Christine, Wondering

Random Musings of a Human Becoming

Tuesday, April 24, 2007

Science Experiment

On Monday, in our science curriculum workshop, we did a little mini-experiment. We were given three small jars: one containing a bit of a yeast and tepid water mixture, one containing a bit of a mixture of yeast, tepid water and one teaspoon of sugar, and one containing a bit of a mixture of yeast, tepid water and two teaspoons of sugar. We put balloons over the tops of the jars and watched as they filled with the gas produced by the respiration of the yeast, noting which jar produced the most gas (it was the third one, for the record).

While we were discussing the different variables that one could use in a yeast experiment, one that was mentioned was "the type of sugar". I do a lot of baking so I have a few different sugars around the place, and once I started thinking about it, I counted up no less than 7 different types of glucose-based foods in my stock cupboard.

So, feeling inspired, I stopped off at Target on the way home and bought myself a set of 8 little plastic jars (meant for cosmetics, but perfect for my purposes) and some balloons, and set about doing a yeast experiment for myself.

My ingredients all set out and ready to go

Using a funnel to avoid spillage, I added ¼ teaspoon of yeast to each jar. Then, again using a funnel for the dry sugars, I added ½ teaspoon of the following: 

Jar 1: No Sugar (control)
Jar 2: Glucose Syrup
Jar 3: Golden Syrup
Jar 4: Honey
Jar 5: Brown Sugar
Jar 6: White Sugar
Jar 7: Caster Sugar
Jar 8: Icing Sugar Mixture (contains cornflour as well as sugar - normally I have the pure stuff!)

Then, with the funnel, I added two tablespoons of tepid water (tepid is just warmer than room temperature) to each jar, and then stirred each one briskly and placed a balloon over the top of the jar, ensuring that there was no air in the balloon when it went on.

The jars (left to right = 1-8, they are labelled in red pen if you look closely) just after the balloons went on. No reactions visible yet. Yes, I did the balloon colours that way on purpose!)

As the gas in the balloon increases, the balloon puffs up, and there reaches a point where the balloon will suddenly pop upright due to the pressure of the gas. 24 minutes after I put the balloons on, the first one popped up: 6 - White Sugar.

White sugar balloon puffed up with carbon dioxide

Over the next hour, the balloons continued to pop up, in this order:

1st: 6 - White Sugar (7:07pm)
2nd: 8 - Icing Sugar Mixture (7:10pm)
3rd: 4 - Honey (7:11pm)
4th: 3 - Golden Syrup (7:13pm)
5th: 7 - Caster Sugar (7:22pm)
6th: 2 - Glucose Syrup (7:35pm)




From the back, at 7:53, you can see the mixtures with their varying amounts of foam. Control is a little hard to see but you may be able to make out the fact that there was no reaction at all without a sugar substance.

5 - Brown Sugar did not pop up, but by 9:07pm I was able to gently stand it upright.

9:07pm - Brown Sugar balancing upright, despite not being fully pressurised at this point (as you can see - it is wrinkly around the edges).

By 10:51pm last night, 4 hours and 8 minutes after the experiment began, the balloons had reached the extent of their expansion and the real result of the experiment could be observed: which sugar produced the most respiration, and thus the most gas?

10:51pm: results are in!

As you can see, Glucose Syrup was far and away the most successful substance, producing twice as much gas as any of the others. This was the final tally:

1st: 2 - Glucose Syrup
2nd: 7 - Caster Sugar
3rd: 3 - Golden Syrup
4th: 8 - Icing Sugar Mixture
5th: 6 - White Sugar
6th: 4 - Honey
7th: 5 - Brown Sugar

Table: Rankings of Sugar Types

The most obvious thing I discovered in this experiment is that brown sugar is clearly not a good medium for producing respiration in yeast. It performed very poorly.

Excluding brown sugar and the control, a very interesting pattern emerges in the data. White Sugar, Icing Mixture and Honey were 1st, 2nd and 3rd in the order of inflation, but were 5th, 4th and 6th respectively in the amount of gas they produced. On the other hand, Golden Syrup, Caster Sugar and Glucose Syrup were 4th, 5th and 6th in popping up, but 3rd, 2nd and 1st respectively in the amount of gas they produced. This suggests that a fast reaction is not necessarily going to produce the most gas; and in fact that the substances that took a little longer to get going produced more gas in the long term. One could postulate that this is because the substances that were quick to get going were used up before large quantities of gas could be produced?

Glucose was clearly the outstanding winner for producing sustained, regular respiration in yeast: it was slow to get going, but did not peak early and taper off the way the faster substances did.

Although my experiment was completed at this stage, I decided to leave it in place overnight, partly due to laziness and partly to see what would happen.

The Morning After

As you can see, Glucose (most gas) and White Sugar (first to inflate) remained inflated to an extent, although less than they were at their peak. The others had deflated and fallen down. I'm not sure why they did so, whether it was leakage or the gas was reabsorbed, or some other explanation.

But I'm not looking forward to opening them all up and filling my house with the smell of sugary yeast!


Great pictures! You could call it"The Rainbow Sugar Experiment". Good name for a book, isn't it!

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