Fermentation is a technique used to produce various foods through the metabolic process of microbes. It involves microorganisms like yeast and bacteria converting carbohydrates into alcohol and acids. Common fermented foods include wine (from grapes), beer (from malted barley), soy sauce (using fungus Aspergillus oryzae), yogurt and cheese (lactic acid bacteria), and bread (from yeast fermenting sugars). Fermentation allows production of diverse foods and offers benefits like food preservation through the antimicrobial acids generated.

1. FERMENTATION: TECHNIQUE
USED FOR THE PRODUCTION OF
FOOD BY MICROBES
PRESENTED BY: AYESHA KABEER
UNIVERSITY OF SIALKOT

2. Alcoholic Fermentation in
General:
• Fermentation is a chemical conversion of
carbohydrates into ethanol and carbon
dioxide.
• When oxygen is absent, the yeast switches to
anaerobic cell respiration aka fermentation
1. Wine and Beer production:
Saccharomyces cerevisiae is involved in wine and
beer production

3. Wine production
• Crush grapes to make juice, place into vessels or
vats
Yeast cells naturally present on the grapes
Selected varieties of yeast added to give special
flavor
• 2. Few days later the oxygen in the juice is used
up
Yeast cells respire anaerobically
• 3. Fermentation ends, Wine produces
When all the sugar in juice is used up
When ethanol content reaches 15%

4. Beer production:
• Barley grains germinate
AMYLASE is produced
• Barley seeds dried after few days
Kill them and preserve the amylase
dried, semi-germinated barley seeds= MALTED
BARLEY
• Mix malted barley with other sources of starch,
selected variety of yeast and water into a vat
Hops added for flavoring
amylase from malted barley digests starch to
release MALTOSE
Yeast converts to ethanol (anaerobic cell
respiration)

5. Soy sauce production:
• It takes 6 months to make soy sauce.
• It involves a fungus called Aspergillus Oryzae
Lactic acid fermentation by
lactic acid bacteria:
• Tastes of yogurt, pickles, sharp cheeses and
some sausages due to production of lactic acid
by lactic acid bacteria

6. • Can be made from milk of wide variety of animals
Cow’s milk most common
• Cheeses classified as very hard, hard, semi-soft and soft
Classification passed on percentage of water content
Cottage cheese easiest cheese to make
Pasteurized milk inoculated with starter culture
Culture causes milk proteins to coagulate
Coagulated proteins called curd
Curd heated and cut into small pieces to facilitate
drainage of liquid waste termed whey
Cheese production:

7. • Most other cheeses undergo further microbial
processing termed ripening or curing.
• Enzyme rennin is added to fermenting milk to hasten
protein coagulation
• Curds salted after whey is separated and pressed and
ripened to encourage changes in texture and flavor
• Ripening can take weeks to years
• Longer ripening produces more acidic sharper
cheese
Certain organisms produce certain characteristics
»Propionibacterium shermanii  Swiss cheese
»Penicillium roquefortii  Roquefort, and
gorgonzola
Cheese production:

8. • Pasteurized milk is concentrated slightly then
inoculated with starter culture
• Mixture is incubated for several hours at 40° C - 45°
C for several hours
• Thermophilic bacteria grow rapidly at higher
temperatures
• Produce lactic acid and other end products
• Contribute to flavor
• Controlled incubation ensures proper levels of acid
and flavor compounds
Yogurt production:

9. • Vinegar: Aqueous solution of at least 4% acetic acid
• Product of oxidation of ethanol
• Strictly aerobic process
• Fermenting bacteria are obligate aerobes
• Organisms can tolerate high concentration of acid
• Vinegar generator produces available oxygen to
hasten oxidation
• Sprays alcohol on biofilm of acid bacteria on wood
chips
• Alcohol trickles down and is oxidized by bacteria
Vinegar production:

10. Bread production:
• Bread rises due to carbon
dioxide produced through
fermentation of sugars by
baker’s yeast
• Any alcohol produced evaporates
during baking
• Characteristic flavor of sour
dough bread due to the addition
of lactic acid bacteria to bread
making ingredients

11. Benefits of fermentation:
• Acid produced in yogurt, cheese, and pickled
vegetables inhibit growth of many spoilage
organisms and foodborne pathogens
• Fermentation historically important method of
food preservation

12. Conclusion:
• Through fermentation technique, different
types of food products can be obtained
• For example: cheese, soy sauce, wine, beer,
yoghurt, pickles, bread, vinegar etc.