When dozens of people across the country got sick from eating contaminated romaine lettuce this spring, Walmart did what many grocers would do: It cleared every shred off its shelves, just to be safe.

Walmart says it now has a better system for pinpointing which batches of leafy green vegetables might be contaminated. After a two-year pilot project, the retailer announced on Monday that it would be using a blockchain, the type of database technology behind Bitcoin, to keep track of every bag of spinach and head of lettuce.

By this time next year, more than 100 farms that supply Walmart with leafy green vegetables will be required to input detailed information about their food into a blockchain database developed by I.B.M. for Walmart and several other retailers exploring similar moves.

The burgeoning blockchain industry has generated a great deal of buzz, investment and experimentation. Central banks are exploring whether it would be good for tracking money flows. Eastman Kodak has explored a blockchain platform that could help photographers manage their collections and record ownership of their work, while a group of reporters and investors are using the technology to start a series of news publications.

But essentially the only real-world uses have come from cryptocurrencies like Bitcoin, which use their own blockchains to store transactions. Walmart is now trying to bring blockchain into the lexicon of everyday consumers.

It is the first real instance of doing this at scale, said Brigid McDermott, vice president of I.B.M. Blockchain.

For Walmart, the initiative fits squarely into two key strategies: bolstering its digital savvy and emphasizing the quality of its fresh food to customers. The blockchain could also save Walmart money. When another food-borne illness hits like the E. coli outbreak affecting romaine the retailer would only have to discard the food that was actually at risk.

I.B.M. is trying to position itself as a leader in the emerging technology of blockchains. It is competing with established companies like Microsoft and upstarts like Ethereum, which have been developing projects in areas as varied as financial trading and music rights.

The Walmart effort will take time to roll out. In the meantime, it is likely to face questions from critics of the technology, who are skeptical of whether the blockchains being developed by corporations are all that different from old-fashioned online databases.

I cant see how doing this in a blockchain data format will make this magical in any way, said David Gerard, the author of Attack of the 50 Foot Blockchain.

I think its mostly a P.R. move, so these companies can sell themselves as blockchain leaders, he said.

Walmarts embrace of the blockchain highlights how difficult it still is for grocers, including the nations largest, to keep track of their food.

Last year, Walmart conducted an experiment trying to trace the source of sliced mangos.

It took seven days for Walmart employees to locate the farm in Mexico that grew the fruit. With the blockchain software developed by IBM, the mangos could be tracked in a matter of seconds, according to Walmart.

The food chain is not always linear, said Frank Yiannas, vice president for food safety at Walmart.

The original blockchain was the online database on which all Bitcoin addresses and transactions were stored. The database is maintained and stored by a network of volunteer computers, so that no single institution, like a bank, is required to keep the records. Because several computers have the records, it is much harder to change or fudge the data after the fact.

Many large global corporations have been studying how they might use a similar database design to keep records among a wide array of parties like the hundreds of people involved in moving spinach from the farm to the grocery shelf.

[Confused about blockchains? Heres what you need to know.]

The blockchains being tested by companies, including the version adopted by Walmart, generally have nothing to do with Bitcoin or any cryptocurrency they are entirely new databases with no coins involved. And unlike the Bitcoin blockchain, which can be viewed by anyone, only certain people will be able to view and access the Walmart database.

The system that Walmart is using, IBM Food Trust, has been developed for consumer companies, including Dole, Wegmans and Unilever, to track products moving through the supply chain.

At each stop along the way, people handling produce for Walmart will make an entry on the blockchain, signing off when they receive it and then when they move it onto the next person in the chain. IBM and Walmart say they are already tracking other products like yogurt and poultry on the system.

Blockchains are supposed to make it possible to keep updated databases without any central authority in charge. But currently, all of the records for the Walmart blockchain are being stored on IBMs cloud computers, for Walmarts use. That has led to questions about why a distributed database like a blockchain is even necessary.

The idea is right but the execution seems off, said Simon Taylor, the co-founder of 11:FS, a consulting firm that advises companies on blockchain adoption. IBM took new tech that doesnt need a middleman and made themselves the middleman.

Ms. McDermott said that the data would be encrypted in a way that will make it impossible for IBM to access or change it.

Efforts to track goods on blockchains have also faced a more fundamental challenge. A blockchain can capture the digital record of a box of spinach. But it cannot tell if someone opened the box and changed the spinach inside, replacing it with arugula or illegal drugs.

Blockchains wont protect you from fraud, Mr. Gerard said. You need human inspectors who know the scams.

Walmart says its blockchain will allow it to track food from the field, through washing and cutting facilities, to the warehouse and finally to the store. It will even be possible to pinpoint which part of the field and at what time the vegetables were harvested.

Mr. Yiannas said Walmart was focusing on leafy green vegetables because, along with beef, they tend to have the highest incidences of contagion.

We can bring trust to the system, he said.

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From Farm to Blockchain: Walmart Tracks Its Lettuce