Microbes in Human Welfare

Lesson

Part 1 — microbes are not only germs: many make our food, drinks, medicines and industrial chemicals.

In this lesson you will

Give examples of microbes used to make household foods
Name microbes used to produce beverages, antibiotics, acids and enzymes
Describe bioactive molecules such as streptokinase, cyclosporin A and statins

Concept

Microbes in household products

Fermentation by microbes changes the taste, texture and nutrition of foods.

Table of household products with the microbes that make them
Product	Microbe	What it does
Curd	Lactic acid bacteria (Lactobacillus)	Produce acids that coagulate and partly digest milk proteins; increase vitamin B₁₂; check disease-causing microbes in the stomach
Dosa and idli dough	Bacteria	Fermentation releases CO₂, which puffs up the dough
Bread dough	Baker’s yeast (Saccharomyces cerevisiae)	Fermentation releases CO₂ that makes the dough rise
Toddy	Microbes in palm sap	Ferment the sap into a traditional drink
Swiss cheese	Propionibacterium sharmanii	CO₂ makes the large holes
Roquefort cheese	Specific fungi	Ripening gives a particular flavour

Worked example

Worked example 1: what makes the dough rise?

Two bowls of bread dough are kept warm. Bowl A has yeast; bowl B has no yeast. After two hours, only A has risen. A third bowl C has yeast but is kept in a refrigerator; it rises very little. Explain.

Step 1 — Only the bowls with yeast can ferment sugars, so the yeast causes the rise (A vs B).
Step 2 — Yeast releases CO₂ during fermentation; the gas is trapped in the dough, which puffs up.
Step 3 — Fermentation is an enzyme-driven process that slows down at low temperature, so C rises little.
Conclusion — a living microbe, working best at a suitable temperature, raises the dough.

Worked table: dough rises only with yeast and warmth
Bowl	Yeast	Temperature	Rise
A	Yes	Warm	Large
B	No	Warm	None
C	Yes	Cold	Very little

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