Fermentation
Fermentation is how yeast turns sugar into gas and alcohol without using oxygen.
Yeast cells are small circles packed inside a sealed jar of sugar water. Each cell takes in sugar and pushes out a gas bubble and a drop of alcohol. The bubbles rise to the top of the jar, and the liquid slowly changes as the sugar gets used up. No air enters the jar; the whole process runs on sugar alone.
Explaining fermentation by grade level
Yeast is a tiny living thing that eats sugar. When you mix yeast with sugar water, it makes a gas. That gas fills up a bag or blows up a balloon. The yeast does this all on its own, with no heat needed.
Projects that explore fermentation
When yeast runs out of oxygen but still has sugar to eat, it switches to fermentation — producing alcohol and carbon dioxide instead. You seal dried baker's yeast and crushed grapes together in a plastic bag, so the yeast uses grape sugar as a substrate, yielding carbon dioxide and ethanol. A pH strip taped inside tracks acidity changes as the juice turns more acidic. Gas fills the bag and foam appears.
Yeast cells are living organisms that eat sugar and release carbon dioxide gas — the same gas that makes bread dough rise. You dissolve a packet of rapid-rise yeast in lukewarm water, stir in half a cup of sugar, and pour the mixture into a large freezer bag sealed tightly. After about an hour in a warm spot, the bag puffs up. Billions of cells working together produce enough gas to see and feel.
Yeast is a living organism that performs fermentation, turning sugar into alcohol and carbon dioxide. Damage the yeast cells and that process slows. This experiment shines UV light on yeast mixed with apple juice, then measures how much CO2 pushes out of an upside-down water-filled cylinder every 10 minutes. The UV-exposed yeast produced no gas for the first 20 minutes, then fermented at a slower rate.
Fermentation needs sugar as fuel. Yeast turns that sugar into gas and alcohol. Juices with more sugar produce more fermentation, which is why orange juice fermented the most in this test.
Not all sugars work equally well as fuel for fermentation. You dissolve different carbohydrates in water, adjust the pH to 6.5, add yeast, and warm the mixture to 37.5 degrees Celsius. An upside-down water-filled cylinder collects the CO2 so you can measure its volume. Sugars like sucrose and glucose produce lots of gas. Others like galactose and lactose produce almost none, showing that yeast is selective about which sugars it can use.