Science Buddies: "Ask an Expert"

For my science project, I will be experimenting with yeast. I want to find out what increases and what decreases the growth of yeast. So, I will put 2tsp of yeast and 5 mL of room temperature water into a foam cup ( with measurements marked on it). I will make 5 cups of this. In one cup, I will mix in half teaspoon sugar. In the second cup, I will mix in half teaspoon of salt. In the third cup, I will mix in half teaspoon of baking soda. In the fourth cup, I will mix in half a teaspoon of red chilli powder.( Will chilli powder affect anything?) In the fifth, I will not add anything. Then, i will make another set with chilli powder AND salt, ect. How will I measure the growth ( increase or decrease) ? What else should i do to improve this experiment? PLEASE HELP, ASAP!

Thankyou

Hi,

That's a good project idea, and you have the beginning thought out pretty well. We have some similar projects on our website, one of them I think will help you is this one. Can you have a look at it and let me know if it answers your question. There is an apparatus you can build and it tell syou how (and why) here:

https://www.sciencebuddies.org/science- ... ml#summary
Let me know what other questions you have.

Tonya

Hi Kelsey,

As yeast divide and grow they digest sugar and one of the byproducts of their meal is gas--carbon dioxide. The best way to measure yeast growth is by measuring the volume of CO2 that they produce. This is easy to do in the lab where you have flasks, and tubing and graduated cylinders. Do you have access to a school lab?

What you need to measure the volume of the gas produced is a gadget called a eudiometer: http://en.wikipedia.org/wiki/Eudiometer

Go to the wiki and look at the picture showing the "Scheme of the Eudiometer". It is just a test tube with a rubber stopper that has a hole in it for a glass tube that passes underneath a collector into which the gas flows. The collector is graduated in milliliters so you can measure the amount of gas. You have to fill the collector with water first.

You would put your yeast mixture in the test tube, cap it so that there's no leakage then put the tube into the collector and let the yeast grow for some time. The yeast with nothing added is the control. With sugar you should get a lot of CO2 formed. With salt and baking soda very little. Chili powder may have something the yeast can eat so i don''t know what will happen.

I don't know any other way to measure the growth of your yeast that you would be able to do simply and quickly. Gas production is probably the way to go if you can get the test tubes, stoppers with holes, tubing and graduated collectors.

Let us know if you need any other help.

Good luck!

Sybee

Thankyou for your replies. I do not have access to a lab, though. I also added turmeric as one category and sugar and turmeric. They say that turmeric helps fight fungus, bacteria, ect. Up till now, sugar has risen the most. The turmeric mixed with sugar was the highest but then, some of the bubbles deflated. What does this signify? Why is this occurring? The mixture with only turmeric has risen 1.5 centimeteres.

Hi Kelsey,

Using the height of rise of the bubbles is NOT a very good way to compare the relative activities of yeast in the presence of various substances. Turmeric particles may cause some change in the surface tension or strength of the bubbles so they break quicker. What happened with the chili powder?

Are you taking photos of the yeast solutions at specific times after you add the substances? You should do that so you have a visual record. You could put a small ruler into the solution and photograph that to show the height of the bubbles.

Next time try to plan on doing a proper experiment using apparatus to measure the gas volume accurately. You can do these experiments at home. Either borrow the equipment or purchase it from one of the vendors of scientific supplies. Test tubes and stoppers don't cost much and you can use them again for another experiment.

Let us know how the rest of your experiment turned out with the salt and baking soda.

Sybee

Thank you for your reply. Is there another way that I can expand my project and improve it? Luckily, I have another day, and I am hoping to greatly improve my project and hopefully turn it in the day after tomorrow.
With the salt and the baking soda, nothing happened. It did not rise, surprisingly. But one thing I found out was that red chilli powder does contain enough nutrients to grow yeast. It also contains sugar, around 5 grams to be exact. I proved this by putting in chilli powder with other substances.
Example: SUBSTANCE :
Baking soda : first hour, no change. Second hour, no change.
baking soda & red chilli powder:First hour, rose 0.8cm. Second hour, no change

Vinegar rose 0.7cm, as well during the first hour. The second hour, it didn't rise at all; it looked like spoiled milk. Probably killed the yeast by then with its acidity.

Please give me some next steps for improvement!

You don't have much time, so i would stick with testing different kitchen items. Try comparing white and brown sugar, honey, artificial sweeteners, maple syrup, molasses, cornstarch, non-diet soft drinks, juice, garlic, turmeric, etc. Remember to do three test readings for each substance so you can average them and prove differences statistically. I can show you how to do that if you don't know how.

Also, be extra careful to use exactly the same amount of yeast in the same volume of liquid and the same temperature each time as all of these might affect the gas and bubble formation. That's another reason to do do three tests per sample, in case there is a slight error somewhere that affects the bubble height. When you average a number of readings, your error rate decreases and your data are more precise.

Good luck and do let us know how it turns out.

Sybee