What indicates a positive result in yeast fermentation test?

What indicates a positive result in yeast fermentation test?

• A. Growth
• B. pH change
• C. Color change
• D. Gas bubbles

Answer: (D)

In a yeast fermentation test, the key signal is gas production from sugar fermentation. Yeast can ferment sugars anaerobically, producing ethanol and carbon dioxide. A Durham tube traps any gas formed, so visible gas bubbles inside the inverted tube show that fermentation occurred. Growth alone just shows viability and doesn’t prove fermentation; pH change or color shifts can result from other metabolic activities and aren’t definitive proof of fermentation with gas production. The gas bubbles provide the most direct, unambiguous indication of a positive result.

In a yeast fermentation test, the key signal is gas production from sugar fermentation. Yeast can ferment sugars anaerobically, producing ethanol and carbon dioxide. A Durham tube traps any gas formed, so visible gas bubbles inside the inverted tube show that fermentation occurred. Growth alone just shows viability and doesn’t prove fermentation; pH change or color shifts can result from other metabolic activities and aren’t definitive proof of fermentation with gas production. The gas bubbles provide the most direct, unambiguous indication of a positive result.