1 Food decays because of the presence of bacteria and moulds - small fungi. Both thrive in damp, warm conditions. Revise the main ways of preserving food: drying; chilling; freezing; and mixing with chemicals (vinegar, sugar or salt) that prevent or slow the growth of micro-organisms. Ask children to keep these in mind as they:
* Name one food that is preserved by each process.
* Find a food at home that is preserved by each process.
* Explain how each process works. Vinegar and lemon juice are very acid. Salt and sugar draw the water out of micro-organisms.
2 Yeast is a living organism - a type of mould - that can be grown in the classroom. Given warmth, moisture and food, it gives off carbon dioxide.
Take plastic bottles - those for Panda pop drinks are best - and half-fill one with water at body temperature and add a teaspoonful of dried yeast and a teaspoonful of sugar. Plug the top with cotton wool - which allows gases in and out, but keeps out micro-organisms - and shake the bottle gently. Leave in a warm place and watch.
Set up a second bottle using cold water. Compare it with the warm one. Put it in a bowl of water from the classroom hot tap and watch what happens. You should see that bubbles of gas (carbon dioxide) are produced as the yeast respires. Warming the water increases the rate of respiration; letting it cool slows it. Water that is too hot kills the yeast, and there is no bubbling.
Fermenting yeast raises bread and other dough mixtures. The yeast goes on producing carbon dioxide gas until alcohol - a product of its anaerobic (oxygen-less) respiration - builds up in the bottle and kills the yeast.
Look at the food eaten in the period of history you are studying. How was it preserved? Why was April called "the cruellest month"? (Preserved food often ran out after the winter but little fresh food was available - and death rates soared.) Taking pages 20-21 as a model, ask pupils to make a time line of important food preservation dates before 1900 using books and the internet as sources. If you're studying explorers, find out what food they took with them. Find out about Captain Cook and lime juice and why English sailors were called "Limeys". Research the discoveries of Louis Pasteur.
In your study of "significant places and environments", research local food and ways it is preserved. Many societies dry food - fruit and vegetables, even meat. Find out about sun-dried tomatoes and pemmican.
Design and technology
Ask children to design packaging for preserved food of all kinds. Explore the ways that foods are preserved and stored by food producers. How is the food made palatable? How does it return to its original state - vegetables and croutons in freeze-dried soups, for example.
Ask the school meals service about food preservation. Visit a shop or supermarket and find out about "best before dates" and how food is prepared and stored. Teach about safe food storage.
This feature supports the following QCA schemes of work:Science key stage 2 Sc2 5fDesign and technology KS2 5cPSHE and Citizenship KS2 3A and 3B