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



       Agitation  -

       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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