Food Process Engineering & Unit Operations

The engineering behind food factories. Learn material and energy balances, Brix and total solids, fluid flow and rheology of foods (Newtonian, shear-thinning, yield stress), pumping, heat exchangers and regeneration, evaporation and multiple-effect evaporators, membrane separation (RO, UF), mixing, size reduction, extrusion cooking, centrifugation, crystallisation, spray drying, CIP cleaning and hygienic design — with Python for evaporator mass balance, steam economy and pasteuriser heat duty.

Food processing plants combine standard unit operations — heating, cooling, separating, concentrating, mixing, forming, drying — tailored to delicate biological materials that must stay safe and tasty.

Engineers size equipment with mass and energy balances, and design it hygienically so it can be cleaned thoroughly.

An analogy

A food factory is like a kitchen scaled up a thousand times: instead of a pot you have heat exchangers, instead of a sieve a centrifuge, instead of simmering a sauce an evaporator — the physics is the same, but everything must be calculated.

Material and energy balances

What goes in must come out (plus accumulation). Solids balances size evaporators, dryers and blending; energy balances size heaters, coolers and boilers. Use a clear basis (per hour or per 100 kg), draw a block diagram, label known and unknown streams, then solve.

Heat transfer equipment

Choosing equipment:

Separation and forming

Centrifuges (cream separation, clarification), filtration and membranes (RO for concentration, UF for whey protein, MF for bacteria removal), extraction (oil, coffee), crystallisation (sugar, salt), size reduction (milling, homogenisation of milk), mixing and kneading, extrusion cooking (snacks, breakfast cereals, textured vegetable protein), spray drying (milk powder, instant coffee).

Rheology, hygiene and automation

Foods are often non-Newtonian: ketchup is shear-thinning with a yield stress, which affects pump selection and pressure drop. Hygienic design (EHEDG, 3-A): smooth stainless steel, no dead legs, self-draining, sanitary fittings. Clean-in-place (CIP) cycles use caustic, acid and sanitiser with controlled time, temperature, concentration and flow (Sinner's circle). Plants use PLC/SCADA, batch control (ISA-88) and energy integration.

Formulas

Worked example: Evaporator balance

Given: 5000 kg/h at 10 °Bx → 40 °Bx

Find: P and V.

Answer: 1250 kg/h concentrate, 3750 kg/h water

Worked example: Heat duty

Given: 2 kg/s juice, c_p 3.8, 20 → 90 °C

Find: Q.

Answer: 532 kW

Worked example: Regeneration efficiency

Given: Milk 4 °C in, regenerated to 65 °C, pasteurised at 72 °C

Find: RE.

Answer: 89.7%

Juice evaporator and milk pasteuriser

# Juice concentration: mass balance on an evaporator and steam economy
F, xF, xP = 10000.0, 0.12, 0.65          # kg/h feed, Brix fractions
P = F * xF / xP
V = F - P
print(f"concentrate {P:.0f} kg/h, water evaporated {V:.0f} kg/h")
for effects in (1, 2, 3):
    steam = V / (0.9 * effects)
    print(f"{effects}-effect evaporator: steam ~ {steam:.0f} kg/h (economy {V/steam:.2f})")
# Heat exchanger: milk heated 4 -> 72 C, 5000 L/h, cp 3.9 kJ/kgK, density 1.03
m = 5000 * 1.03 / 3600
Q = m * 3.9 * (72 - 4)
print(f"heat duty {Q:.0f} kW; with 90% regeneration only {Q*0.1:.0f} kW new heat")
# concentrate 1846 kg/h, water evaporated 8154 kg/h
# 1-effect evaporator: steam ~ 9060 kg/h (economy 0.90)
# 2-effect evaporator: steam ~ 4530 kg/h (economy 1.80)
# 3-effect evaporator: steam ~ 3020 kg/h (economy 2.70)
# heat duty 379 kW; with 90% regeneration only 38 kW new heat

Concentrating juice from 12 to 65 °Brix removes 82% of the feed mass as water. Each additional effect reuses vapour as the heating medium, cutting steam roughly in proportion (plus MVR/TVR can do even better). A plate pasteuriser's regeneration section uses hot pasteurised milk to preheat cold incoming milk, saving 90% of the heating energy.

Common mistakes

Applications

Key takeaways

Going further