ポン菓子

High pressure puffed grain is created by placing whole grains under high pressure with steam. When the containment vessel's seal is suddenly broken, the entrained steam then flashes and bloats the endosperm of the kernel, increasing its volume to many times its original size.
Puffed rice or other grains are occasionally found as street food in Japan (called "pong gashi"), where peddlers implement the puffing process using an integrated pushcart/puffer featuring a rotating steel pressure chamber heated over an open flame. The great booming sound produced by the release of pressure serves as advertising to attract customers.