FOOD90007 Chap.5 Concentration and Moisture Removal

Concentration and Moisture Removal

Evaporation partially removes water from liquid food by boiling. Lower pressure reduces boiling temperature, which can limit heat damage and enable vapour from one effect to heat another at a lower pressure. Distribution, heat-transfer area, separator performance, viscosity and fouling determine capacity and product exposure.

Preheating, multiple effects and vapour recompression can reduce fresh-steam demand, but longer residence or poor circulation can increase deposits and thermal change. Concentration also raises viscosity and boiling-point elevation, altering transfer as the run proceeds. A juice concentrator saves steam after adding another effect but the final effect receives a more viscous product and loses circulation.

Nominal economy improves while residence time and flavour damage rise unless the system is rebalanced. Record pressure gradient, feed distribution, concentration, residence time and condensate path. Compare economy on the same water removal duty and verify that entrained droplets are separated from vapour. Technology selection for evaporation requires equivalent targets.

Compare two operations at the same safety or preservation outcome, then examine how their transfer mechanism changes vacuum. Equipment cost, water, energy, cleaning, capacity and product loss belong beside sensory quality. The case for steam economy remains conditional until the coldest, slowest or least-exposed relevant region has been validated under realistic loading and storage.

Trace the most credible failure involving evaporation backwards from the finished food. Ask whether vacuum arose during preparation, transfer, holding, packaging or storage. Early in drying, a wet surface may support a near-constant evaporation rate when internal water replenishes it. As surface regions dry, moisture movement from the interior becomes limiting and the rate falls.

Equilibrium moisture depends on air condition; free moisture is removable under that condition, while bound water is held more strongly. High temperature and dry fast air increase the external driving force, but if evaporation outruns internal movement the surface can harden and restrict later transfer. Composition, fibre direction, piece size, humidity and air velocity therefore influence both duration and quality.

Fruit pieces develop a dry shell while their centres remain wet. Increasing heater output intensifies the gradient but does not repair the internal diffusion limit. Smaller geometry or a staged humidity-temperature profile may produce a more uniform endpoint. Plot rate against moisture content and identify the transition between control regimes.

Specify final moisture in relation to storage humidity and quality; a low average can conceal dangerous wet regions. Draw drying rate as incoming material, transformation zone and outgoing state. Attach a measurable limit to each arrow and locate the sample or sensor supporting bound moisture. Averages can conceal particles, packages or surface regions that receive a different history.

When case hardening approaches its boundary, describe the failure mode and corrective action rather than merely recommending a more intense process. For scale-up of drying rate, separate intensive variables from throughput, area and residence effects.

What this chapter covers

• 01

  Evaporation removes solvent under a controlled boiling condition

• 02

  Drying shifts from surface control to internal moisture movement

Worked application: Evaporation removes solvent under a controlled boiling condition

Key terms

Controlled-boiling evaporation

Evaporation removes solvent under a controlled boiling condition — Evaporation partially removes water from liquid food by boiling. Lower pressure reduces boiling temperature, which can limit heat damage and enable vapour from one effect to heat another at a lower pressure. Distribution, heat-transfer area, separator performance, viscosity and fouling determine capacity and product exposure. Record pressure gradient, feed distribution, concentration, residence time and condensate path. Compare economy on the same water removal duty and verify that entrained droplets are separated from vapour.

Drying-rate control regimes

Drying shifts from surface control to internal moisture movement — Early in drying, a wet surface may support a near-constant evaporation rate when internal water replenishes it. As surface regions dry, moisture movement from the interior becomes limiting and the rate falls. Equilibrium moisture depends on air condition; free moisture is removable under that condition, while bound water is held more strongly. Plot rate against moisture content and identify the transition between control regimes. Specify final moisture in relation to storage humidity and quality; a low average can conceal dangerous wet regions.

Concentration and Moisture Removal FAQ

Exam move

Open a process ledger for Concentration and Moisture Removal. Record food state, target, driving force, equipment path, limiting region and quality consequence. Begin with evaporation and reconstruct the causal or institutional route without copying the worked response. Change one feature of the case and decide whether vacuum still supports the same interpretation.

Write a credible rival account and identify the observation that would discriminate between them. Return to case hardening and state the boundary it places on transfer to another setting. Check that each recommendation names a decision, responsible actor and observable consequence. Use the chapter questions for retrieval, then consult the detailed prose only to correct the mechanism or evidence limit.

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