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leiva-pärmkottseen

Page history last edited by PBworks 17 years, 4 months ago

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leiva-pärmkottseen (Saccharomyces cerevisiae) taignakergitaja, alkoholkääritaja, kommunaalreovete tavaline asustaja.

Saccharomyces cerevisiae

Beer is proof that God loves us and wants us to be happy.

Benjamin Frankin

 

Sometime between 10,000 and 15,000 years ago, a Mesopotamian farmer discovered that the water some grain had been soaking in had developed a funny taste. He woke the next day having made two important discoveries:

 

Beer

Hangovers

The first written records of brewing come from Sumeria about 6,000 years ago. But all that drinking was making people hungry, so in Egypt around 5,000 years ago, they starting making bread (or at least, wrote down the recipe). Before that, bread was tough, dry stuff that tended to break your teeth and made your jaw ache. Bread made with yeast was wonderful, light, tasty stuff. The secret? Saccharomyces cerevisiae:

 

Saccharomyces cerevisiae (Yeast) (1.6Mb Quick Time web quality sample: download FREE Quick Time Player)

You can get a longer, better quality version of this video on the Microbiology Video Library CD.

Broadcast quality (520 line) digital video: 4 minutes duration, no soundtrack. Supplied on PAL format miniDV tape plus accompanying notes.

If you are interested in obtaining this video, please contact us.

 

 

 

Bread dough rising (yeast action) (1.2Mb Quick Time web quality sample: download FREE Quick Time Player)

Time-lapse: speeded up 60 times.

You can get a longer, better quality version of this video on the Microbiology Video Library CD.

Broadcast quality (520 line) digital video: 1 minute 30 seconds duration, no soundtrack. Supplied on PAL format miniDV tape plus accompanying notes.

If you are interested in obtaining this video, please contact us.

 

 

 

Yeasts such as Saccharomyces cerevisiae are single-celled fungi which that multiply by budding, or in some cases by division (fission), although some yeasts such as Candida albicans may grow as simple irregular filaments (mycelium). They may also reproduce sexually, forming asci which contain up to eight haploid ascospores. If you look closely at the video, you can see examples of budding cells (arrow, left). Saccharomyces cerevisiae has thick-walled, oval cells, around 10 µm long by 5 µm wide.

 

 

Fermentation:

Saccharomyces cerevisiae is commonly known as "bakers yeast" or "brewers yeast". The yeast ferments sugars present in the flour or added to the dough, giving off carbon dioxide (CO2) and alcohol (ethanol). The CO2 is trapped as tiny bubbles in the dough, which rises.

 

Why does yeast do this?

To gain energy from the breakdown (fermentation) of carbohydrates, as in the diagram opposite.

The fermentation of beer and wine was originally caused by naturally occurring yeasts present in the environment. Some wineries still use natural yeast strains, however most modern brewers use highly cultured isolates, e.g. Saccharomyces carlsbergensis, named after the Carlsberg Brewery in Copenhagen. The bubbles in sparkling wines such as Champagne are trapped CO2, the result of yeast fermenting sugars in the grape juice. One yeast cell can ferment approximately its own weight of glucose per hour, giving rise to large volumes of CO2!

 

 

 

 

Fungal Biology: Understanding the Fungal Lifestyle

by D.H. Jennings, G.Lysek.

A concise introduction to the fundamental properties and activities of fungi in their natural environment. This approach avoids the repetition of taxonomy and life cycle studies found in similar texts. The environmental perspective used to illustrate the book helps readers develop their understanding of basic principles.

(Amazon.co.UK)

 

 

 

 

Introduction to Modern Mycology

by J.W. Deacon.

Provides students of microbiology, mycology and biology with an introduction to fungi. Emphasizes the behaviour, physiology, activities and practical significance of fungi, and includes extensive sections on fungal pathogens of plants, animals and humans, the roles of fungi in major environmental processes, the use of fungi as biological control agents of pests and pathogens, fungal cell biology, and the application of fungal molecular genetics. Contains numerous photographs, line drawings, and diagrams.

(Amazon.co.UK)

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