Discounter Aldi is now Australia's most profitable supermarket retailer and is set to reach 'tipping point', grabbing a bigger share of the main grocery shop and significantly disrupting the Coles and Woolworths duopoly.

According to a major report by UBS, Aldi's sales are expected to grow 15 per cent a year for the next three years – four or five times the rate of grocery market growth – reaching at least $10.6 billion and as much as $14.8 billion by 2019 if the discounter fixes perceived problems such as customer service and the quality of its fresh food.

UBS analyst Ben Gilbert expects Aldi's share of the national grocery market to rise from 7 per cent to at least 10 per cent by 2019-20, taking at least $1 billion in combined sales each year from Woolworths, Metcash and Coles.

While Aldi's prices are estimated to be 20 to 30 per cent cheaper than those at Coles and Woolworths, the discounter is now more profitable than the major chains. Earnings before interest and tax to sales are estimated to be around 6 per cent compared with 4.6 per cent at Coles and 5.4 per cent at Woolworths this year.