It is a procedure conducted in a 'tea ceremony for kuchikiri,' where the seal of a jar in which the first tea harvested in early summer is contained to let it stand is broken around the time of the first use of the fireplace.
初夏に採れた新茶を茶壺に封じて寝かせておき、炉開きの頃に封切る「口切の茶事」のための手続きである。