Bread is one of the common household products prepared using microbes.
Important points
- The dough used for making bread is fermented using baker’s yeast.
- Baker’s yeast is a fungus belonging to the class Ascomycetes, and its scientific name is Saccharomyces cerevisiae.
- Bread appears porous due to the formation of CO2 during alcoholic fermentation by Saccharomyces.
NCERT: the dough used for making foods such as dosa and idli is also fermented by microbes (bacteria), and its puffed-up appearance is due to the production of CO2 gas. Similarly, the dough used for making bread is fermented using baker’s yeast (Saccharomyces cerevisiae).
Alcoholic fermentation in bread making
Yeast breaks down the sugars in the dough without oxygen, producing ethanol and carbon dioxide:
Alcoholic fermentation
C6H12O6 → 2C2H5OH + 2CO2 + energy
(glucose → ethanol + carbon dioxide)
- The CO2 gas gets trapped in the dough as small bubbles, making the dough rise and giving bread its soft, spongy texture.
- The small amount of ethanol formed evaporates during baking.
- Baking also kills the yeast cells.
About baker’s yeast
- Saccharomyces cerevisiae is a unicellular fungus.
- It reproduces asexually by budding.
- It can respire aerobically when oxygen is available, and carries out alcoholic fermentation when oxygen is absent.
The same species, Saccharomyces cerevisiae, is used for fermenting malted cereals and fruit juices to produce ethanol – NCERT calls it brewer’s yeast in this role. Compare with cheese, another food made using microbes: Swiss cheese gets its holes from CO2 made by a bacterium, Propionibacterium.