Bloom

The bloom is the initial phase of pour-over brewing where a small amount of hot water (typically 2-3x the coffee weight) is poured over the grounds and allowed to sit for 30-45 seconds. During this time, coffee releases carbon dioxide gas (CO2) that was trapped during roasting, causing the grounds to bubble and expand. This degassing is important because CO2 repels water, preventing even extraction. A good bloom shows active bubbling and expansion. If there's no bloom, the coffee may be stale. The bloom water should fully saturate the grounds without dripping through immediately. After the bloom, the remaining water is poured in stages. Some methods skip the bloom for very fresh coffee or use a longer bloom for very fresh, gassy coffee.