Every tea bag defect has a name, a cause and, on a well-run line, a checkpoint that is supposed to catch it before the bag reaches a carton. For a buyer sourcing private label tea or evaluating a new co-packer, it helps to work through the defect list itself: what goes wrong, and which inspection point is built to find it. None of the faults below are exotic — they are the ordinary failure modes of a string-and-tag bagging line.
Underfill and overfill: the grammage fault
The most common defect on any bagging line is a fill weight that drifts from the target gram weight. Underfill shorts the customer and risks a net-weight complaint, while overfill quietly erodes margin on every bag produced. Drift usually has a mechanical cause: a hopper running low, a blend settling and packing differently as it empties, or a fine-particle mix dosing less evenly than a coarse one. On an adjustable-fill line — TeraVella's runs roughly 1.5 to 3 grams depending on the tea, for example — the catch is a scheduled in-process weight check taken at intervals through the run, not only at start-up, so a drifting reading gets corrected while the batch is still on the machine.
Seal failure: when the filter paper doesn't close
A seal failure means the filter paper envelope of the bag itself has not closed properly, leaving a gap where fine leaf or herb particles can escape or where the infusion runs faster on one side than the other. Heat-seal temperature, dwell time and the condition of the sealing bars all affect this, and the fault can appear intermittently rather than on every bag in a run. The checkpoint is a visual and manual check at finished-bag inspection — pressing and examining a sample of sealed bags before cartoning — because a seal fault is far easier to catch before boxing than after a customer has opened the pack.
String tangle: a threading fault, not a mystery
String tangle happens when the thread connecting the bag to its paper tag twists, loops back on itself or catches on a neighbouring bag as it comes off the machine. It is a mechanical threading issue rather than a material defect, usually tied to spool tension or feed speed, and it tends to cluster in short runs rather than spread evenly across a batch. Because tangled strings are visible without any tool or test, they are caught at the same finished-bag inspection stage as seal faults.
The paper tag carries the brand name and, on a private label run, is often the single most visible branding element on the finished product. A torn tag usually points to a stock or tension issue at the tag-attach station, while a misaligned tag — printed side folded in, or set at an angle — points to feed alignment rather than print quality. Both faults are cosmetic rather than a food safety concern, but for a brand paying for custom tag printing, they matter commercially. Finished-bag inspection checks tag placement and legibility alongside the seal and string checks.
Envelope misalignment and closure gaps
Every bag TeraVella produces is wrapped in an individual outer envelope after bagging, and that step introduces its own failure mode: a fold that sits off-centre, a flap that has not closed fully, or print that runs crooked across the front. A poorly closed envelope defeats the reason for using one, since it no longer protects the bag's aroma and moisture between the line and the shelf. This is checked at the same finished-bag stage, immediately before the enveloped bags are counted into retail cartons — the last practical point to pull a faulty unit before it disappears into a sealed case.
HACCP principles behind defect prevention
Most of the defects above are quality and presentation issues rather than food safety hazards on their own, but the discipline behind catching them is the one HACCP principles ask for: identify where a control point sits, define an acceptable result, and check it at a set frequency rather than at random. TeraVella applies HACCP principles within its ISO 9001 and ISO 22000 system across its tea bag and dried fruit packing lines. That describes how the process is controlled, not a claim to hold a standalone HACCP certificate — a distinction worth keeping clear when reading any supplier's documentation.
What a buyer should ask about defect rates
A buyer does not need to walk a packing floor to judge how seriously a co-packer treats these checkpoints. Useful questions include how often fill weight is checked during a run, what finished-bag inspection covers, whether tangle and tag faults are logged separately from seal faults, and what happens when a defect rate crosses an internal threshold. A supplier that answers specifically, rather than with a general assurance, is describing a system that runs the same way whether or not a customer is watching. TeraVella quotes contract tea bag production, including private label runs, with these checkpoints built into the line and commercial terms confirmed at quotation.
