Teacher instructions

Work through this resource material in the following sequence:

20 minutes

Tune in: What will change?

20 minutes

Find out: Experiment time!

20 minutes

Reflection: What did we learn?

Tune in: What will change?

Step 1. Discuss:

what makes food rot? Students might be able to say that over time food goes rotten. Students might also have some understanding of bacteria having some interaction with food to cause the decomposition.
is there anything that can prevent or slow down rot? Press students to offer a scientific explanation for their answers. If students say food takes longer to go rotten when placed in the fridge or freezer, ask them why this might be the case.
how do people in from history keep their food fresh without refrigerators? How did they transport food on long journeys via the sea, such as the First Fleet (optional)? Students might have some understanding of the processes of preserving fruits, vegetables, and meat. Ask them to explain, if they can, why these methods were effective. What did they change about the food or the conditions of the food?

Step 2.

Explain the experiment to your students. Explain that you are going to test your theories on what makes it rain.

Step 3.

Students write their predictions in the first section of the Student Worksheet.

Find out: Experiment time!

Step 1.

Using the permanent marker label each jar with the following: 'salt',' sugar', 'hand soap', 'vinegar', 'water', and 'control'.

Step 2.

Place a piece of apple inside each jar. Completely cover each piece of apple with the substance you wrote on the label (for example, in the sugar jar cover the apple with sugar). Don’t add anything to the ‘control’ jar.

Step 3.

Set all the jars in a cool, dry place and leave for a week.

Step 4.

After one week, take all the pieces of apple out of the jars and place them carefully on the paper plates. Be careful not to try and clean them or knock any of the mold off the slices. Compare the ‘rot’. Which ones had the most rot?

Step 5.

Rank the preservatives used from 'most' to 'least' rot allowed.

Step 6.

Discuss:

For the slices of apple that were least rotten, did the preservatives have anything in common?
For the slices of apple that were most rotten, did the preservatives have anything in common?
Were there any 'preservatives' that actually made the apple rot quicker than the control apple, which had nothing applied to it. Why might this have happened?

Reflection: What did we learn?

When something is rotting, it means that it is undergoing a process of decay or decomposition due to the activity of microorganisms like bacteria, fungi, and other microbes.

During the process of rotting, these microorganisms break down the organic matter of the object, like food or plant material, into simpler compounds such as water, carbon dioxide, and various organic acids.

Salt has been used for centuries to preserve food, especially on long sea journeys.

Salt:

draws moisture out of food, an environment that is inhospitable to bacterial growth. Bacteria need moisture to survive and multiply, so by reducing the amount of moisture available, the salt makes it difficult for bacteria to grow and reproduce.
has an antimicrobial effect that helps to kill or slow the growth of bacteria. This is because salt disrupts the cell membranes of bacteria, causing them to lose water and die.

Like salt, sugar reduces the amount of moisture available in food, which can make it more difficult for bacteria to grow. However, sugar does not have the same antimicrobial properties as salt, so it does not directly kill or slow the growth of bacteria.

In addition, sugar can provide a food source for some bacteria and fungi, which can actually promote spoilage rather than prevent it.

Overall, salt and other preservatives prevent food from rotting by creating an environment that is hostile to bacterial growth and by directly killing or slowing the growth of bacteria. That's why salt has been such an important tool for so long, as it helped meet a need and solve the problem of food going rotten. Salt was so valuable to people in ancient times it was known as 'white gold'.

Why Does Food Rot?

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