Fermentation

Fermentation

1. It is a process used to produce alcohol e.g. beer and wine. The microbe used is yeast

2. Main stages of fermenting yeast

   • 1. Extract sugar
     • 2. Add yeast
       • 3. Adjust temperature for yeast growth
         • 4. Ferment mixture into airtight container to prevent entry of air and microorganisms
           • 5. Clarify beer (makes yeast settle)
             • 6. Draw out the alcohol
               • 7. Pasteurise and bottle the beer

3. The breakdown of sugar by yeast in the absence of oxygen = anaerobic respiration

   • sugar -> ethanol + carbon dioxide + energy
     • C6H12O6 -> 2C2H5OH +2CO2
       • If oxygen is present = aerobic respiration
         • sugar + oxygen -> water + carbon dioxide

4. Yeast and Alcohol

   • Different strains of yeast give alcohol different flavours and strengths
   • Usually the high concentration of alcohol produced by the yeast cells kills them making the drink safe for humans
   • Yeast that can tolerate high levels of alcohol are used to produce drinks with a higher alcohol content e.g. vodka

5. Effect of temperature on yeast

   • For every 10 degree celcius rise, the yeast doubles
     • Until it reaches the optimum and then the yeast decreases
       • This is because the enzymes are denaturing