A method, performed by a network data processing system, for tracking food data transactions in the network data processing system, wherein • the network data processing system is connectable to a hardware data processor of a food packaging machine, ∘ the food packaging machine comprising ▪ a packaging material supply module, ▪ a food supply module, ▪ a filling module; ∘ the filling module being operable to ▪ form a package from packaging material supplied by the packaging material supply module, ▪ fill food supplied by the food supply module into the package, ▪ seal the filled package, ▪ output the sealed, formed, and filled package; • the network data processing system being connectable to a plurality of separate network storage devices (161, 162); the method being characterized in that the steps of the network data processing system comprise: • reading from one of the network storage devices a packaged food production data hash tree, • receiving a food data transaction from the hardware data processor, the food data transaction being derived from data comprising ∘ a time stamp indicative of the time at which the filling module filled the supplied food into the formed package and then sealed the package, ∘ a machine data record identifying the filing module or the food packaging machine, ∘ all or part of a packaging material data record indicative of the packaging material batch using which the formed package is formed, ∘ all or part of a food data record indicative of the food batch filled into the formed package; • appending the food data transaction to the packaged food production data hash tree and • causing decentralised storage of identical instances of the appended packaged food production data hash tree in the plurality of network storage devices. • the network data processing system is connectable to a hardware data processor of a food packaging machine, ∘ the food packaging machine comprising ▪ a packaging material supply module, ▪ a food supply module, ▪ a filling module; ∘ the filling module being operable to ▪ form a package from packaging material supplied by the packaging material supply module, ▪ fill food supplied by the food supply module into the package, ▪ seal the filled package, ▪ output the sealed, formed, and filled package; ∘ the food packaging machine comprising ▪ a packaging material supply module, ▪ a food supply module, ▪ a filling module; ▪ a packaging material supply module, ▪ a food supply module, ▪ a filling module; ∘ the filling module being operable to ▪ form a package from packaging material supplied by the packaging material supply module, ▪ fill food supplied by the food supply module into the package, ▪ seal the filled package, ▪ output the sealed, formed, and filled package; ▪ form a package from packaging material supplied by the packaging material supply module, ▪ fill food supplied by the food supply module into the package, ▪ seal the filled package, ▪ output the sealed, formed, and filled package; • the network data processing system being connectable to a plurality of separate network storage devices (161, 162); the method being characterized in that the steps of the network data processing system comprise: • reading from one of the network storage devices a packaged food production data hash tree, • receiving a food data transaction from the hardware data processor, the food data transaction being derived from data comprising ∘ a time stamp indicative of the time at which the filling module filled the supplied food into the formed package and then sealed the package, ∘ a machine data record identifying the filing module or the food packaging machine, ∘ all or part of a packaging material data record indicative of the packaging material batch using which the formed package is formed, ∘ all or part of a food data record indicative of the food batch filled into the formed package; • appending the food data transaction to the packaged food production data hash tree and • causing decentralised storage of identical instances of the appended packaged food production data hash tree in the plurality of network storage devices. • reading from one of the network storage devices a packaged food production data hash tree, • receiving a food data transaction from the hardware data processor, the food data transaction being derived from data comprising ∘ a time stamp indicative of the time at which the filling module filled the supplied food into the formed package and then sealed the package, ∘ a machine data record identifying the filing module or the food packaging machine, ∘ all or part of a packaging material data record indicative of the packaging material batch using which the formed package is formed, ∘ all or part of a food data record indicative of the food batch filled into the formed package; ∘ a time stamp indicative of the time at which the filling module filled the supplied food into the formed package and then sealed the package, ∘ a machine data record identifying the filing module or the food packaging machine, ∘ all or part of a packaging material data record indicative of the packaging material batch using which the formed package is formed, ∘ all or part of a food data record indicative of the food batch filled into the formed package; • appending the food data transaction to the packaged food production data hash tree and • causing decentralised storage of identical instances of the appended packaged food production data hash tree in the plurality of network storage devices.