Practical Skills, Workshop/Laboratory Practice and Project Work
What the exam tests
This domain tests safe laboratory practice, standard analytical methods, sensory and record-keeping skills, and the ability to plan and report a small project. Expect questions on moisture, ash, fat, protein, acidity, total soluble solids, pH, weighing and duplicate sampling.
Core rules and concepts
- Weigh accurately on a calibrated balance, record tare and sample mass, and use duplicate samples where the method requires them.
- Moisture is usually determined by drying in a hot-air oven at 105 degrees Celsius to constant mass; ash by incineration in a muffle furnace at about 550 degrees Celsius.
- Fat is extracted with a solvent in a Soxhlet apparatus; protein is determined by Kjeldahl digestion, distillation and titration.
- Acidity is found by titration with standard alkali; total soluble solids by refractometer, corrected to 20 degrees Celsius; pH by a calibrated electrode.
- A project report should state the aim, materials, method, observations, calculations, results, discussion, conclusion and safety precautions.
Worked example
An empty moisture dish weighs 20.000 g. A 5.000 g sample is added, dried, cooled in a desiccator and reweighed. The dish plus dry sample weighs 24.200 g. Dry matter = 24.200 minus 20.000 = 4.200 g. Moisture = 5.000 minus 4.200 = 0.800 g. Moisture content = (0.800 divided by 5.000) x 100 = 16.0%. The result is reported on the sample as received, not on a dry basis unless stated.
Traps
Weighing a hot dish; skipping the desiccator; forgetting to subtract the dish tare; reporting one decimal place for a balance readable to 0.001 g; using an uncalibrated pH meter; failing to duplicate a critical measurement.