After an E.coli outbreak in romaine lettuce sickened more than 200 people in April, Walmart pushed suppliers to use IBM’s blockchain-based tracking software.

After an E.coli outbreak in romaine lettuce sickened more than 200 people in April, Walmart laid out a strict new policy to its suppliers of salad products.

“All fresh leafy greens suppliers are expected to be able to trace their products back to farm(s) (by production lot) in seconds – not days,” the company said in a letter last week.

To do this, Walmart introduced a new system for its suppliers that is fueled by a much-hyped technology — blockchain.

“Today, Walmart and Sam’s Club sent a letter to suppliers of fresh, leafy greens asking them to trace their products all the way back to the farm using blockchain technology,” Walmart said in a press release. “Suppliers are expected to have all these systems in place by this time next year.”