How Dangerous is Your Christmas – 1. Food

Scientists Dave Porter and Fran Scott show Dick and Dom some festive science experiments. If you would like to try them yourself, here’s how!

The science behind red cabbage, Brussels sprouts and how Santa gets down the chimney.

Activity 1: How does Santa get down the chimney? (The egg in a bottle experiment)

This experiment requires an adult’s assistance.

We can’t actually get hold of Santa to show us his tricks as he’s rather busy at this time of year – but here’s an experiment which shows you how you can get something big to go down something small.

You will need:

  • a glass bottle
  • a peeled hard-boiled egg
  • half a sheet of A4 paper

The bottle needs to have quite a wide neck, so that the egg sits in it as if in an egg cup.

Roll the paper into a thin strip. Ask an adult to light it and pop it in the bottle. Then place the egg on top. Watch what happens when the flames go out – the egg should get sucked into the bottle.

What’s happening?

The burning of the paper produces smoke, and steam. As the temperature drops again, the steam condenses into water, which takes up less space than the steam, creating a partial vacuum in the bottle. This creates a pressure difference - the air outside the bottle is higher pressure than the air inside the bottle. As a result, the egg gets pushed into the bottle.

To get the egg out again you need to blow into the bottle. Cover the entire mouth of the bottle when you do this. This creates higher pressure in the bottle and the egg should come out...

Activity 2: Red Cabbage pH indicator

This activity uses boiling water so will need adult supervision.

A pH indicator is a way of measuring the acidity or alkalinity of a substance. In this activity, you can make your own indicator for testing the pH of some items you can find in the kitchen.

You will need:

  • 6-7 leaves from a red cabbage
  • Boiling water
  • A heatproof jug
  • 3 small heatproof cups or glasses
  • Vinegar
  • Lemon juice
  • Bicarbonate of soda

Tear the cabbage leaves up into little pieces and put them into a heatproof jug. Pour boiling water over them and leave to stand for 5-10 minutes.

Strain your mixture, keeping the coloured water. Pour a bit of the cabbage water into some small clear or white glasses or cups (remember it’s hot, so you will need to use heatproof cups).

Now use your indicator to test a few common acids and alkalis. In one cup, add a few drops of vinegar. In another some lemon juice. Both lemon juice and vinegar are acids. Watch what happens to the liquid. Both will make the cabbage water change colour. Can you tell which is the stronger acid? In a third cup, try some bicarbonate of soda (an alkali). What colour does your indicator turn?

Activity 3: The Brussels sprouts taste test

Does everyone in your family like sprouts? There is a chemical called PTC (phenylthiocarbamide) which cannot be tasted by people with a particular genetic variation, but for those who can taste it, it’s very very bitter. Brussels sprouts contain a very similar chemical, which means that some of us will find sprouts very bitter to taste. Of course, as Dick and Dom find out, there are lots of factors which determine whether or not you like a food, but if you’re from a family with a great love – or hatred! – of sprouts, maybe there’s a reason why!