"Spoonful" has a one-chord, modal blues structure found in other songs Willie Dixon wrote for Howlin' Wolf, such as "Wang Dang Doodle" and "Back Door Man", and in Wolf's own "Smokestack Lightning". It uses eight-bar vocal sections with twelve-bar choruses and is performed at a medium blues tempo in the key of E. Music critic Bill Janovitz describes it as "brutal, powerful Wolf bellowing in his raspy style. There are few recordings that equal the powerful force of 'Spoonful,' or, for that matter, any other Wolf/Dixon Chess side."