Sanyo Electric has delayed the introduction of an optical disc based on a polymer derived from corn.

The disc, dubbed "MildDisc" by Sanyo, was to have been offered to customers from December last year and volume production was due to begin in the first half of this year but this has been delayed while Sanyo refines the technology, says Ryan Watson, a spokesperson for the Osaka-based company.

"There was a concern that if the disc was exposed to heat greater than 50 degrees Celsius that it wouldn't work properly," says Watson. "A timely topic now as the heat is blazing down on Tokyo, so the main obstacle that they are working on now is trying to improve the disc's resistance to heat. They could easily improve its resistance to heat with a mix of material but that kind of defeats the purpose of the MildDisc."

Sanyo has no current estimate on when it will be introduced.

Production of the plastic used in the MildDisc begins with Cargill Dow in the US, which mills kernels of corn to separate out the starch and then processes these to get unrefined dextrose. Using a fermentation process similar to that of beer production, the dextrose is converted into lactic acid, according to the company's website.

Sanyo converts the lactic acid into a polymer used in the disc substrate using a method developed with Japan's Mitsui Chemicals.

Sanyo estimates that around 85 corn kernels, each weighing an average of 0.5 grams, are needed to produce enough polymer for a single 4.7-inch optical disc, so an average ear of corn can produce around 10 discs.

The International Recording Media Association estimates world demand for CDs at around 9bn annually, and the US Department of Agriculture estimates world corn production at about 600m tons, so less than 0.1 percent of the world's corn production is theoretically required to produce enough polymer to satisfy worldwide disc demand.