Songs of the summer should be crowned not in the giddiness of July but in the waning days of September, once the hot season has finished its business. A rearview perspective suggests that “Toast,” by the nineteen-year-old “singjay” Koffee, and produced by Walshy Fire, of Major Lazer, and IzyBeats, ruled this season. It was a mellow, cheery reign. At parties, I would watch eyebrows slacken and shoulders relax as the opening notes bounced into the room. “We haffi give thanks like we really supposed to,” Koffee advises nimbly; the song, about choosing optimism and practicing gratitude, is itself something to be thankful for. “Toasting” also refers to a kind of vocal work—not quite singing, more like charismatic chanting over a beat, or “riddim”—that is deeply associated with mid-century Jamaican music. Koffee was born Mikayla Simpson and was raised in Spanish Town, outside of Kingston, Jamaica. She sang in the church choir, played guitar, and won a school talent show that she’d entered somewhat unwittingly. In 2017, an acoustic-guitar performance of a song called “Legend,” which she had written in honor of the Jamaican sprinter Usain Bolt, went viral after Bolt reposted the video on Instagram. Alongside artists like Protoje and Chronixx, Koffee has emerged as a modernizer of the roots-reggae philosophy practiced by artists such as Beres Hammond, Peter Tosh, and Bob Marley. On her EP “Rapture,” her sound seamlessly blends reggae and dancehall, socially conscious messaging and free-spirit liveliness. On the track “Raggamuffin,” with liquid agility, she offers a critique of the Jamaican government. On “Throne,” she praises her own song-writing prowess: “Lyrics put your very welfare / Pon the death row, pon the wet floor.” “Toast” was an explosive début single. Earlier this year, Koffee won a prize for single of the year at the Jamaica Music Industry Association’s annual awards ceremony and performed on “Jimmy Kimmel Live!”; it’s been rumored that she was courted by Rihanna to write on her upcoming reggae album. To understand both the history and the future of Jamaican music, listen to Koffee.