An apparatus for digital printing of carton-based packaging material for packages holding liquid food products, wherein the packaging material has a first side adapted to form outer surfaces of the packages and a second side adapted to form inner surfaces of the packages, the apparatus comprising an inlet configured to receive a web of the packaging material and an outlet configured to transfer the web of packaging material out of the apparatus, a web feeding assembly (208a, 208b, 208c, 210, 211, 219, 224, 225), arranged to feed the web in a web feeding direction from the inlet through the apparatus to the outlet, comprising at least one drive unit (210, 211, 224, 225) and at least one web direction device (208a, 208b, 208c, 219) a number of print bars (216a, 216b, 216c, 216d) provided with print heads arranged to provide food graded ink on the first side of the web, wherein the at least one drive unit (210, 211, 224, 225) and at least one web direction device (208a, 208b, 208c, 219) provide a first web turning arrangement for turning the web after being received via the inlet such that the first side of the web is facing towards the print heads, and a second web turning arrangement for turning the web after the food graded ink has been provided by the print heads, wherein the first web turning arrangement provides a first slack upstream the number of print bars (216a, 216b, 216c, 216d) and the second web turning arrangement provides a second slack downstream the number of print bars (216a, 216b, 216c, 216d), characterised in that the apparatus further comprises a pre-treatment device arranged upstream the printer bars (216a, 216b, 216c, 216d) and downstream the first slack, and in that the at least one drive unit (210, 211, 224, 225) is arranged to feed the web in a reversed web feeding direction (A') of the web between the first and second slack (212, 226) after an external downstream stop. wherein the packaging material has a first side adapted to form outer surfaces of the packages and a second side adapted to form inner surfaces of the packages, the apparatus comprising an inlet configured to receive a web of the packaging material and an outlet configured to transfer the web of packaging material out of the apparatus, a web feeding assembly (208a, 208b, 208c, 210, 211, 219, 224, 225), arranged to feed the web in a web feeding direction from the inlet through the apparatus to the outlet, comprising at least one drive unit (210, 211, 224, 225) and at least one web direction device (208a, 208b, 208c, 219) a number of print bars (216a, 216b, 216c, 216d) provided with print heads arranged to provide food graded ink on the first side of the web, wherein the at least one drive unit (210, 211, 224, 225) and at least one web direction device (208a, 208b, 208c, 219) provide a first web turning arrangement for turning the web after being received via the inlet such that the first side of the web is facing towards the print heads, and a second web turning arrangement for turning the web after the food graded ink has been provided by the print heads, wherein the first web turning arrangement provides a first slack upstream the number of print bars (216a, 216b, 216c, 216d) and the second web turning arrangement provides a second slack downstream the number of print bars (216a, 216b, 216c, 216d), characterised in that the apparatus further comprises a pre-treatment device arranged upstream the printer bars (216a, 216b, 216c, 216d) and downstream the first slack, and in that the at least one drive unit (210, 211, 224, 225) is arranged to feed the web in a reversed web feeding direction (A') of the web between the first and second slack (212, 226) after an external downstream stop.