The biggest brewer in southern Africa has launched the first commercial beer made from the cassava plant.Homebrew spirits on the continent, fermented from cassava and other root tubers, are popular because they are cheap but they can be lethal.SABMiller executives said the new beer would give consumers an affordable, safer alternative to such homebrews.Cassava is considered a staple food crop in Africa but the firm denies the beer will lead to food shortages.The beer, called Impala, is being brewed in Mozambique and will require about 40,000 tonnes of raw cassava per year.The BBC's Milton Nkosi in Johannesburg says when he tasted a chilled Impala it went down very well.It was somewhat bitter, somewhat tangy, not sweet - and it was not far off from some of the popular brands more expensive beer across the continent, he said Cassava accounts for 70% of the new brew.The SABMiller project - called Farming Better Futures - uses smallholder farmers to grow the cassava crop.Mark Bowman, the managing director of SABMiller, said to would offer enormous agricultural potential to farmers.It would create employment for more than 1,500 farmers and their families, the company said.Thanks to using locally grown cassava and a reduced tax rate agreed by the Mozambique government, Impala was 30% cheaper than mainstream lager, it said.