The 1960s were the decade of soul. While the huge commercial success of Motown opened up white audiences previously inaccessible to black recording artists, soul extended far beyond Detroit. The distinctive Southern soul sound found its voice through Memphis’s Stax Records. In an era of segregation, Stax pioneered racial integration in post-Jim Crow Tennessee with bands such as Booker T and the MGs, and reached new heights by unearthing the formidable Otis Redding – not only a towering singer of genuine artistry, but a charismatic star who could steal the show at the 1967 Monterey Pop Festival and break through to the lucrative pop market.

By 1968, though, Stax’s fortunes had begun to suffer: an acrimonious split with their partners, Atlantic Records, had left them without the rights to most of their previous releases, and Redding’s tragic death in a plane crash robbed the label of its most marketable star.

Stax’s own turmoil was mirrored by the political upheavals around them. While soul music was able to find commercial success in white America, many black listeners were frustrated that this success was not reflected in the struggle for civil rights. As the journalist Stuart Cosgrove recounts in Memphis 68: The Tragedy of Southern Soul, tensions reached fever pitch in April 1968, when the assassination of Martin Luther King Jr. in Stax’s own city of Memphis triggered nationwide riots.

King’s death hardened the attitudes of many civil rights activists, and 1968 saw the rise of the Black Power movement: a defiant expression of black pride and identity that influenced a generation, and made worldwide headlines with Tommie Smith and John Carlos’s iconic salutes at the 1968 Summer Olympics. Black Power argued that, for all its commercial triumphs, soul had succeeded largely in enriching only the white record company owners; with only a few exceptions (such as the late Otis Redding), soul musicians themselves were often poorly recompensed for their work. Within the creative industries, demand was growing for black musicians to be given greater control – both financial and artistic – over their own creations.

Isaac Hayes knew financial hardship all too well. Born into sharecropping poverty, Hayes was to become the family breadwinner by the age of ten following his father’s death. Hayes juggled school and work throughout his teens and still found time to join the school band to gain access to instruments otherwise beyond his means. Miraculously, he worked his way up through the ranks at Stax, eventually finding success with songwriting partner David Porter. Together, Hayes and Porter penned some of Stax’s greatest releases, including Sam & Dave’s ‘Hold On, I’m Coming’ and the genre-defining ‘Soul Man’; as a solo artist, however, Hayes’s career foundered, with his 1968 debut Presenting Isaac Hayes a commercial flop.

Just as in the political world, the late sixties saw soul music arrive at a crossroads. The sugar-sweet sounds of the Supremes, Motown’s most successful act, may have continued to dominate the charts, but change was in the air. The genre was maturing, and a period of intense artistic creativity and innovation was beginning; even the Temptations, the biggest male soul group of the time, were experimenting with longer, more intricate arrangements and more socially conscious lyrics, reflecting the febrile political atmosphere. Short, radio-friendly ditties were giving way to darker, funkier grooves.

It was into this turbulent world that Hot Buttered Soul was born. Hayes was cautious ahead of releasing a second solo album, having been dismayed at the poor performance of his debut effort. Stax was in dire straits, however, and Hayes relented, with the proviso that he be given full creative control over every aspect of the album’s production. The result was the most ground-breaking and innovative soul album to date.

Totalling 45 minutes, the album consisted of only four tracks; even the shortest, at 5:10 minutes, was nearly twice as long as Hayes’s earlier hit ‘Soul Man’, and lengthy instrumental records would become a hallmark of Ike’s music for the rest of his career.

The opening notes of ‘Walk on By’, the album’s first track, must live in the pantheon of great musical intros; a soaring orchestral composition, the strings build to a monumental crescendo that transforms even the dreariest London commute into an Homeric epic. It’s over two minutes before Hayes’s husky bass opens up, swooping and diving around the chorus of backing singers; as the song progresses through wicked guitar riffs well past Dionne Warwick’s original’s 2:55 minutes, Hayes’s spurned lover descends steadily into madness over twelve minutes of increasingly agitated orchestration. Ditch the shortened five-minute single version; settle into a comfy chair and let the full Isaac Hayes experience wash over you.

Soon, a sweet tinkling piano refrain gives way to a guitar riff laden with attitude. ‘Hyperbolicsyllabicsesquedalymistic’, the album’s decadently verbose second track, is the only one penned from scratch by Hayes, and the song gives as good as its title suggests: “My gastronomical stupensity / Is really satisfied when you’re loving me”. Divining meaning from the lyrics here is a fun exercise for the restless of mind; whatever he’s talking about, with that bassline, it sure as hell ain’t divine.

‘One Woman’ – the baby of the album by some distance – is a step change from the previous tracks. Simple and understated amid its lengthier, self-indulgent siblings, ‘One Woman’ tells of a conflicted lover racked with romantic indecision. Hayes’s rendition demonstrates how love elevates the banal – a stolen meeting in a coffee shop, a weary rush-hour slog – into the profoundly human. A true gem, ‘One Woman’ is a forgotten masterpiece buried in a stellar album.

By the time they get to ‘By the Time I Get to Phoenix’, listeners have been fully acquainted with the Isaac Hayes approach to soul. Over an austere Hammond organ drone, Ike drops the singing altogether and boldly opens the track with an eight-minute spoken word soliloquy. Turning ‘One Woman’ on its head, Hayes spins a yarn of a faithful but fatally pliant protagonist, cursed with a deceitful lover. In ‘Phoenix’, we see the conflicting strands of Hayes’s world in 1969 dexterously woven together: echoes of soul’s religious roots in his ministerial monologue, but adapted for the profane rather than the profound; the Southern antebellum spectre of the other woman, but reimagined from a male perspective; seeking a better life out west, as many of Hayes’s contemporaries in soul were inspired to do by Sam Cooke, but wary of being left stranded far from home when the tides of fortune change; and all packaged in a 2:42 white country song, grooved up into 18 minutes of funk by a defiantly black Isaac Hayes. If not the easy-listening highlight of the album, ‘Phoenix’ is certainly the keystone to Hayes’s monument.

Hot Buttered Soul cleared a path for complex soul music in the emerging album market, laying the foundations for ambitious social critique in Marvin Gaye’s What’s Going On and Hayes’s own Oscar-winning film score for the Blaxploitation movie Shaft. In Hayes’s own words on ‘Phoenix’, “everybody got his own thing. I’m gonna bring it on down to Soulsville”. Thank God that you did, Ike.