Write a note on preservation by concentration and evaporation.

1. 1 · Open in two lines. Concentration removes part of the water from liquid foods; it cuts bulk and, with other hurdles, helps preservation.
2. 2 · Aims. Less weight and volume, a step before drying, new products, lower water activity.
3. 3 · Methods.
   • Open-pan evaporation: khoa, jaggery.
   • Vacuum and multiple-effect evaporation: tomato paste, condensed milk.
   • Freeze concentration and membrane methods (RO, UF): juices, whey.
4. 4 · Draw a vacuum evaporator. [Sketch: steam-heated vessel → vapour to condenser → vacuum pump; concentrate drawn off at the bottom]
5. 5 · Products and combined hurdles. Sweetened condensed milk (sugar), evaporated milk (canned), frozen juice concentrate (freezing).
6. 6 · Nutrition link. Vacuum and membrane methods keep more vitamin C and colour than open boiling.
7. 7 · Close in one line. Concentration saves space and cost, and preserves best when combined with sugar, heat or cold.

Scoring tip: Name one product for each method; examiners look for khoa, tomato paste and condensed milk.