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Food Science and Technology QUESTION #5907
Question 1
The purpose of the 'holding tube' in an HTST pasteurizer is:
  • It pre-heats milk before the heat exchanger; time \(= V/Q\) using fastest particle velocity
  • It maintains milk at \(\geq 72^{\circ}\text{C}\) for the required minimum time (\(\geq 15\) s); minimum length \(= 2 \bar{v} \times 15\;\text{s}\), using the fastest particle velocity as the worst case✔️
  • It holds milk at \(4^{\circ}\text{C}\) after cooling to prevent recontamination
  • It mixes raw and pasteurized milk for energy recovery
Correct Answer Explanation
The holding tube ensures EVERY particle receives the minimum heat treatment (\(72^{\circ}\text{C}\) for \(\geq 15\) s for HTST). The critical design parameter uses the FASTEST-moving particle (\(\approx 2\times\) mean velocity in turbulent flow) as the worst case: minimum length \(= 2\bar{v} \times 15\;\text{s}\).