Definition
A confectionery process in which a centre product (biscuit, wafer, marshmallow, nougat) is conveyed under a curtain of molten, tempered chocolate that completely coats the surface. After enrobing, the product is stabilised at 12–15°C in a cooling tunnel; the chocolate transitions to Form V cocoa butter crystals, gaining gloss and snap. Dew point control inside the tunnel is critical to prevent white/grey defects (fat bloom, sugar bloom).
Detailed Explanation
Enrobing is the most widely used coating technique in the chocolate sector. The line has three main zones: the enrober, the cooling tunnel, and storage/packaging. The centre product (biscuit, wafer, marshmallow, nougat, hazelnut bar) moves on a conveyor at 6–18 m/min; tempered chocolate (29–32°C) is poured over it as a curtain, fully coating the surface. Excess chocolate is removed by a draining belt and air knives below.
The "wet" coated product enters a 30–60 m cooling tunnel. The tunnel temperature profile is typically three-zone: • Zone 1 (inlet): 14–16°C, chocolate viscosity still low, forming begins • Zone 2 (middle): 8–12°C, Form V crystal growth peaks • Zone 3 (outlet): 14–18°C, product equilibrates with ambient and goes straight to packaging
Total tunnel time is 6–14 min; duration depends on chocolate thickness and centre-product heat capacity.
Desired output properties: glossy surface, snap (clean break), uniform shell thickness, 4–6 month shelf life. These targets are achievable only with correctly tempered chocolate + correct tunnel climate; if tunnel humidity control is neglected, sugar bloom and fat bloom defects appear.
Why It Matters
Enrobing quality is a consumer-visible attribute directly affecting brand value. With deficient tunnel climate control, four primary defects appear:
1. Sugar bloom — moisture condenses on the product surface, dissolves sugar crystals, and after drying leaves a whitish, non-glossy crystalline film. Irreversible — the product cannot be sold. 2. Fat bloom — cocoa butter migrates to the surface as grey patches or a full white film. Caused mainly by tempering errors + tunnel temperature shocks. 3. Matte finish — poor crystal structure (Form III/IV), gloss loss; no snap, soft texture. 4. Sticking — sticking to packaging, with shell delamination during shelf picking.
Financially these defects typically generate 3–10% waste; premium brands have a tolerance below 1%. By comparison: in a 5,000 t/year output, every 1% waste rise equals roughly 250,000–500,000 USD additional loss (at finished product cost).
Keeping tunnel ambient dew point below product surface temperature is not optional but mandatory; otherwise every droplet inside the tunnel becomes a potential sugar-bloom defect. For this reason, chocolate enrobing facilities operate with silica gel rotor dehumidifiers in a low-dew-point environment.
Practical Example
A Marmara chocolate plant produces 4,500 t/year of enrobed chocolate biscuits. Current issue: from May–September, sugar bloom rate is 4.2%; in winter, 1.1%.
Diagnosis: • Cooling tunnel ambient: 11°C / 70% RH (dew point 5.8°C) • Product surface temperature in Zone 2: 8°C • Critical finding: ambient dew point (5.8°C) appears below product surface (8°C), but tunnel door openings let outdoor air (summer 30°C/70% RH = dew point 24°C) cause short dew-point spikes; momentary condensation at product surface + sugar bloom
Solution: • TFT AD1000-3100 series silica gel rotor unit, AD2000 model • Process capacity: 2,000 m³/h • Outlet dew point: 0°Cdp • Additional vestibule at tunnel entrance (3 m length, air curtain) • Tunnel ambient redesigned: 11°C / 50% RH (dew point 1.2°C) • Vestibule: 16°C / 45% RH (dew point 4°C)
Six-month post-commissioning tracking: • Sugar bloom: 4.2% → 0.3% (summer) • Total waste: 2.8% → 0.5% • Additional annual revenue: 4,500 t × 2.3% × 8,500 USD/t ≈ 880,000 USD • Additional energy: 75 MWh/year (rotor reactivation); ROI 4 months
Engineering Note
Seven engineering criteria for enrobed chocolate line design:
• Warm-air infiltration — humid outdoor-air infiltration, which causes sugar bloom especially in summer, must be minimised at tunnel entries/exits via vestibules (door count, air curtain, stepped heating). • Dew-point setpoint — at least 3°C margin below product surface temperature; in practice tunnel ambient dew point sits between 0 and 3°Cdp. • Temperature-shock prevention — transitions between Zones 1, 2, 3 must be gradual; abrupt temperature change (>5°C/m) disrupts Form V crystal growth and increases fat-bloom risk. • Belt hygiene — chocolate residues and dust on the conveyor pose tunnel-hygiene and product-contamination risk; automatic belt brushing is recommended. • Airflow pattern — laminar (parallel-flow rather than cross-flow) is ideal for Form V crystal growth; turbulence causes uneven heat transfer at the surface. • Cooling capacity reserve — 20–30% reserve is needed for summer peak load; otherwise the temperature setpoint drifts on hot days. • Monitoring — ambient temperature + dew point measured at 4–6 points along the tunnel; product surface temperature measured by IR; data trended via SCADA.
In a properly designed system, total waste falls below 1%.
NKT Application Link
For this application NKT – Nem Kontrol Teknolojileri supplies TFT AD series silica gel rotor dehumidifiers and the TFT CD 160-980 condensation dehumidifier. It supports unit selection with capacity calculation and technology matching based on space conditions, target temperature and RH (or dew point) and moisture load, and provides technical service and spare parts. Design, installation and commissioning remain within the scope of the facility's designer and contractor.
