Group of chemical reactions induced by microorganisms or enzymes that split complex organic compounds into relatively simple substance

Anaerobic conversion of sugar to carbon dioxide and alcohol by yeast


       Available – varying sizes – total volume capacity

       Small laboratory fermentors – 1 – 15 lts

       Pilot plant fermentors – 25-100-2000 gallons

       Range – 5000 – 10,000 gallons

       Actual operating volume – less than that of total volume

       Head space – top – above the liquid medium – splashing, foaming and aeration

       Head space – a fifth to a quater

Fermentor Design

     Fermentor – strong enough to withstand the pressure of large volumes of aqueous medium

     Fermentor vessel – capable of operating aseptically – number of days

     Adequate aeration and agitation – provided – meet the metabolic requirements of m/o – mixing should not damage the organism

     Power consumption should be as low as possible

     A system of temperature control should be provided

     A system of PH control should be provided

     Sampling facilities – provided

     Evaporation losses = not excessive

     Additional inoculum or seed tanks – small sized Fermentor – inoculum is produced – added directly to the fermentor

      Drain or mechanism – bottom of fermentor – remove the completed fermentation broth

     Vessel should be designed – require minimal use of labour in operation, harvesting, cleaning and maintenance

     Smooth internal surfaces

     Material of vessel – withstand repeated steam sterilization cycles

     Small scale – Glass or stainless steel

     Glass –smooth surfaces, non-toxic, corrosion proof and easy to monitor

Fermentor Design




       Air dispersion

       Oxygen transfer

       Heat transfer

       Maintain uniform environment throughout the vessel

       Enhancement of mass transfer between dispersed phases



       Four baffles to eight  – incorporated – vessel – prevent vortex – improve aeration efficiency

       Metal strips roughly one tenth of vessel diameter – attached radially to the wall

       Baffle should be installed – gap between the vessel wall  and baffle – scouring action – minimizes the microbial growth on the baffles and fermentor walls

Sparger – Aeration System

       Device – introducing air – liquid – Fermentor

Three types

  1. Porous sparger
  2. Orifice sparger
  3. Nozzle sparger

       Pipe – minute holes

       Hole size – 1/64 – 1/32 inch or larger

       Allows air under pressure to escape as tiny air bubbles into the liquid medium. Small size hole – requires great air pressure

Sterilization of Air Supply for Fermentation

       Sterile air – large volumes – aerobic fermentation process

       Heating and filtration – main methods of sterilization

       Heating is generally too cost for full scale operation

       Glass wool, glass fiber – filter material

Cooling Coil

       Temperature – important factor

       High temperature – ferments – destroyed

       Very low temperature – reaction – slow

       Optimum temperature – maintained

       Growth temp of M/o —– may or may not coincide with optimum temp of fermentation

       To maintain optimum temp – fermentor should be cooled

       Passing cold water –inside wall of tank or jacketed walls of tank

Sterile Filter

       Sterilization of air – entering fermentor – sterile filter

       Composed cotton wool – trap m/o in air

       Form the filter – air – carried through sterile piping – bottom of the fermentor – beneath the impeller blade


       Aeration and agitation – liquid medium – foam – if media containing protein or peptides

       Not controlled –raise to headspace – tank – along with spent air

       Condition may cause – contamination  and limits the gas exchange between the medium and the atmosphere of the head space

       Antifoaming agents – Lowers the surface tension and decreases the stability of the foam bubbles – burst

       Two types

       Inert antifoam agents – Silicone compounds

       Too expensive – adv – Not utilized by m/o and non-toxic

       Antifoams – crude organic materials – animal or vegetable oils – Lard oil, corn oil and soyabean oil or long chain alcohols like octadecanol

       Not inert, toxic, provide additional nutrients to the m/o

       Fatty acid of the antifoam – lower the PH of the medium

       Added – manually or automatic

       Automatic – sensing mechanism used – foam risen into headspace of fermentor – product touches the electrode – current produced – activate pump to add antifoam agent

Sterilization of Medium

       Pure culture fermentation – medium to be sterilized

       Small scale – medium placed directly – fermentor – autoclaved

       Large tanks – not feasible

       Medium+ water – — pumped into retention tubes and heat exchangers before passing into fermentation tank

       Retention tube contain  – steam jet heaters – inject high pressure steam in to the medium  – to sterilize it as it passes through the pipes

       Rate of passage – adjusted – provide complete media sterilization without overcooking


       Anaerobic conversion of sugar to carbon dioxide and alcohol by yeast

       Fermentor vessel



       Cooling coil

       Antifoam agent

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