In the beginning of the 1990s, the whole aforementioned group had moved to Helsinki and started training at the Sibelius Academy. Sari started singing with the other girls, and the background line-up stabilized as consisting of Janne Lappalainen, Tommi Viksten, Tom Nyman, Riitta Potinoja, and Kari Reiman. Värttinä made a demo record which led to a recording contract with Sonet Records. The single "Marilaulu", released in the autumn, increased the public interest even more, and the album "Oi Dai", released in the spring of 1991, became the band's breakthrough. They had now formed their style, which consisted of strong and energetic female singing, music pieces based on the Finno-Ugric music tradition, and a band playing acoustic instruments. The style they created, mixing folk music into rock, jazz and popular music, was unheard of before.