Perhaps it’s tempting, at this much remove from their late-‘60s heyday, to write Canned Heat off as simply a good-times, blues-boogie band of middle-class white kids co-opting black American musical forms and getting rich in the process. Fortunately, watching the two-hour documentary, The Canned Heat Story, does a great deal to put that conception to bed.

The story is narrated chiefly by the Heat’s longstanding drummer, Fito De La Parra, who comes across as a hugely genial, engaging and mischievous spirit, committed to setting the record straight with honesty, integrity and humour. Its hard not to develop a genuine affection for Fito as he spins out one anecdote after the other, direct to camera, with a directness and wisdom that seem to lend credence to everything he says. The story he tells is perhaps a predictable one, following an almost clichéd rock ‘n’ roll trajectory: the band forms in 1965, born of a genuine love and encyclopaedic knowledge of the blues on the part of its three founders, Henry Vestine, Bob Hite and Allan Wilson; a reputation for explosive live shows catapults the band into counter-cultural superstardom, culminating in an iconic performance at Woodstock; there are drug busts, record company rip-offs, hit singles; and then, of course, there’s the almost inevitable third act of death, disillusionment and dissolution.

What emerges most clearly is the genuine tragedy surrounding the lives of those three founder members. The band’s principle songwriter, Allan ‘Blind Owl’ Wilson – a an early advocate of radical environmentalism - succumbed to clinical depression and died of an overdose of barbiturates, a gesture seen by many as a deliberate bid to leave an uncaring and self-destructive planet behind. Vocalist, Bob ‘The Bear’ Hite, became tired and frustrated as the band’s popularity waned with the dominance of disco, finally overdosing on heroin in 1981 and, thus, missing by just a few years the band’s later resurrection as a much-loved institution. Of the three, though, it’s Henry ‘The Sunflower’ Vestine that cuts the most dramatic and enigmatic figure: a blisteringly talented electric guitarist with an almost pathological fascination for the underbelly of American life, drawn to the most damaging drugs, the most dangerous people and a catalogue of erratic behaviour that pretty much eclipsed his talent and left him something of a forgotten figure. Although he lived into the ‘90s, it’s impossible not to conclude that Vestine did as much as he could to derail his own career, revelling in the glorious extremes of his own personal imperatives.

But it’s not all sadness. Ultimately, we’re left with a feeling that Canned Heat were, above all, about joy and early concert footage drawn from a number of sources reminds us just how powerful their call to join in the boogie could be. There’s a spine-tingling early-evening performance from Woodstock; a still-fascinating studio mime-through of their classic outlaw-Beatnik anthem, ‘On the Road Again,’ and – best of all – an utterly mesmerising psych-blues stomp from the Rotterdam Pop Festival that reveals just how heavy they could be, as well as highlighting the much-overlooked improvised nature of their live work. Here, Bob Hite in particular comes across as a forceful presence, bringing structure to a sprawling jam by plucking perfectly formed vocal blues-tropes out of his memory and constructing an instant, spontaneous underground blues poetry.

With all that established, the additional disc – containing a performance from the 1973 Montreux Festival - is something of a disappointment, featuring what De La Parra calls the New Age line-up that convened after Wilson’s death. Sure, it’s fascinating to watch a speed-freak Vestine, hunched and skeletal, digging into his guitar, and vocalist-guitarist James Shane does a nice Ray Charles impression, but it’s clearly not the same band of blazing hippy-warriors that set the night on fire in their West Coast youth. Moreover, much of the set gets railroaded into pandering crowd-pleasing by a guest appearance from the blues original Clarence ‘Gatemouth’ Brown who commandeers the band for four tunes, wheeling out undeniably entertaining but somewhat self-conscious party tricks on guitar, vocals, violin and harmonica.

Do yourself a favour: if you want to really understand what made Canned Heat a truly great legend of the counter-culture, listen to what your uncle Fito has to say, sit back and dig those early performances. Even now, they’ve still got the power to blow you away.