Does yeast produce the same amount of gas from every type of sugar? Yeast breaks down sugars through fermentation (a process that releases carbon dioxide). Not all sugars have the same structure, and yeast is picky about which ones it can use. You dissolve different carbohydrates in water and adjust the pH to 6.5. After adding yeast you 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. The results show that yeast prefers sugars with structures similar to sucrose.