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 , arranged to feed the web in a web feeding direction (A) from the inlet through the apparatus to the outlet , comprising at least one drive unit and at least one web direction device a number of print bars provided with print heads arranged to provide food graded ink on the first side of the web , wherein the at least one drive unit and at least one web direction device 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 and the second web turning arrangement provides a second slack downstream the number of print bars , characterised in that the apparatus further comprises a pre-treatment device arranged upstream the printer bars and downstream the first slack , and in that the at least one drive unit is arranged to feed the web in a reversed web feeding direction (A') of the web between the first and second slack 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 , arranged to feed the web in a web feeding direction (A) from the inlet through the apparatus to the outlet , comprising at least one drive unit and at least one web direction device a number of print bars provided with print heads arranged to provide food graded ink on the first side of the web , wherein the at least one drive unit and at least one web direction device 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 and the second web turning arrangement provides a second slack downstream the number of print bars , characterised in that the apparatus further comprises a pre-treatment device arranged upstream the printer bars and downstream the first slack , and in that the at least one drive unit is arranged to feed the web in a reversed web feeding direction (A') of the web between the first and second slack after an external downstream stop. <EOS>