Practical skills, laboratory work and project assessment
What this domain tests
This domain assesses practical laboratory technique and project work: sampling, titration, Gerber fat, moisture/ash, sensory evaluation, record-keeping and interpretation. Marks are lost for poor technique and missing units, not only wrong answers.
Core rules
- Use clean, calibrated glassware; label samples and record temperature and time.
- For acidity, titrate a measured milk sample with standard NaOH using phenolphthalein to a persistent pink endpoint.
- Gerber fat uses sulfuric acid to digest protein and release fat, which is read in a butyrometer; follow safety precautions.
- Moisture is measured by oven drying, ash by muffle furnace, protein commonly by Kjeldahl.
- Sensory tests need coded samples, trained panellists, controlled lighting and no discussion.
- Project reports need aim, method, controls, raw data, calculations and conclusions.
Worked example
Titrate 10.0 mL milk with 0.1 N NaOH; the burette reading is 1.8 mL. % lactic acid = (V × N × 0.09 × 100)/sample volume = (1.8 × 0.1 × 0.09 × 100)/10 = 0.162%. The reasoning is that 1 mL of 1 N NaOH is equivalent to 0.09 g lactic acid; the N and sample volume scale it.
Traps
Read the bottom of the meniscus and use a white tile. Do not overrun the endpoint; a faint pink that persists is the end point. Never pipette by mouth. For Gerber, acid burns are serious; add acid carefully and use the centrifuge correctly. Record units and repeat titrations.