“Hope sustains the farmer,” says the Latin proverb. So far this year, hopes of a bumper harvest have sustained investors worried about the inflationary impact of a rise in food prices. The fear is that the torrent of fiscal stimulus being sprayed round the global economy will result in too much cash chasing too few grains, and higher prices that stunt recovery, particularly in poorer countries.

Yet while a global shortage may have pushed sugar prices to their highest levels in three decades, prices of soyabeans and corn have languished thanks to near-perfect summer growing conditions across the US corn belt. The US Department of Agriculture last week forecast a record soyabean haul, a near-record corn crop and the lowest farm gate prices for both grains in three years.

At $9.56 a bushel, soyabeans are trading near the same level they hit during last year's market crash. This is in spite of thin stockpiles – the result of drought, which has devastated harvests in Argentina – and robust demand from protein-hungry China, where soyabean imports rose by a quarter in the nine months to June. Corn prices, meanwhile, have fallen 30 per cent in three months, even as demand for corn-based ethanol – which now accounts for a third of the US crop – is increasing, thanks to government mandates.