Outcome. FI: Henkilö tietää miten mikrobeja voidaan hyödyntää elintarvikkeiden valmistuksessa. EN: The person knows how microbes can be used in food production.

Why it matters

Yoghurt, cheese, bread and beer exist because microbes were put to work. "Microbe" does not always mean "danger", but a useful process still needs hygiene and control.

What to know

Beneficial microbes are used in making some dairy products and other foods. Lactic acid bacteria make yoghurt and other sour-milk products. Yeasts are used in bread dough and in beer and wine. Moulds are used on purpose in blue-veined cheeses. Rye bread and buttermilk (piimä) are traditional fermented products.

Fermentation (fermentointi) is a method in which food is soured through the action of microbes. It lowers the pH of the food. The microbes may occur naturally in the food or be added to the process. A long enough fermentation can destroy the natural lectin toxin in some beans.

The greatest food safety risk in fermentation is that the pH does not fall enough, so harmful microbes can grow. Listeria monocytogenes cannot grow below pH 4.4, so a successful fermentation should reach a lower pH. A small operator can check the start of fermentation with pH paper or a pH strip, in addition to judging by sight, smell and taste. An operator that ferments food must describe the process in its own-check and consider it in the hazard assessment.

Mould that grows on food by accident is not a useful use of microbes, and its toxins are not destroyed by heating.

Scenario

A bakery makes rye sourdough. One week the starter looks flat and the pH strip shows a value that is too high. The baker throws it away, because a poorly soured batch lets harmful microbes grow.

Remember

Microbe group	Used for
Lactic acid bacteria	yoghurt, other sour-milk products
Yeasts	bread dough, beer, wine
Moulds	blue-veined cheeses
Fermentation safety	pH below 4.4 stops Listeria

Myth vs reality

• Myth: Microbes are never used in making food. Reality: Many foods are made with useful microbes.
• Myth: Fermented food is automatically safe. Reality: If the pH does not fall enough, harmful microbes can grow.
• Myth: Scraping the mould off jam makes it safe. Reality: Mould toxins are not destroyed by heating.

In the test

"Some" products use useful microbes is true. "Never" or "all microbes are harmful" is false.

Outcome. FI: Henkilö tietää miten mikrobeihin voidaan vaikuttaa esimerkiksi lämpötilan, happamuuden, kosteuden, hapen ja elintarvikkeen koostumuksen avulla. EN: The person knows how microbes can be influenced by, for example, temperature, acidity, moisture, oxygen and the composition of the food.

Why it matters

This is the science behind most food safety rules. When you know what microbes need, you can predict which foods are risky and why the rules are set as they are.

What to know

Temperature. Spoilage bacteria multiply rapidly between +6 and +60 °C. This range is called the danger zone (vaaravyöhyke), and food should spend as little time in it as possible. Low temperature slows or stops growth but does not kill microbes. Listeria and Yersinia can multiply at refrigerator temperatures. Freezing does not kill viruses, so frozen berries can carry norovirus and hepatitis A, and ice cubes can carry microbes. Heating food throughout to over +70 °C destroys most food poisoning bacteria but not necessarily their spores. Norovirus is destroyed at +90 °C for two minutes, hepatitis A at +90 °C for at least five minutes.

Spores. Bacillus cereus and Clostridium perfringens form spores that survive cooking and multiply when food cools slowly. Cooked rice and other moist cooked foods are good growth media if not held hot or cold. Warm food cools faster in a small portion without lid or film. Plastic film does not make warm food safe at room temperature and may slow cooling. Cooling beside an open window is not controlled and exposes food to dust and insects. Overfilling a cold cabinet stops air circulation, so food may not stay cold enough.

Moisture. Microbes need water. Salt and sugar bind free water, so growth is limited in salty, sugary or dried foods. Preservatives slow or stop growth but do not destroy microbes, and preserved food can still carry food poisoning bacteria. Listeria can multiply at high salt levels, so the salt in cold-smoked or gravad fish does not stop it.

Acidity. Adding acidity (lowering pH) inhibits bacteria. Clostridium botulinum cannot grow below pH 4.5. Mould grows well in acidic foods such as jam and juice.

Oxygen. Vacuum packing does not kill microbes. Listeria monocytogenes and C. botulinum can grow in vacuum or gas-packed food, so these products need an unbroken cold chain.

Composition. Slicing, cutting and mincing make food more perishable, and microbes multiply quickly in minced meat. Thawed food can spoil faster than never-frozen food, because ice crystals damage the structure. Perishable food must not freeze during transport. Raw milk kept cold can still contain disease-causing bacteria; pasteurisation (+72 °C for 15 seconds) kills most microbes but not spores, and UHT is stronger. A microwave can leave cold spots where microbes survive.

Scenario

On Friday a canteen leaves a large pot of cooked rice covered in plastic film on the counter overnight. The film does not protect it and may slow cooling. By morning the rice has spent hours in the danger zone and B. cereus has multiplied.

Numbers to remember

Item	Value
Danger zone	+6…+60 °C
Heating that destroys most bacteria	throughout over +70 °C
Norovirus	+90 °C, 2 minutes
Hepatitis A	+90 °C, at least 5 minutes
C. botulinum stopped by	pH below 4.5
Listeria stopped by	pH below 4.4
Pasteurisation of milk	+72 °C, 15 seconds

Myth vs reality

• Myth: Film over warm food keeps it safe at room temperature. Reality: It does not, and it may slow cooling.
• Myth: Refrigeration and freezing kill microbes. Reality: They slow or stop growth only.
• Myth: Food with preservatives cannot cause food poisoning. Reality: Preservatives do not destroy microbes.
• Myth: Thawed food keeps better than fresh food. Reality: It can spoil faster.

In the test

Cooling, film, open windows and cabinet fill limits are favourite topics. The answer is nearly always: cool small portions quickly, uncovered, in equipment made for it.