"We have a reasonable harvest from last season, of about 1.2 million tonnes, of which 400,000 tonnes will be the surplus available for the market," Biti told a news conference.
"The Grain Marketing Board expects to purchase an additional 50,000 tonnes. Very soon we will be issuing grain bills to finance the purchase. We are going to start with $5 million (bills) and the first issue will be by the end of this week."
Biti said Zimbabwe would also review a waiver of duty on grain imports, which was put in place to allow imports as the country grappled with acute food shortages.
"We are going to review the waiver…subject to considerations such as the availability of supplies from the local market and the need to build strategic grain reserves," he said.
"There are demands from millers who are saying we should restore duty because imports are killing them."
Zimbabwe has suffered severe grain shortages since 2000, which critics blame on President Robert Mugabe’s seizure of white-owned farms to resettle landless blacks.