Quality Control, Sensory Evaluation, and Defect Troubleshooting
This domain tests how you prove a product meets specification and how you diagnose a defect back to a cause rather than guessing at a remedy.
Core rules
- Specification vs tolerance: a spec is the target; tolerances define acceptable range. Results outside tolerance trigger a decision - release, rework, hold or reject - recorded with justification.
- Routine QC: moisture, water activity, Brix/refractometer solids, pH, texture by penetrometer or texture analyser, colour in Lab*, fat and particle size, plus weight, seal integrity and metal detection.
- SPC: plot results over time; a run of consecutive points on one side of the mean, or points outside control limits, signals a process shift even when every result is in spec.
- Sensory methods: difference tests (triangle, duo-trio, paired comparison) answer is there a difference; hedonic scales answer how much is it liked. Never use a liking score to prove a difference.
- Panel discipline: controlled lighting and temperature, odour-free booths, coded random-order samples, water and plain crackers between samples, no smoking or strong flavours before testing.
- Defect mapping: graining (crystallisation), bloom (fat or sugar), cold flow, sticking and wrapper adhesion, cracking, mould, rancidity, off-flavour, burnt notes.
Worked example
Boiled sweets stick to their wrappers after three weeks. Spec is ≤2.0 % moisture; the retained sample reads 2.6–2.8 %, and invert sugar is 18 % against a limit of 12 %. Reasoning: excess moisture and excess invert both raise hygroscopicity, so the surface absorbs water and becomes tacky. Root cause is under-cooking plus over-acidification. Correct the cook endpoint and acid dose, re-test the retained samples, and extend the storage check to four weeks.
Traps
- Calling a defect 'bloom' without identifying fat or sugar.
- Treating an in-spec but trending result as no problem.
- Running a triangle test and reporting preference.
- Testing sensory samples in the production room where cocoa and caramel odours mask differences.