What is pasteurisation? Describe the methods of pasteurising milk.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Open in two lines. Pasteurisation is heating a food below 100 °C for a set time to kill all disease germs and most spoilage organisms, then cooling it quickly. Louis Pasteur developed it.
2 · Aim and index organism. Time and temperature are set to kill Coxiella burnetii, the most heat-resistant non-spore pathogen in milk; spores survive, so milk is kept cold.
3 · LTLT (holding) method. 63 °C for 30 minutes in a jacketed vat, then cooling.
4 · HTST (flash) method.
72 °C for 15 seconds in a plate heat exchanger.
Regeneration, heating, holding tube, flow-diversion valve, cooling to about 4 °C.
5 · Draw the HTST flow. [Flow: raw milk → regeneration → heating 72 °C → holding 15 s → regeneration → chilling 4 °C → packing]
6 · UHT and the phosphatase test.
UHT: 135-150 °C for a few seconds, then aseptic packing.
A negative phosphatase test shows adequate pasteurisation.
7 · Nutrition link. Protein, calcium and riboflavin are kept; vitamin C and thiamine losses are small. Institutions should use only pasteurised milk.
8 · Close in one line. Pasteurisation makes milk safe with little loss of quality, but the milk must be kept cold.
Scoring tip: Draw the HTST flow and give both temperature-time pairs; these carry most of the marks.
