The chef has left a tray of cooked rice on the galley bench to cool while he does the guest lunch service. It is 31 degrees in the galley. Two and a half hours later it goes into the fridge, and tomorrow it becomes a fried rice for the crew. You have just watched a textbook Bacillus cereus incident being built, one hour at a time.
The four groups of micro-organism
| Type | Grows in food? | Why it matters |
|---|---|---|
| Bacteria | Yes, rapidly | The main cause of food poisoning; some form spores or toxins |
| Viruses | No - they need a living host | Carried on food; a tiny dose infects (Norovirus, Hepatitis A) |
| Moulds | Yes | Mostly spoilage; some produce mycotoxins |
| Yeasts | Yes | Mostly spoilage - fermentation, fizzing, off flavours |
Because viruses do not multiply in food, temperature control does not control them. Only hygiene, exclusion of sick handlers, safe water and proper cooking of shellfish do.
What bacteria need to grow
Remember FAT TOM, or simply: food, moisture, warmth and time (and, for some, oxygen).
- Food - protein-rich, high-risk foods above all.
- Moisture - measured as water activity (aw); drying, salting and sugaring lock it away.
- Warmth - the danger zone, widely taught as 5 degrees C to 63 degrees C, with fastest growth near body temperature.
- Time - in ideal conditions bacteria divide roughly every 10-20 minutes by binary fission. One cell becomes millions in a few hours.
- Oxygen - aerobes need it; anaerobes (e.g. Clostridium) grow without it, which is why the middle of a large stew or a rolled joint is dangerous ground.
- pH - most pathogens dislike strongly acidic conditions.
The growth curve has four phases: lag (adjusting, no growth - this is the phase good practice keeps them in), log (exponential growth), stationary (nutrients run out), decline (die-off). Every hour a high-risk food sits in the danger zone spends the lag phase you were relying on.
Spores and toxins - the two facts exams love
- Spores are dormant, armoured survival forms made by Clostridium and Bacillus. They survive normal cooking, including boiling. When the food cools slowly, they germinate into growing bacteria. Reheating does not always save you.
- Toxins are poisons. Some are made in the food before you eat it (intoxication), some in the gut. The toxin of Staphylococcus aureus is heat-stable: you can kill every bacterium in the food and the toxin will still make people ill. Bacillus cereus likewise leaves an emetic toxin in cooled rice that reheating will not destroy.
Hence: infection (live bacteria multiply in you - Salmonella, Campylobacter) versus intoxication (a pre-formed poison - Staph aureus, emetic B. cereus). "Food poisoning" is often used loosely for both.
High-risk foods
Ready-to-eat, moist, protein-rich, needing refrigeration:
- Cooked meat and poultry, and their stocks, gravies and sauces
- Dairy: milk, cream, custard, soft and unpasteurised cheeses
- Eggs and egg products (mayonnaise, mousse, tiramisu)
- Shellfish and other seafood
- Cooked rice and cooked pasta
- Prepared salads, pate, hummus, cut fruit, sprouted seeds
Onboard Notes
Galleys run hot and cramped, cooling is slow, and the fridge is always full - the three conditions bacteria most enjoy. Never cool food on the bench "just while service finishes". And remember the shellfish rule: bivalves filter seawater, so a bay with a marina, an outfall or a hundred anchored yachts is exactly where you do not source or collect oysters and mussels.
Scope note: xplor is not an approved centre or an accredited training provider. This lesson is preparatory study only - no certificate and no regulated qualification is awarded here, and the Level 2 food safety award must be sat and assessed with an approved centre of a regulated awarding organisation.