Monosaccharides are the simplest carbohydrates: single sugar units such as glucose, fructose, and galactose that cannot be broken down further by hydrolysis. They are the building blocks of disaccharides, oligosaccharides, and starches, and they are directly fermentable by yeast and bacteria, which makes them the immediate fuel of brewing, winemaking, and bread doughs. In foods they provide sweetness, participate in Maillard browning and caramelization, contribute to osmotic preservation in jams and honeys, and serve as rapid energy sources. Analysts measure them by HPLC and enzymatic methods to characterize honey, fruit juices, and fermentation progress.