Champagne's bubbles are fermentation's CO₂ — Dom Pérignon's monks learned to trap it. Idli-dosa batter rises because Leuconostoc bacteria and yeasts ferment overnight — Indian kitchens run bioreactors daily. Bioethanol (E20 petrol in India) is yeast fermenting sugarcane molasses — fuel from fermentation. But the same process spoils: sour milk, rotting fruit — fermentation uncontrolled.