Why does food decay?

Have you ever noticed that if you leave an apple (or any fruit ) for too long it starts to go bad or decay.

This is because micro-organisms such as bacteria, yeasts and fungi feed on the fruit and break it down. Have you also noticed that keeping fruit and vegetables in a fridge makes them last longer? This is because the cold slows down the growth and reproduction of microorganisms  stopping the decay.

Today we are looking at other ways to try to preserve apples.

What you need:

• One apple
• 4 containers
• lemon juice
• vinegar
• salt water ( 1 tablespoon salt dissolved in hot water )

Instructions

• Cut the apple into 4 even pieces.
• Place a segment of apple into each container.
• Cover each apple with the same amount of either lemon juice, vinegar or salt water. Leave one just exposed to the air     ( this is the control ).
• Leave untouched for about a week in a cool place and observe the differences.

Results

Control Apple – you can see this has started to shrivel up, but there is not much evidence of mould.

Salt and vinegar ( vinegar is at the front )

Lemon Juice

The Science Bit

There are many mechanisms of preserving food, all slow or stop the activity of the micro-organisms which make the fruit decay.

As well as refrigeration, you can freeze, can or pickle foods to preserve them.

You can see from the photo’s that in our investigation the apple segment in the salt is the best preserved. This is because salt draws the moisture out of the food so the micro-organisms do not thrive and cannot reproduce as fast as they can in the other conditions.

The vinegar did prevent mould growing, this is because vinegar has anti-microbial properties. This means the vinegar inhibits or kills the microorganisms.

You can see that the lemon juice shows evidence of mould. This could be because the micro-organisms have flourished in the sugary environment.

Extension

Can you think of other things to try? What about bicarbonate of soda? Or trying different fruits?