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Flashcards in Microorganisms Deck (27):

What 2 problems can develop if the inside of the fermenter and the new nutrients are not sterile

1) any bacteria or funghi that managed to get in would compete with the organism in the culture, reducing the yield of product
2) the product would become contaminated with waste products or cells of the 'foreign' organism


Aseptic precautions in fermentation

Filtering the air
Sterilising the fermenter


Purpose of water jacket in fermenter

Fermentation produces heat, so prevents contents from overheating and keeps the temperature at the best level for growth (optimum temperature for enzymes)


Why do fermenters have to be made of materials which will not corrode

Many microorganisms produce acidic waste products


How is the fermenter cleaned

With very hot steam under high pressure


Purpose of paddles in fermenter

Mix up contents -> keeps microorganisms in suspension in the liquid, so that they get more exposure to the nutrients, and helps keep the temperature even throughout the vessel



The use of living organisms to make useful chemicals and products or to perform an industrial task


Why is it better to sterilise the fermenter with steam rather than disinfectants

Disinfectants are difficult to wash out of the fermenter and might kill the microorganism being grown


What process occurs when yeast is added to glucose and oxygen and why is it useful

Aerobic respiration
The carbon dioxide produced is used to make bread rise


What process occurs when yeast respites in absence of oxygen

Anaerobic respiration (fermentation)


Purpose of malting

Breaking down the starch in barley to sugars so that the yeast cells can ferment it to ethanol


Role of amylase in beer production

When barley grains germinate it produces amylase which breaks down the starch into maltose


How are barley seeds germinated

By soaking in water and laying them on a flat surface in a malthouse


Why is malt ground up and mixed with water in a mash tun

Activates the enzymes to concert starch into maltose


Why are hops added to beer

To give it its flavour and stop bacteria growing


What happens after the hops and yeast are added

Beer is centrifuged, filtered, and sometimes pasteurised
It is then put into casks or barrels


What is yoghurt

Milk that has been fermented by lactic acid bacteria


What happens in lactic fermentation

Lactose -> lactic acid


Effect of lactic acid on milk

-gives it a low pH which causes milk proteins to denature and curd is formed
-acidic conditions also prevent harmful bacteria from growing


Why is milk pasteurised at 85-95*C for 15-30 mins

To kill off any natural bacteria it contains


Why is milk homogenised

To disperse the fat molecules


Why is milk cooled to 40-45*C before being inoculated with a starter culture of lactic acid bacteria?

It's the optimum temperature for bacteria


What happens when the milk is inoculated with a starter culture of lactic acid bacteria

-bacteria digest milk proteins and ferment lactose to lactic acid
-the pH falls to around 4.4
-the mixture thickens as the drop in pH causes the milk proteins to coagulate


Why is the fermenter sterilised

To prevent competition from unwanted organisms and to prevent chemical contamination of product


Why is wine no more than 14% alcohol

High concentrations of ethanol kill the yeast cells


Why does fermentation eventually stop in yoghurt production

The drop in ph reduces the growth of lactic acid bacteria


Making yoghurt is a way of preserving nutrients from milk how?

Low pH prevents growth of 'spoiling' microorganisms