Food preservation – bacterial growth by temperature and time
Design & TechnologyFood & TextilesAges 11–12
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Food & Textiles
A food sample is left at a chosen temperature: bacteria on the food double at a generation time that depends on temperature, fastest in the 5–60 °C danger zone and almost stopped in the refrigerator (0–5 °C) or freezer (−18 °C). Students drag the thermometer to change the temperature, choose a preservation method (left at room temperature, refrigerated, frozen, dried, pickled, canned), then press Run to see the bacteria count, a chart over time, and the moment the food spoils.
Lesson: Preserving and processing food at home: role, preservation methods and food hygiene and safety
What it shows
Most food spoilage is caused by bacteria that multiply by binary fission. The simulation uses a doubling time that depends on temperature: growth is fastest in the danger zone of about 5–60 °C, peaking near 37 °C where the population can double every 20 minutes, becomes very slow in a refrigerator and stops in a freezer. Because the count grows exponentially it is plotted on a log scale, and the food counts as spoiled above 10⁷ bacteria per gram. Drying, pickling and sterilised canning slow bacteria in other ways: removing water, lowering pH, or killing them and sealing the food.
How to use
Pick a Food, choose the Preservation method Left in open air, set the Storage temperature to about 30 °C and press Run. Note how many hours pass before the food spoils. Reset and repeat with Refrigerator, Freezer and the other methods for the same food, comparing the curves. Press Cook at 100 °C partway through to see reheating cut the bacteria count, then keep running to check whether growth resumes. Raise the Playback speed for long storage times.
Parameters you can change
- Food Fresh pork, Fresh fish, Fresh milk, Leafy vegetables, Cooked rice
- Storage temperature -18–45 °C
- Preservation method Left in open air, Refrigerator (0–5 °C), Freezer (−18 °C), Dehydrating, Pickling, Sterilised canning
- Playback speed (simulated hours per second) 0.5–6 h/s
Questions to explore
- How long does cooked rice take to reach 10⁷ bacteria per gram at 30 °C, and how long in the refrigerator?
- Why does refrigeration only delay spoilage, while freezing at −18 °C stops bacterial growth?
- After you press Cook at 100 °C, why does the bacteria count rise again if the food is left out?
