Q.In which food would you find lactic acid bacteria? Mention some of their useful applications.

Let’s begin with something you already know. Think of a pot of milk left out in warm weather. After a few hours, it turns sour and thickens into curd. That change is not spoilage in the usual sense — it is a controlled transformation caused by tiny living organisms called microbes. This is the heart of microbial fermentation.

Fermentation is a process in which microorganisms — bacteria, yeast, or moulds — break down organic substances (like sugars) in the absence of oxygen, producing energy for themselves and, as a by‑product, substances that change the food. When we deliberately use this process to make food, we call the result microbial fermented foods.

You have eaten many of them without thinking twice: curd (yogurt), idli and dosa batter, bread, cheese, pickles, vinegar, and even the dark chocolate you might enjoy. Each of these relies on specific microbes doing their work.

Why does this matter? Because fermentation does three things that are valuable for us:

• Preserves food — The acids or alcohol produced by microbes prevent spoilage by harmful bacteria. Pickles stay edible for months because of lactic acid from fermentation.
• Improves digestibility — Microbes break down complex molecules. Lactose in milk becomes easier to digest in curd; the proteins in soy become more digestible in tempeh.
• Enhances flavour and texture — The tang of yogurt, the airy holes in bread, the umami of soy sauce — all come from fermentation.

Let’s look at a few examples from your daily life, as the NCERT would describe them:

• Curd (yogurt): Milk is boiled and cooled, then a small amount of previous curd (containing Lactobacillus bacteria) is added. The bacteria convert lactose into lactic acid, which thickens the milk and gives it a sour taste.
• Idli and dosa batter: Rice and urad dal are soaked, ground, and left to ferment overnight. Naturally occurring Leuconostoc and other bacteria produce carbon dioxide gas, which makes the batter rise and gives idlis their spongy texture.
• Bread: Baker’s yeast (Saccharomyces cerevisiae) ferments the sugars in dough, releasing carbon dioxide that makes the dough rise. The alcohol produced evaporates during baking.
• Cheese: Milk is curdled using rennet (an enzyme) or acid, then specific bacteria and moulds are added to ripen it. Different microbes give different cheeses their distinct flavours — for example, Penicillium roqueforti gives blue cheese its veins and sharp taste.

For a commerce or humanities student, the relevance goes beyond the kitchen. Fermented foods are a multi‑billion‑dollar industry. They involve supply chains (milk, grains, fruits), processing technology, quality control, and marketing. Understanding the basic science helps you see why a product like yogurt has a “use by” date, why some cheeses are expensive, and why traditional foods like kimchi or kombucha have become global trends.

In short: microbial fermentation is nature’s way of transforming food using invisible helpers. It is a bridge between biology and everyday life — and it has been feeding humanity long before anyone knew what a microbe was.

Microbial fermentation is a well-established topic in the NCERT Class 12 Biology curriculum, commonly explored through searches like "Microbial Fermentation Foods: definition, examples and applications" and "list microbes used in food production" ahead of CBSE board exams. Students preparing for NEET and other competitive exams often revise this alongside "Microbes in Human Welfare important questions," since it links directly to biotechnology and industrial microbiology.