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Yeasts are the single celled growth forms of most fungi. Yeasts are unicellular fungi. They are heterotrophic organisms that require organic carbon as there common source of energy or carbon. Most yeast cells are facultative anaerobes and they are able to grow even in the absence of oxygen. Many yeast cells especially Saccharomyces cerevisiae are important industrial microorganisms because of the important roles that they play in the production of foods and other products of economic importance. Most yeasts exhibit dimorphism, a phenomenon in which a fungal cell exhibit two growth forms i.e. the yeast form and the filamentous (mould) form. Only few types of yeast such as Cryptococcus neoformans (which causes a rare form of meningitis) and Candida albicans are animal/human pathogens.

Saccharomyces cerevisiae is a species of yeast that is also called the baker’s yeast. It is one of the most useful yeast because it has been used in baking and brewing since ancient times. S. cerevisiae cells are usually round to oval in shape, and they measure about 5-10 µm in diameter. S. cerevisiae reproduce asexually by a process known as budding – in which daughter cells are produced as off-shoots of a parent cell by a process known as budding. Yeasts can also reproduce sexually, and this usually involves two mating haploid yeast cells. Yeasts are common in the environment and are isolated from sugar rich materials such as palm wine and food products high in carbohydrates. Brewer’s yeast, ale yeast, top fermenting yeast, baker’s yeast and budding yeast are other names that S. cerevisiae is known for; and these names connotes to the different applications of the organism in the production of a wide variety of economically useful products. S. cerevisiae can grow aerobically on simple carbohydrate sources such as glucose, and maltose. They use ammonia and urea as their sole nitrogen source.

Yeasts also require phosphorous and some minerals for their optimal growth. S. cerevisiae has a short generation (doubling) time which is about 1-2 hours, and they can be easily cultured in vitro in the laboratory. These characteristics accounts for their use and preference as the major source of nutritional yeast and yeast extract for most of the fermentation processes in the industry. S. cerevisiae has a small size; and they can be easily manipulated or transformed in the laboratory for increased yield of their metabolite. Yeast cells have a short generation time; and they can be easily accessed or cultured on simple culture media such as Sabouraud dextrose agar (SDA). Their growth requirement can easily be obtained; and S. cerevisiae has tremendous economic benefits, which is why they are the most preferred yeast for fermentation processes.


  • They are used in brewing beer.
  • They are used in baking bread.
  • Yeasts are used in wine fermentation.
  • They are used for the industrial production of ethanol and other industrial fuels.
  • Yeasts such as S. boulardii are used in the production of probiotics used to maintain the health of the gastrointestinal tract.
  • Yeasts convert sugars to carbon dioxide (CO2) and ethanol; and can be used to generate CO2 to nourish plants in aquariums.
  • Yeasts also cause food spoilage.

Further reading

Bushell M.E (1998). Application   of   the   principles   of   industrial   microbiology   to   biotechnology (ed. Wiseman, A.) Chapman and Hall, New York.

Byong H. Lee (2015). Fundamentals of Food Biotechnology. Second edition. Wiley-Blackwell, New Jersey, United States.

Frazier W.C, Westhoff D.C and Vanitha N.M (2014). Food Microbiology. Fifth edition. McGraw-Hill Education (India) Private Limited, New Delhi, India.

Jay J.M (2005). Modern Food Microbiology. Fourth edition. Chapman and Hall Inc, New York, USA.

Bushell M.E (1998). Application   of   the   principles   of   industrial   microbiology   to   biotechnology (ed. Wiseman, A.) Chapman and Hall, New York.

Farida A.A (2012). Dairy Microbiology. First edition. Random Publications. New Delhi, India.

Nduka Okafor (2007). Modern industrial microbiology and biotechnology. First edition. Science Publishers, New Hampshire, USA.

Roberts D and Greenwood M (2003). Practical Food Microbiology. Third edition. Blackwell publishing Inc, USA.

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