WHAT IS COFFEE BLOOM?
It’s very simple to make terrific coffee right at home that will rival that served at any good coffee joint (and by good, I don’t mean the ubiquitous little mermaid).
When coffee beans are roasted, CO2 gets trapped inside. From then on, the beans will slowly emit the gas over time — a process known as "DEGASSING" . When ground, the beans will emit gas more quickly, and when met with hot water, all of the remaining gas will escape rapidly. This is the bloom, and the more gas that’s escaping, the bigger the bloom will be.
All of this matters to you and your friendly coffee freaks for two reasons. One, “the majority of a coffee bean’s flavor compounds are trapped in the CO2 gases,” So, more gas = more flavor. Two, the amount of gas can indicate how fresh the beans are.