Describe spray drying and drum drying with their merits and demerits.

1. 1 · Open in two lines. Spray and drum dryers turn liquid and semi-liquid foods into powders or flakes.
2. 2 · Spray drying.
   • Liquid, often pre-concentrated, is atomised into a hot-air chamber.
   • Droplets dry in seconds; evaporation keeps them cool.
   • Powder falls out; fines are caught in a cyclone.
3. 3 · Draw a spray dryer. [Diagram: feed pump → atomiser → drying chamber with hot-air inlet → powder outlet → cyclone → exhaust]
4. 4 · Drum drying.
   • Thin film on a steam-heated rotating drum (single, double or vacuum).
   • Dries in one turn; a doctor blade scrapes it off as flakes.
5. 5 · Draw a double-drum dryer. [Diagram: two steam-heated drums turning inwards, feed between them, blades scraping off flakes]
6. 6 · Compare and give merits and demerits.
   • Spray: fine, soluble powder, little heat damage; costly, liquids only.
   • Drum: cheap, handles pastes; heat damage, poorer solubility.
7. 7 · Nutrition link. Milk powder and infant formula (spray) and weaning cereal flakes (drum) supply protein and calcium where fresh milk is scarce.
8. 8 · Close in one line. Spray drying gives better quality; drum drying is simpler and cheaper.

Scoring tip: Two neat labelled diagrams and a comparison table cover most of the marks.