Merge Batch

A merge batch operation takes two or more parent batches and combines their material into one child batch. The child gets a new batch ID and carries genealogy edges to every parent. Each parent contributes a known quantity, and the child inherits a quality profile that is a weighted combination of the parents — sometimes recalculated, sometimes requiring fresh testing.

• Parents — two or more complete batches, each with own quality profile and disposition.
• Merge event — defined operation (blending, pooling, charging into one vessel) with timestamps and equipment.
• Child — new batch with new ID, genealogy edges to every parent with quantity contributions.
• Quality recalculation — weighted assay, potency or other attributes based on parent profiles.
• Fresh testing where parents diverge — homogeneity, identity, microbial limits.

• Blending sub-lots — multiple granulation sub-lots blended into a final blend lot.
• Pooling harvests — multiple fermentation harvests pooled for downstream purification.
• Rework with fresh material — recovered material merged into a new production batch (with rework rationale captured).
• Buffer reuse — pooled buffer from multiple preparations consumed by one downstream process.
• Multi-source raw material — multiple supplier lots combined for a single production run.
• Tank top-up — running tank topped up from multiple incoming lots over time.

• Each parent batch ID and quantity contributed (with units).
• Child batch ID (newly issued atomically) and total post-merge quantity.
• Equipment used for the merge (blender, tank, vessel) for CIP and contamination context.
• Operator/signature per SOP — second-witness for regulated material.
• Time and order of contributions — sometimes critical (e.g. acid before base for chemistry safety).
• Quality attribute recalculation results (weighted assay, etc.) or test plan for fresh testing.

• Homogeneity — merged material may not be uniform; blend uniformity testing often required.
• Quality inheritance — child cannot be 'better' than worst parent on most attributes; weighted assay is the floor.
• Disposition coupling — if a parent is later found OOS, the merged child inherits the impact and may need recall.
• Hold-time aggregation — child's effective hold time is bounded by the oldest parent's exposure.
• Lot-size constraints — regulators expect declared lot sizes to be consistent with the merge pattern; ad-hoc merges may breach the registered scale.

ICH Q7 §14 explicitly addresses rework — material that has been processed once and is being reprocessed or merged into fresh production. Critical disciplines:

• Rework rationale documented and approved before the merge.
• Maximum rework percentage limits respected (typically 10–25%, product- and regulator-specific).
• Rework parent's history (why it failed first time, what was done to it) carried into child BMR.
• Fresh full release testing on the merged child — rework is not a release shortcut.
• Trending of rework frequency by product — process improvement signal, not normalisation target.

• Pharma — multiple granulation sub-lots merged into one final blend before compression.
• Biopharma — multiple bioreactor harvests pooled for downstream chromatography.
• Food — multiple ingredient lots combined into a single mix batch with traceability captured for FSMA 204.
• Cosmetics — multiple emulsion sub-batches pooled into a hold tank for filling.
• Chemicals — multiple reactor batches combined for distillation or final blending.
• API — multiple crystallisation sub-batches pooled and dried as one final API batch (with regulator-approved batch size).

• Merge captured only as quantity in/out — parent IDs lost.
• Tank top-ups not modelled as merges — running tank becomes 'unknown lot'.
• Weighted assay recalculation skipped — child released against the highest parent's results.
• Rework percentage limits unenforced — drift over time normalises poor process control.
• Homogeneity testing waived because 'we always blend well' — assumption not documented or validated.
• Order of merge not captured where safety-relevant — incidents under investigation cannot reconstruct sequence.
• Cross-site merges manually reconciled — genealogy edges drop at site boundaries.