Friday, August 26, 2016

Yeast, Coke, and Sugar Water

I'm taking a high school biology class, and one of the assignments for this class was to design an experiment involving yeast and three liquids with three different sugar concentrations. For the first experiment, I chose Diet Coke, regular Coca-Cola, and the real-sugar Coke Life and put 1/4 ounces of yeast into each soda. There was a balloon attached to each bottle and at certain intervals, that balloon was measured to get an idea of how much carbon dioxide the yeast had produced. Now, I know that a lot of people who follow me on the Twitterverse are strongly anti-Coke because they use plastic. I know that plastic and Coke bottles are really, really bad for sea life. After liquids were emptied out of the bottles, the bottles were put in the recycling bin. Anyway, here's my data.

Diet Coke
Regular Coca-Cola
Coke Life
Anyway, my hypothesis was that Coke Life would have the most growth, even though regular Coca-Cola had more sugar because, as I theorized, the yeast had evolved to eat sugar, not high-fructose corn syrup. I was wrong. Diet Coke seemed to produce the most gas before it stopped, but in the graphs, regular Coke was pretty much identical to Coke Life. And I had not expected Diet Coke, which contains no sugars at all, to have any growth. As it turns out, the balloon was being inflated by residual carbon dioxide from the soda and not from the fermentation. And about the extreme jumps in Regular Coca-Cola and Coke Life, it's because until 1 hour, I was recording the radius of the balloon, not the volume. OOPS! But the radius was correct.

To try to remove the external variables involved in doing Coke (like artificial colors, caffeine, and carbonation), I did a second experiment with just water and the same concentrations of sugars as the Coke. It worked much more as I had expected the Coke experiment to work. Here is my data from that experiment.

0 grams of sugar
7 grams of sugar
11 grams of sugar
Apparently it isn't more sugar that impacts the yeast growth. Apparently there's a "sweet spot" (pun intended) around 7 grams that seems to provide optimum yeast growth. Stay tuned for experiments including stuff like how yeast react to artificial sweeteners, brown sugar, and other sweeteners. 

1 comment:

  1. Cool! For another control experiment why don't you try soda water (fizzy water, agua con gas)? It should show only the growth due only to the residual carbonation.

    Now if you add the data from the soda water and the sugar water at the same concentration as coke do you get the same curve as coke? (You'll have to compare volumes here because it doesn't make sense to add circumference since it is not linearly related to volume). Maybe - maybe not, different brands of soda water have different concentrations of dissolved CO2 in them (San Pellegrino has a lot for instance). But different kinds of Coke have different levels of carbonation too - Diet Coke has more.

    (Long time reader, first comment. Great blog!)