bottle

In web and sheetfed printing, to bottle means that printed pages rotate slightly relative to the fold line when a sheet is folded two or more times. The result is pages that sit askew within the finished booklet or saddle-stitched product, with the outer edges no longer aligned with the spine. This happens during the folding operation itself, not during printing.

The mechanical cause is straightforward: as the folding knife or roller presses the sheet, friction and the stiffness of the paper stock can cause the gripper edge (the edge held by the machine) to advance slightly faster or slower than the free edge. With each successive fold, these small rotations accumulate. A sheet folded twice, or a signature with four or more pages, shows the defect most visibly on the outer leaves. Paper moisture content, caliper, and finish all influence how readily a job will bottle.

When it matters and how to prevent it

Bottling becomes visible as soon as the book is opened: the edge of the outermost page sits noticeably short of or proud of its neighbors. In tightly trimmed products, a bottled edge may be cut away entirely. In loose-trimmed work, the misalignment simply looks sloppy. The defect is most troublesome in saddle-stitched magazines and newsletters where the outer cover pages wrap multiple signatures and any rotation compounds.

Prevention centers on the folding machine setup and material choice. Running paper at its target moisture content (usually 4.5 to 5.5 percent) reduces stiffness and grip inconsistency. Adjusting knife or roller pressure, feed timing, and the angle of the fold plate can minimize slippage. Some printers use slightly dampened blankets or apply edge treatment to the paper before folding. Very thick or coated stocks bottle more easily and may require slower speeds or softer fold rules.

The term likely derives from the shape of the misaligned edge, which can take on a slightly curved or bulging profile when pages rotate at different rates, vaguely resembling the silhouette of a bottle. It remains common in European and North American pressrooms, though the word appears less often in modern technical literature as fold quality monitoring has become more automated.