Science is important for exploring, discovering and solving problems in our world.

Children's access to and engagement with world-class science centres, experts and resources can be inhibited for those living in small towns or geographically isolated regions or by a reluctance for many teachers’ to conduct science experiments in the classroom.

Due to a lack of self-efficacy in subject knowledge, the necessary resources or preparations and particularly, the potential safety implications, hands-on science is often absent in schools.

That is where the Shell Questacon Science Circus comes to the rescue.

For almost thirty years, the Science Circus has visited schools and communities across the country, bringing the thrills and excitement of science to kids of all ages.

From Longreach to Launceston, Broome to Byron Bay, the moment Questacon’s flagship outreach program arrives in the semi-trailer; children and educators are in for ‘edutainment’ – entertaining education.

The Science Circus is not just your run of the mill science demonstration. Alongside in-school performances for primary and secondary schools, the program includes interactive science exhibitions for the whole community and hands-on professional development workshops for teachers. With digital incursions increasing in popularity, Questacon’s Science Circus also broadcasts interactive activities and live discussions with video-conferencing technologies.

In partnership with Shell and The Australian National University, the Science Circus is staffed by young science graduates who are undertaking further studies in science communication. These passionate presenters have a unique opportunity to further their education ‘on the road’, while sharing their love of science with children who may be thousands of kilometres away from Questacon – The National Science and Technology Centre in Canberra. Showing that science is relevant to everyone, these role models are hard-pressed to contain their enthusiasm.

Questacons’ Stop the Rot experiment is ideal to try in your classroom or at your school during National Science Week 2014  'Food for our future: Science feeding the world' from August 16 to August 24. This experiment engages children in food sustainability practices and is just one example of simple, low-cost science experiments that are available for teachers to help extend the learning and discovery experiences for their children.

Stop the rot

Inquiry question: How did people keep food from going off before they had fridges? Discover how a little salt can keep your food edible for months (if you don't mind salty food).

You will need:

  • 1 apple
  • 1 pop stick (from a craft shop or ice block)
  • 1 (kids safe) knife
  • 1/2 cup salt
  • 1/2 cup bicarbonate of soda
  • 2 plastic cups
  • 1 mixing bowl
  • paper
  • pencil

Step by Step:

  • Cut the apple into quarters.
  • Carve a face into one of the apple quarters using a pop stick. You can make any face you like.
  • Weigh the apple face and record its weight
  • Place the apple face into a dry plastic cup.
  • Add 1/2 a cup of salt and 1/2 a cup of bicarbonate of soda into the mixing bowl and mix well to create a salt mixture.
  • Pour some of the salt mixture over the apple face so that it is completely covered. Tap the sides of the cup to make sure that the salt mixture fills all the little air pockets. Fill the cup with the rest of the salt mixture to completely cover the apple.
  • Store in a warm, dry place, away from direct sunlight.
  • Carve a face into another of the apple quarters and record its weight. Place it in the other plastic cup but do not add salt mixture. Store alongside the other apple.
  • Wash your hands
  • Discard the remaining apple quarters (or have a friend repeat steps 1 to 8 with the remaining apple quarters).
  • After a week, remove the apple quarters from their containers. Gently brush off any excess salt mixture (do not wash with water).
  • Weigh each apple quarter. Record the new weights.
  • Compare the appearance of the salted apple with the unsalted apple. Compare the weights of the salted apple with the unsalted apple.
  • Optional: Return the apple quarters to their original plastic cups.  Ensure the salted apple quarter is completely covered by the salt mixture.  Store the cups in their original locations for another week.  Repeat steps 11 to 13.  Discard the cups, salt mixture and apple quarters. Wash your hands.

What is happening?

When food is left untreated, bacteria and mould begin to grow on it over time. As the bacteria and mould feed on the food, they produce toxic chemicals that can make the food unsuitable to eat. This process is known as 'rotting'. In this experiment the unsalted apple rots but doesn't lose weight. The salted apple doesn’t rot but does lose weight.

Mould spreads by sending tiny spores into the air which can travel very large distances. If the mould spores settle on a surface they will only grow into mould if the conditions are right. Mould and bacteria require moist, nutrient-rich, low salt environments. Thus the unsalted apple is a very suitable environment for bacteria and mould to feed and grow.  The bacteria and mould feed on the unsalted apple, causing it to rot. That’s why the unsalted apple appears black and squishy in some parts and perhaps smells slightly.

The salted apple, on the other hand, doesn’t appear damaged by rotting and has less mould growing on it. This apple’s environment doesn’t have enough water and is too salty for the bacteria and mould to feed and grow. The water in the salted apple is absorbed by the salt mixture. Due to the loss of water (as well as reactions between the natural chemicals in the apple and the oxygen in the air) the salted apple appears brown and shrivelled.

As most of the water has been removed from the salted apple, it should weigh less than it did a week earlier. The apple left unsalted should weigh almost the same as it did initially, since no water will have been removed.

Salt and bicarbonate of soda are both hygroscopic. This means that they can absorb water from their surroundings, either by touch or through the air. When food is placed in a salt mixture, the salt draws water out of the food, causing it to dry out. Similarly, hygroscopic salts will also draw moisture out of the cells of bacteria, killing them before they can try to grow and spread.  This further helps to preserve and prolong the life of the food.


Find out how much water you can draw from the apples. Put them back in the salt mix and re-weigh them every week. How long does it take to drain all the water out? Calculate the weight of water that has been lost from each apple to find out how much has been absorbed by the salt. Or, try using different types of fruit or food. Which foods preserve well? Which foods continue to rot over time? How watery or salty are each of these foods?

More Questacon science activities for teachers are available at

Click here to view the Australian Science Teacher Associations National Science Week 2014 Food for our Future: Science feeding the world teacher resource book of ideas for lessons pre-school to Year 10