Buying practices of the world's biggest coffee companies have come under renewed public scrutiny from a new film which explores the journey of coffee beans from plantation to cup.

The film, called Black Gold, vividly depicts the poverty and uncertainty in the lives of Ethiopian coffee producers, and calls for more commitment to a sustainable coffee supply chain.

Dubbed by some as the next ‘Supersize Me', Black Gold will launch in the UK at a time when ethical food and drink sales in the country have hit record highs, posing a challenge for producers and retailers.

Tadesse Meskala, head of the Ethiopian Oromia coffee co-operative, takes centre stage in the film as he is shown attempting to get a better price for his 74,000 producers. “Our hope is that one day the consumer will understand what he is drinking,” Meskala says.

In one scene, his farmers are amazed and others almost amused to discover just how much their coffee sells for in developed world coffeehouses and cafes. Producers on average get less than $0.3 for a $3 cup of coffee.

Coffee prices hit a 30-year low between 2001 and 2003, giving producers in developing countries a torrid time. Ethiopia depends on coffee for roughly 67 per cent of its export revenue. Prices have begun to recover in the last year, leading to hopes that some kind of stability can be found in the supply chain.

Proposals for a new International Coffee Agreement, intended to improve market stability, were discussed by the International Coffee Council last month. The world's four largest coffee firms, Nestlé, Kraft, Procter & Gamble and Sara Lee, declined an offer to participate in Black Gold. A spokesperson for Nestlé said the firm would prefer to see the film before commenting fully.