---
title: "Why Food Goes Bad and How to Stop It"
description: "Food spoils because microbes grow in it, and every preserving method is an attack on one of the things they need: warmth, water, air or time. Cooking, chilling, drying, salting and canning are the sam"
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source: https://lightmysky.com/learn/design-and-technology/why-food-goes-bad-and-how-to-stop-it-mt_Nw5F4g18lY.md
retrieved: 2026-09-12
---

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# Why Food Goes Bad and How to Stop It

Food spoils because microbes grow in it, and every preserving method is an attack on one of the things they need: warmth, water, air or time. Cooking, chilling, drying, salting and canning are the same idea applied differently.

Subject: Design & Technology · Area: Food & Cooking · Ages 12 to 14
Page: https://lightmysky.com/learn/design-and-technology/why-food-goes-bad-and-how-to-stop-it-mt_Nw5F4g18lY

## Ready when they can

- Name what microbes need to grow and match each preserving method to the thing it removes
- Explain why the fridge slows spoiling but does not stop it
- Say what cross-contamination is and give one habit that prevents it
- Explain the difference between a use-by date and a best-before date, and which one matters for safety

## Lesson: Why food spoils and how you stop it

Food spoils because tiny microbes grow in it. They need warmth, water, air, and time to multiply. Every preserving method attacks at least one of those needs.

**Example.** Chilling in the fridge slows microbes down, but it does not stop them, so old leftovers still turn. Drying takes their water away, salting draws water out, and canning seals air out with heat. That is why dried fruit, salty ham, and sealed cans all keep longer.

Microbes also hitch rides, which is called cross-contamination. Juices from raw chicken can carry them onto salad, hands, and boards. Wash fruit like melon before cutting, and keep raw and ready foods apart with clean hands and tools.

**Tip.** Read packet dates with care. A use-by date is about safety, so do not eat the food after it passes. A best-before date is about quality, so the taste may fade but the food can still be safe.

**Recap.** Starve microbes of warmth, water, air, or time, block their rides between foods, and respect the use-by date.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Reading a Food Label](https://lightmysky.com/learn/design-and-technology/reading-a-food-label-mt_1oQ_cPb_-T)
- [Gut Bacteria & Digestion](https://lightmysky.com/learn/science/gut-bacteria-and-digestion-mt_fCvmdI6xGO)

## Opens up

- [Cooking Methods That Carry Across Recipes](https://lightmysky.com/learn/design-and-technology/cooking-methods-that-carry-across-recipes-mt_-fGuaw1mON)
- [Planning Meals for a Whole Week](https://lightmysky.com/learn/design-and-technology/planning-meals-for-a-whole-week-mt_T_GY879Oa7)