Microorganisms play a vital role in fermentation by breaking down complex compounds into simpler products. The most common microorganisms involved are bacteria, yeasts, and molds. Lactobacillus species are widely used in dairy and vegetable fermentation to produce lactic acid. Saccharomyces cerevisiae, a type of yeast, is essential for alcoholic fermentation in bread, beer, and wine production. Acetic acid bacteria help convert alcohol into vinegar. Molds like Aspergillus are used in fermenting soy products like miso and soy sauce. Each microorganism contributes unique enzymes that affect texture, flavor, and preservation. Their controlled use ensures consistency and safety in fermented foods.