster than it can escape. If venting is restricted, internal pressure increases until the vessel or closure fails. This can occur in glass jars, sealed bottles, plastic tubs, stainless steel tanks, or bulk totes.

In traditional open-vessel fermentations, CO₂ is naturally released through diffusion. In modern sealed systems, venting and headspace are engineered controls that must be specified within the process design and documented within the facility’s HACCP or Food Safety Plan.

Fermentation is a biological control step that directly impacts product safety and container integrity. When pressure, pH, or microbial stabilization determine safety outcomes, fermentation must be classified and monitored as a Critical Control Point (CCP, a step where control is applied to prevent or eliminate a food safety hazard) under 9 CFR 417 or a Process Preventive Control under 21 CFR 117.

How and Why It Happens

Fermentation involves microbial metabolism that varies by temperature, substrate, and strain. As microbes consume carbohydrates, they generate acids, ethanol, and CO₂. Without a controlled outlet for this gas, pressure may exceed the tolerance of the container.

Common contributing factors include:

• Containers sealed before fermentation reaches a stable pH or terminal gravity (the point where sugars have been fully converted and fermentation has slowed)

• Rapid temperature shifts that accelerate microbial metabolism (often above 30 °C / 86 °F)

• Inadequate headspace, typically less than 5 - 10 percent of vessel volume

• Use of non-rated containers such as household glass jars or lightweight plastics

• Secondary fermentation triggered by residual sugars after packaging

For reference, one mole of glucose yields approximately two moles of CO₂ during fermentation (a mole is a unit chemists use to count molecules; one mole of CO₂ equals about 44 grams of gas). In sealed beverage production, this equates to roughly 2.5 to 3.5 volumes of CO₂, meaning the gas volume is 2.5 - 3.5 times the liquid volume, which can generate pressures exceeding 30 psi (approximately 2 bar) in a glass bottle not designed for carbonation.

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Fermentation is both a biological art and a technical system. The difference between flavor and failure lies in control.

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Hazards and Regulatory Implications

Exploding fermentation poses multiple hazards:

• Physical injury from shattered glass or metal fragments

• Chemical exposure if caustic cleaning agents or acids are nearby

• Product contamination in ready-to-eat or acidified food zones

• Oxygen displacement from large-scale CO₂ release in confined production areas

From a regulatory standpoint, uncontrolled fermentation can trigger findings under:

• 9 CFR 417 (HACCP): Failure to maintain process control at a critical step

• 21 CFR 117 (Preventive Controls): Inadequate monitoring or verification of fermentation parameters

• 21 CFR 110 (GMPs): Improper equipment suitability, maintenance, or container integrity

Facilities operating under inspection or registration must demonstrate that fermentation controls are measurable, repeatable, and defensible during regulatory audit or EIAO review.

Where It Appears Most Often

Exploding fermentation can occur in any sealed system containing live cultures. High-risk categories include:

• Beverages: kombucha, cider, beer, mead, kefir

• Vegetables: kimchi, sauerkraut, pickled vegetables under brine

• Meats: fermented or dry-cured sausages under unstable temperature or humidity

• Dairy: yogurt, cultured butter, cheese ripening environments

Producers expanding from small-batch to larger operations face increased risk if vessel design and monitoring systems do not scale proportionally to their operations.

Preventive Controls

Preventive controls are proactive measures built into a system to manage predictable hazards before they occur. Exploding fermentation is prevented through structured system design, validation, and documentation.

Controls include:

• Venting Systems: Use airlocks, blow-off tubes, or one-way valves designed to relieve pressure at or below 2 psi for small vessels or per manufacturer specification for tanks.

• Temperature and pH Monitoring: Maintain stable fermentation ranges, typically between 18 °C and 25 °C (64 - 77 °F), with continuous or daily logged readings.

• Headspace Management: Leave a minimum of 10 percent vessel volume unfilled to accommodate gas expansion and foam.

• Controlled Bottling: Package only once CO₂ production has stabilized, verified by consistent specific gravity or pH readings across 48 hours.

• Pressure-Rated Containers: Use glass rated for carbonation (>4 bar, approximately 60 psi) or stainless steel vessels fitted with pressure relief valves.

• Process Documentation: Identify fermentation as a controlled step within the HACCP plan, with critical limits, monitoring frequencies, corrective actions, and verification activities defined.

• Verification and Validation: Confirm the effectiveness of fermentation parameters through periodic trend analysis (reviewing logged readings for patterns) and validation data (scientific evidence demonstrating that the process achieves the intended control). Maintain validation data and venting design specifications within the scientific support file.

• Training and Corrective Action: Train staff to recognize signs of overactive fermentation and outline immediate corrective steps, including safe venting and hold procedures.

All monitoring and verification records should be retained for at least one year for refrigerated products or two years for shelf-stable items, consistent with federal recordkeeping requirements.

In Practice

Exploding fermentation is not a new phenomenon. Historically, open fermentation systems relied on natural gas diffusion and visual cues to gauge microbial activity. Modern production methods enclose these same processes within engineered systems that require mechanical venting, parameter verification, and documented controls.

At AgriForaging Compliance Services, fermentation is approached as both a biological art and a technical system. Our work supports producers in aligning traditional fermentation practices with measurable, compliant, and verifiable standards under HACCP and GMP frameworks. Proper control transforms fermentation from an unpredictable risk into a stable, validated process that preserves both food safety and craft integrity.

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