Falling rate period of Non-hygroscopic foods

FOOD TECHNOLOGY (25-09-2021)

Q1. Falling rate period of Non-hygroscopic foods?

  1. Single
  2. Double
  3. Multiple
  4. Zero

ANSWER: 1. Single

  • Explanation – When the food’s moisture content goes below the critical moisture content, the drying rate slows until it approaches zero at equilibrium moisture content. This is referred to as the “falling rate period.” Non-hygroscopic foods have only one period of falling rate, but hygroscopic foods have two. The plane of evaporation shifts inside the food water as it diffuses through dry solids to the drying air in the first stage.


Q2. In a _________, a material or mass of material contains so much water that liquid surface that exists will dry in a manner comparable to an open-faced body of water.

  1. Constant drying rate period
  2. First falling rate period
  3. Second falling rate period
  4. All of the above

ANSWER – 1. Constant drying rate period

  • Explanation: A material or mass of material containing so much water that a liquid surface exists will dry in a way similar to an open-faced body of water during a constant drying rate time. Diffusion of moisture from within the droplet maintains saturated surface conditions, and evaporation occurs at a steady rate as long as these circumstances persist. The constant rate of drying time will continue until free moisture develops on the surface, after which the moisture removal rate will gradually decrease.


Q3. The ratio of steam consumption to water evaporation in the drum dryer is from?

  1. 2.3 to 2.2.1
  2. 1.7 to 1.9.9
  3. 1.2 to 1.6:1
  4. 2.5 to 3.1.1

ANSWER: 3. 1.2 to 1.6:1

  • Explanation: The drum dryer is an indirect dryer that keeps the milk in a thin coating on a spinning steam-heated drum. For small volumes, drum drying takes up less area and is more cost-effective than spray drying. Steam usage to water evaporation ratios ranges from 1.2 to 1.6:1. The major disadvantages are that the product may have a scorched flavor, and solubility is much lower (85%) because of protein denaturation.


Q4. _________ dryer is most commonly used in the dairy industry.

  1. Single roller dryer
  2. Double drum atmospheric dryer
  3. Double roller dryer
  4. Spray dryer

ANSWER – B. Double drum atmospheric dryer

  • Explanation – In the dairy industry, the double drum atmospheric dryer is most commonly used. The liquid is pumped into a pool in the space above and between the two rolls from a trough or perforated pipe at around 70 degrees Celsius. Heat is delivered to the liquid, which is partially concentrated in the area between the rolls, through conduction. As the drum rotates, all of the liquid vaporizes, leaving a thin layer of dried product to be scraped off by doctor blades into the conveyor below.


Q5. _______  is a process by which the low-pressure vapor produced from the boiling milk in the calandria is recompressed to a higher pressure.

  1. Heat transfer surface
  2. Vapour recompression
  3. Ancillary effect
  4. Vapour separation

ANSWER: 2. Vapour recompression

  • Explanation: Vapour recompression is the process of recompressing the low-pressure vapor created by boiling milk in the calandria to greater pressure. This recompressed vapor is then employed to reheat the milk in the same or prior effect. As a result, the amount of steam used per kilogram of evaporated water is significantly reduced, cutting the condensed milk manufacturing cost.



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