This project idea comes
to you from Science AL!VE in
Burnaby, British Columbia.
- To introduce the science
of microbiology by demonstrating how a carbonated drink such as ginger beer
can be made using the single-celled organism, yeast.
- What makes pop fizzy? It's the dissolved carbon dioxide in the drinks.
One way of carbonating drinks is to use a micro-organism called yeast.
Yeast are tiny single-celled, living plants. When placed in a warm, moist
place and given sugar as a food source, the yeast become active and
multiply. Meanwhile, they produce carbon dioxide gas as a metabolic waste
product. Like in any living thing, the process of life for yeast involves metabolic
processes that, by definition, produce waste. Just like in humans, the
metabolic waste of yeast is carbon dioxide gas. This gas can make drinks
fizzy or can make bread rise.
If a drink that's being carbonated is placed in a sealed container, the
space between the liquid and the cap fills up with carbon dioxide. As the
concentration of carbon dioxide increases, the gas starts to get pushed into
solution and the bubbles stay in the water. This makes the drink carbonated.
If the cap was loose, the gas would escape and you would get "flat" pop. As
long as the yeast have enough sugar to eat, they keep making carbon dioxide.
When the yeast run out of sugar, they start another metabolic process called
fermentation. This process produces alcohol as a waste product. This is why
yeast are used to produce the alcohol found in beer. We refrigerate our
ginger beer so that the yeast don't multiply so much that they run out of
food, and thus produce alcohol instead of carbon dioxide.
- pot filled with 2 L of water
- 1.5 tablespoon of powdered ginger or 0.5 lbs fresh ginger root
- 1/4 lime
- 1 1/4 cups of sugar
- 1.5 tablespoons cream of tartar
- 0.5 tablespoons baker's yeast
- cheese cloth
- funnel and mixing spoon
- 2 L jug with cap or cork
- Boil the
water and add the ginger, juice squeezed from the lime, sugar, and cream of
- Let the mixture cool until it is lukewarm.
baker's yeast and mix well.
- Cover pot and let stand for 6 hours.
- To bottle the ginger beer:
- strain the liquid through the cheesecloth or coffee filter by setting it
on top of the funnel and slowly pouring the liquid into the bottle. (it's OK
if some chunks slip through, they will settle to the bottom).
- be sure to leave an air space at the top of the bottle to collect the
gas so it won't explode.
- Cap the jug tightly and put it into the refrigerator (this is to slow
the activity of the yeast down; if you didn't you might produce alcohol
which would give the ginger beer an unpleasant taste).
- Wait two days. When you take the ginger beer out, look for the
- Slowly unscrew the top of the bottle and listen for the POP sound as the
- You can flavour your ginger beer in many different ways by adding fresh,
chopped mint leaves when you put the ginger in or using honey to replace the
- Yeast is not just used for carbonation. It is also used in a variety of
foods. Long ago, humans figured out a way to turn grains into bread. The
dough used to bake bread is made from ground up grains. When added to
a mass of moist dough, the yeast breaks down the sugars in the dough by
metabolizing it. The dough contains long chains of sugars called starches.
The waste products from breaking down the sugars, as you have already
learned in this experiment, are carbon dioxide and grain alcohol. The
alcohol has a very low boiling point, and usually evaporates. The carbon
dioxide gas puffs up the wad of dough, and that makes the loaf of bread that
tastes so great with a little melted butter.
Yeasts are a type of fungus. They are unicellular organisms, meaning
that the whole organism is made up of only one cell. These organisms are
not at all complex, and they have no systems. Multicellular organisms, on
the other hand, are much more complex. Often they have groups of cells that
work together to perform a specific task. For example, your organs are just
large groups of cells that form tissues, and those tissues together form an
organ. Of course, when scientists are studying things like metabolism, it
is much easier to study it in an organism as simple as a unicellular
organism. Yeasts are very often used for studies in the lab because of
The world is full of unicellular organisms. A few examples are amoeba,
paramecia, bacteria, etc.
Computer Science |
Understanding Science and Technology
Produced by Galactics.
Last updated on 14 August 1998.