Walmart is anxious about the safety of its food following bacterial outbreaks for lettuce and other food, and it's hoping technology will set shoppers' minds at ease. It's telling its leafy green suppliers to use a blockchain system (designed with IBM's help) to track the shipments of their produce. The secure, distributed ledger will help trace the vegetables' path from the farm to the store, revealing the source of any potential outbreak in seconds instead of days. This isn't just for Walmart's internal benefit, either. Eventually, you could scan a bag and use the blockchain to find out where your spinach came from.