Bacteria and Food: How Germs Grow and Spread (FATTOM)

Bacterial growth in food depends on factors summarised by FATTOM: Food, Acidity, Time, Temperature, Oxygen and Moisture. Food handlers reduce growth by controlling time and temperature, keeping food covered and dry where appropriate, preventing contamination, following validated recipes, and applying HACCP-based procedures under Regulation (EC) No 852/2004.

How Do Bacteria Multiply in Food?

Key takeaway: Bacteria multiply when food and environmental conditions support growth, but contamination and multiplication are two different stages of the risk.

Bacteria are microscopic organisms that reproduce by dividing. Some bacteria are useful or harmless, while others can spoil food or cause foodborne illness. A food may first become contaminated through raw ingredients, hands, equipment, cleaning materials, splashes or contact with another food. Bacterial numbers can then increase when the contaminated food is held under favourable conditions. Codex identifies food handlers, surfaces, cleaning equipment, splashing and airborne particles as possible routes of microbiological contamination.

This distinction matters for food handlers:

• Contamination introduces microorganisms into or onto food.

• Growth increases the number of microorganisms already present.

• Survival means microorganisms remain alive despite a control such as chilling or incomplete cooking.

• Toxin production occurs when certain bacteria produce harmful substances under suitable conditions.

A food handler may therefore create risk in two ways: by transferring bacteria to food or by allowing contaminated food to remain in conditions that support growth.

For example, a clean utensil used on ready-to-eat food presents less risk than one that has just touched raw poultry. However, even food handled with clean equipment can become unsafe when it is cooled too slowly, left outside temperature control or stored beyond its safe life.

Regulation (EC) No 852/2004 requires food to be protected against contamination throughout production, processing and distribution. It also requires foods capable of supporting pathogenic microorganisms or toxin formation to be kept at temperatures that do not create a health risk.

What Does FATTOM Stand For?

Key takeaway: FATTOM is a training mnemonic for the principal food and environmental factors that influence bacterial growth.

FATTOM stands for Food, Acidity, Time, Temperature, Oxygen and Moisture. It gives food handlers a practical way to remember why some foods support rapid bacterial growth while others are less favourable.

FATTOM is not a legal checklist or a guarantee that food is safe. Different bacterial species respond differently to each factor, and the factors interact. The European Food Safety Authority has noted, for example, that bacterial growth can depend on temperature, water activity and pH rather than on one condition alone. 

Food

“Food” in FATTOM means the nutrients available to bacteria, not simply the presence of something edible. Prepared foods containing protein, starch or other nutrients may support growth when the remaining FATTOM conditions are also favourable.

Food handlers cannot remove nutrients from most dishes, so they normally control bacterial growth through other factors—particularly time, temperature, moisture, acidity and contamination prevention.

Acidity

Many pathogens grow less effectively as acidity increases, but there is no universal pH value that makes every food safe. The required control depends on the organism, food formulation, processing method, packaging and intended shelf life.

Acidification, fermentation and preservation are therefore technical controls. A food handler should follow the approved recipe precisely rather than adding more water, reducing vinegar, changing ingredient quantities or shortening a fermentation stage.

Time and Temperature

Time and temperature usually provide the most practical controls in day-to-day food handling. Codex states that inadequate time and temperature control during cooking, cooling, processing and storage is among the most common failures of operational control. It recommends considering the food’s pH, water activity, microorganisms, shelf life, packaging, processing and intended use. 

This is why food handlers must:

1. Receive chilled and frozen food promptly.

2. Follow approved storage limits.

3. Minimise unnecessary time outside temperature control.

4. Cook, cool and reheat food according to the food-safety procedure.

5. Record temperatures where the business requires records.

6. Report equipment failures or temperature deviations immediately.

Oxygen

The “O” in FATTOM needs careful explanation. Not all harmful bacteria need oxygen. Some grow in its presence, some grow without it, and others can adapt to either environment.

Removing air can slow particular spoilage organisms, but it may create conditions suitable for other hazards. Vacuum packing and modified-atmosphere packaging therefore require validated controls covering temperature, shelf life, product formulation and packaging integrity.

Moisture

Bacteria need water that is available for biological activity. This is different from the total amount of water in a product. Salt, sugar, drying and other formulation methods can reduce water availability, but they must be applied through an approved process.

A dry ingredient may also become more hazardous if it absorbs water from condensation, wet utensils or poor storage. Food handlers should close containers, use dry scoops and report damp packaging or moisture damage.

How Can Food Handlers Control Bacterial Growth?

Key takeaway: Food handlers control bacterial growth by following the approved process rather than trying to calculate microbiological risk themselves.

Food handlers are not expected to design product formulations or establish scientific safety limits. Their responsibility is to apply the controls established by the food business and its hazard analysis and critical control point procedures.

Regulation (EC) No 852/2004 requires applicable food businesses to implement and maintain permanent procedures based on HACCP principles. These include identifying hazards, setting critical limits where appropriate, monitoring controls, taking corrective action, verifying effectiveness and maintaining proportionate records. 

Practical FATTOM Control Checklist

• Keep raw food separate from ready-to-eat food.

• Wash hands at the required times.

• Use clean and, where necessary, disinfected equipment.

• Follow approved cooking, cooling, chilling, freezing and reheating procedures.

• Minimise the time perishable food spends outside controlled storage.

• Check and record temperatures according to the business procedure.

• Keep dry ingredients protected from water, condensation and wet utensils.

• Follow recipes and formulation instructions exactly.

• Observe use-by dates, prepared-on dates and internal shelf-life labels.

• Report refrigerator failures, damaged packaging and unsafe temperature readings.

• Discard or isolate affected food according to the corrective-action procedure.

• Never rely on smell, appearance or taste alone to decide whether food is microbiologically safe.

Codex also recommends that temperature systems affecting food safety be validated, monitored where appropriate and supported by devices checked for accuracy and calibrated as necessary. 

Practical Scenario

A container of cooked sauce is left on a preparation counter during a long service period.

The sauce supplies nutrients and moisture. Its acidity may permit growth, and its temperature may become suitable for certain microorganisms. The longer it remains under those conditions, the greater the opportunity for bacterial multiplication.

The handler’s correct action is not to estimate how many bacteria may be present. The handler should follow the business’s time-and-temperature rule, return the food to controlled storage where permitted, or isolate and report it when the approved limit has been exceeded.

Country variations: Regulation (EC) No 852/2004 establishes the EU-wide hygiene framework, but national authorities and sector guides may specify temperature targets, monitoring practices or other operational expectations. Food handlers should follow the procedures approved for their workplace and the guidance of the competent authority in the relevant Member State. 

What Are Bacterial Spores and Toxins?

Key takeaway: Cooking may destroy many actively growing bacterial cells, but some spores or previously formed toxins can require additional controls.

Some bacteria can form resistant structures called spores. Spores are dormant survival forms rather than actively multiplying cells. When conditions later become favourable, they may germinate and produce growing bacterial cells.

Certain bacteria can also produce toxins in food. A toxin is a harmful substance, not a living bacterium. Depending on the organism and toxin, ordinary reheating may not remove the hazard reliably.

This is why food safety cannot depend on reheating alone. The complete process matters:

• Use suitable ingredients.

• Prevent contamination.

• Cook according to the validated procedure.

• Cool food promptly.

• Store it under the required conditions.

• Observe the established shelf life.

• Reheat only as permitted by the business procedure.

Codex specifically recognises that product composition, pH and water activity can be important in preventing microbial growth and toxin production. It also identifies cooking, chilling, freezing, drying and packaging as process steps that may contribute to safe food production. 

EFSA’s work on the Bacillus cereus group illustrates why this matters: members of the group can cause foodborne illness, and risk management must consider bacterial concentrations and toxin-producing potential rather than relying solely on the appearance of the food.

What Does EU Food Hygiene Law Require?

Key takeaway: EU law requires food businesses to control contamination and microbial growth, while food handlers must be trained and follow the controls relevant to their work.

Regulation (EC) No 852/2004 does not use the term FATTOM. The mnemonic is a training tool that helps explain the science behind several legal and operational requirements.

Under the Regulation, food business operators must:

• Protect food from contamination.

• Maintain appropriate temperature-controlled handling and storage where necessary.

• Avoid keeping foods at temperatures that could create a health risk.

• Apply HACCP-based procedures where Article 5 applies.

• Ensure food handlers are supervised, instructed and/or trained in food hygiene to a level appropriate to their work. 

Codex CXC 1-1969 is an internationally recognised code of practice rather than EU legislation. It supports professional good practice by explaining general hygiene programmes, time-and-temperature control, contamination prevention and HACCP principles. 

Understanding how bacteria grow in food helps handlers understand why routine rules matter. Handwashing, separation, refrigeration, prompt cooling, correct cooking and accurate labelling are not isolated tasks: together, they remove opportunities for bacteria to contaminate food, survive or multiply.

Build Safer Food-Handling Habits

Key takeaway: Effective food hygiene training turns microbiological principles such as FATTOM into consistent daily actions.

Food handlers do not need to become microbiologists, but they must recognise the conditions that allow bacteria to grow and act before food becomes unsafe. Adjacent task guidance includes  What Is a Food Handler? Roles & Responsibilities

The food hygiene for food handlers guide explains the wider daily rules for personal hygiene, safe handling and contamination prevention.

The Basic Food Hygiene for Food Handlers Course  provides structured training on the practical habits food handlers need to apply during preparation, storage, service and cleaning.

This article provides general educational guidance and is not legal advice. National legislation, competent-authority guidance and workplace procedures may add requirements.

Sources and Methodology

Key takeaway: This article is based on EU legislation, Codex guidance, EFSA material and practical food-hygiene principles.

The article was prepared using the target search intent, current authoritative sources and recognised food-hygiene practice. Technical claims were checked against:

• Regulation (EC) No 852/2004 on the hygiene of foodstuffs, including Article 5 and Annex II. 

• Codex Alimentarius General Principles of Food Hygiene, CXC 1-1969. 

• European Commission food-hygiene legislation and guidance resources. 

• European Food Safety Authority material concerning microbial growth factors and bacterial hazards.