Introduction
The tension is palpable. Under the warm glow of heat lamps, tiny yeast cells spring into action. They’re racing—not in cars, but to turn sugars into energy and carbon dioxide in a process called fermentation. This is no regular race, but rather a high-stakes sprint between life and death. The competitors? Tiny organisms called yeast eagerly run against the clock to get the energy they need to survive. This race is known as yeast fermentation, a process humans have relied on for centuries. It fuels many things, from the bread on our tables to the beer in our glasses.
For thousands of years, bakers and brewers used yeast as an agent to harness this race, all while not knowing it was alive. Today, we know that yeast is a complex living organism composed of cells that are eukaryotes—much like the cells of humans! Eukaryotes contain a nucleus, where genetic information is stored as DNA. They also contain tiny structures called organelles that are responsible for performing certain functions. A well-known example is the mitochondria, the cell’s engine. Mitochondria are important organelles needed to generate the energy required for our cells to function.
Like a car needs gas, yeast cells need fuel to run. By using sugar as a fuel source, yeast can produce the necessary energy through fermentation.
Fermentation
When yeast meets sugar, it sparks a chemical reaction that increases the rate of carbon dioxide production, causing the dough to rise and giving bread its characteristic fluffy texture. To understand how fermentation powers this race, we need to examine its biological nature. Fermentation consists of two stages, each serving a distinct purpose. The first is called the primary step, where yeast begins to metabolize or break down sugars, releasing carbon dioxide and alcohol. Though short, primary fermentation requires ideal conditions for yeast to activate its metabolic processes efficiently.
Next up is secondary fermentation, which is relevant to brewing. Unlike the primary step, secondary fermentation typically spans days to weeks. During this time, the alcohol content gradually increases as yeast processes sugars. Interestingly enough, this rise in alcohol is counterproductive to yeast growth, as high concentrations of ethanol create a harsh environment that inhibits their activity. The alcohol denatures proteins within the yeast cells, disrupting their structure and function. Eventually, the concentration could get excessive and begin destroying yeast cells.
What Sugar Is Best
There are many types of sugars with different characteristics, impacting the efficiency of yeast. David Georges, a current undergraduate student at UC San Diego, aimed to answer the question: What type of sugar is best for yeast fermentation? This project started as a simple high school assignment where he was assigned to write a paper on a hypothetical research question. However, due to his interest in the topic, he decided to pursue it further in collaboration with a biology teacher at JFK High School, who provided the necessary equipment. This experiment compared the sugars glucose, fructose, sucrose, maltose, and lactose. Georges hypothesized that glucose would be the best source for yeast fermentation, considering its relatively simple structure.
In this study, Georges used Saccharomyces cerevisiae, better known as brewer’s yeast, because it is commonly used in brewing and baking. This species was a controlled component of the study, meaning it was used in all trials of the experiment. This reduces variability in the result as the species of yeast won’t be a factor impacting carbon dioxide production.
The experimental methods focused on determining the impact of different sugars on the fermentation rate of Saccharomyces cerevisiae by measuring carbon dioxide production. To begin, a yeast solution was prepared using a consistent concentration of yeast (3.5%) in tap water maintained at a temperature of 32–35°C. Enzymes, or proteins that speed up reactions, work best at this range, which is why this temperature range is optimal for fermentation. A magnetic stir bar was used to mix the solution, ensuring aeration (or the introduction of air) and even distribution of yeast and sugar. Each sugar was introduced into the yeast solution in two phases: an initial 2.0-gram portion followed by a second 2.0-gram portion after one hour to activate the yeast. After activation, 20 mL of each sugar-specific yeast solution was placed into fermentation tubes and incubated for 12 minutes at a constant temperature within the optimal range. The yeast was then studied to see how much carbon dioxide was released within the tubes. All conditions, including sugar concentration, incubation time, and equipment, were kept the same across all trials to ensure consistency. The process was repeated for each sugar type, with results recorded and compared to determine the efficiency of fermentation for each sugar.
Results
The results of this experiment were consistent with Georges’s hypothesis that glucose is the best sugar source, confirming that sugar type does impact the fermentation rate. Glucose had the greatest amount of carbon dioxide production, with an average displacement of 4.08 mL. In this study, the displacement is the volume of carbon dioxide gas produced during fermentation. The other three sources were noticeably smaller, with fructose and sucrose causing a displacement of 3.18 mL and 2.92 mL, respectively. The third smallest fermentation level was maltose at 2.62 mL. The sugar with the smallest displacement of 0 mL on average is lactose. Why? Because yeast is ‘lactose intolerant’. Research published in the Taylor and Francis journal found that yeast doesn’t have the enzyme lactase, so it can’t break down lactose, meaning no carbon dioxide can be produced.
Discussion
Georges’s findings are supported by prior research conducted at the University of British Columbia (UBC). Both studies identified glucose and fructose as the highest carbon dioxide producers among different sugar sources. Although the UBC study did not find a statistically significant difference in the carbon dioxide production of glucose compared to other sources, David’s work did. As such, the results weren’t due to random chance.
Some limitations to Georges’s study could explain the result. The experimental design of this study required the fermentation tubes to be exposed to air for a few seconds before closing the incubator door. Although this timespan is very short, possible outside contamination of the sources could have occurred, altering the data collected. Additionally, yeast samples were introduced into the fermentation tube outside of the incubator. This means the fermentation process occurred before incubation, causing a premature buildup of carbon dioxide. This could have skewed the results as well. Given these limitations, the researcher proposes implementing data collection changes, including only testing one tube at a time, to reduce outside exposure and to ensure accurate data collection.
Conclusion
Just like in a race, the right fuel makes all the difference. Though yeast may be small, its ability to rapidly convert sugars into energy has powered human life in many ways. Beyond the kitchen, this study underscores yeast’s critical role in renewable energy production. According to researchers at the University of Malaya, brewer’s yeast is efficient at ethanol production, which is an essential component of biofuels. Georges’s study used the same type of yeast and provided evidence that glucose was the best source in fermentation. Thus, in the future, yeast fermentation can be harnessed on a large scale to produce sustainable energy. In the grand race of fermentation, yeast speeds ahead, fueled by sugars. But, in our own races, yeast may soon be fueling our engines too.
