Level 1 · Lesson 3

Types of
contamination

Contamination means something is in the food that should not be there. There are four kinds, and one of them causes most of the harm.

A tray of sandwiches on a buffet. A pack of chicken pasta on a chilled shelf. Both look perfect. Both smell fine. Neither tells you a thing about whether they are safe.

What makes food unsafe is nearly always something you cannot see.

The four types

Every hazard you meet falls into one of four groups

Microbiological

Bacteria and viruses. Salmonella from raw chicken, norovirus from unwashed hands. Invisible, and behind most food poisoning.

Physical

A solid object in the food. Glass from a broken jar, a staple from a delivery box, a piece of bone, a hair, packaging.

Chemical

Cleaning product, sanitiser or lubricant reaching food. Often from chemicals stored above food, or a surface used before it dried.

Allergenic

An allergen where the customer does not expect it. Peanut traces, milk in a dairy-free dish, wheat in a gluten-free line.

Knowing which type you are dealing with tells you how to control it.

The four types

Name the hazard

Choose the group each one belongs to.

MicrobiologicalTemperature, time and hygiene

PhysicalHandling, packaging and equipment checks

ChemicalStorage, and letting surfaces dry

AllergenicSeparation and accurate labelling

Why bacteria matter most

In the right conditions, bacteria double roughly every 20 minutes

1

Start

2

20 min

4

40 min

8

1 hour

Millions

A few hours

A single bacterium is harmless. This is why time out of control is the thing that hurts you, and why bacteria cause most food poisoning.

Why bacteria matter most

Move the clock

1

bacteria, starting from one, in the warm and moist conditions they like best

0 hours 0 minutes out of control

0h2h4h6h8h

Something cooked at nine in the morning and still on the bench at two has had five hours of exactly this.

What bacteria need

Four conditions, and they need all of them

Warmth

Room temperature suits them best

Moisture

Wet foods more than dry ones

Food

Protein and nutrients to feed on

Time

Long enough to multiply

Take away any one of the four and they struggle. Nearly every rule in this course removes one of them. Chilling takes the warmth. Working quickly takes the time.

Your turn

What would you do?

A batch of rice was cooked at 9am and left in a covered tray on the bench. It is now 2pm. It looks completely normal and smells fine.

Tap anywhere to continue

High-risk foods

Some foods give bacteria everything they want

Cooked meat and poultry

Moist, high in protein, and already cooked, so nothing will kill bacteria again before it is eaten.

Dairy

Milk, cream, and soft cheese are wet and nutrient rich, and they are usually eaten without any further cooking.

Cooked rice and pasta

Often cooked in bulk and left standing to cool, which is exactly the mistake. Cooked rice is a classic cause of outbreaks.

They are all moist, full of nutrients, and frequently left sitting at room temperature. Three of the four conditions arrive with the food itself.

The most important point in this lesson

Your senses cannot tell you food is safe

Looks fine

No visible change

Smells fine

No off odour

Tastes fine

And tasting is never the check

Judge food by the rules, not by your senses

The five things to remember

1There are four types of contamination: microbiological, physical, chemical, allergenic

2Bacteria cause most food poisoning

3Bacteria need warmth, moisture, food and time to multiply

4High-risk foods include cooked meat and poultry, dairy, and cooked rice and pasta

5Food can look and smell perfectly fine and still be unsafe

Sample question

One question from the quiz

Which four conditions do bacteria need in order to multiply?