Bacteria and making yoghurt

• what is fermentation?

  • fermentation - microorganisms break sugars down to release energy through anaerobic respiration
• how is yoghurt made?

  • equipment is steralised to kill off any unwanted microorganisms
  • milk is pasturised (heated to 72 degrees for 15 secs) to kill harmful microorganisms - milk is cooled
  • lactobacillus added - mixture incubated (heated to 40 degrees) in a fermenter
  • the bacteria ferment the lactose sugar in the milk to form lactic acid
  • lactic acid causes milk to clot - solidify into yoghurt
  • flavours and colours added as yoghurt is packaged
• What do fermenters provide for microorganisms to grow?

  Liquid culture medium with nutrients
• Why is pH monitored in fermenters?

  To keep enzymes working efficiently
• How does maintaining optimum pH affect fermentation?

  It keeps reaction rates and product yield high
• What is used to prevent overheating in fermenters?

  A water-cooled jacket
• What happens if enzymes denature in fermenters?

  They lose their ability to catalyze reactions
• How are vessels sterilized between uses?


  With superheated steam
• Why are aseptic conditions important in fermentation?

  They prevent contamination and increase product yield
• How is oxygen supplied to microorganisms in fermenters?

  By pumping sterile air into the vessel
• Why do microorganisms need oxygen for respiration?

  To provide energy for growth
• How are microorganisms kept in contact with fresh medium?

  By paddles that circulate the medium around the vessel
• What is the effect of circulating the medium on product yield?

  It increases product yield as microorganisms can always access nutrients needed for growth