An Alternative to the Balloon Method for Measuring Yeast
The apparatus shown in the picture permits
more accurate measurement of yeast respiration than the balloon approach. The
carbon dioxide respired by the yeast is trapped in an upside down graduated
cylinder. The milliliters marked on the graduated cylinder let you read
directly the amount of carbon dioxide trapped.
You will need:
- graduated cylinder (100 ml shown).
- beaker or bowl.
- rubber or plastic tubing.
- one hole rubber stopper. A number 3 stopper fits most 1 liter plastic
- short glass or plastic tube. A medicien dropper or piece of a 1 ml
plastic pipet might work. The tube should not touch the liquid culture in the
flask or bottle.
- Erlenmeyer flask or soda bottle (500 ml flask shown).
Directions for assembly:
- Buy one-hole rubber stoppers that fit your bottles or flasks. Your
teacher may be able to help or hobby stores that sell chemistry sets often have
the supplies you will need.
- Insert a short piece of glass or plastic tubing in the hole in the
stopper. It will be easier to insert the tube if you put salad oil on the
outside of the tube. BE CAREFUL. If you break the glass tube you may cut
- Measure and cut a piece of rubber tubing long enough to reach from the
flask to the lower part of the graduated cylinder.
- Slide one end of the rubber tubing over the tube in the rubber stopper.
- Fill the beaker or bowl with water.
- Fill the graduated cylinder all the way to the top with water.
- Cover the top of the graduated cylinder with your hand and quickly turn
it over and put it in the beaker filled with water.
- Remove your hand. There should not be any air in the graduated cylinder.
If there is a small amount of air, record the amount (ml). You will need to
subtract this amount from the total in the cylinder when you take respiration
- Fill the flask or bottle with your liquid yeast culture.
- Insert stopper in the flask or bottle.
- Insert the end of the rubber tube in the graduated cylinder. Do not lift
the end of the graduated cylinder out of the bowl or it will fill with air.
Last update: 13 Apr 00. © 2000. Robert Fogel, Ivins, UT 8473. Edited by