What is the coffee bloom?

The coffee bloom is the fast release of carbon dioxide and other gasses as heated water comes in contact with the coffee grounds at the beginning of the brewing cycle. The grounds may bubble and appear to expand, creating a bloom. In a Moccamaster coffee brewer, the boiling action generated by the copper boiling element moves the water up the glass tube, where it flows into the outlet arm and pulses over the brew basket, blooming the coffee grounds in a manual pour-over style. You can witness this process by brewing with the brew basket lid off. However, to avoid burns and the excessive release of heat, we do not recommend doing so.