What Limits Falling-Film Evaporator Throughput During Beet Sugar Campaigns?

Countercurrent beet cossette extraction discharges raw juice with dry substance typically between 14% and 16% w/w. The surface-active load in this stream is dominated by triterpene saponins, pectic fragments, and heat-coagulated protein, which together generate a stable foam phase in hot-juice receivers and evaporator feed tanks. When SILFOAM SD 860 is applied to sugar manufacture, the preferred injection point is the thin-juice line downstream of the last filtration step and upstream of the first evaporator effect. The concentrate is prediluted with clean condensate at ratios from 1:5 to 1:20 before metering with a diaphragm dosing pump. Initial field trials on beet thin juice commonly bracket addition between 5 mg/kg and 20 mg/kg thin juice, with final setting determined by differential pressure across the first effect and condensate chemical oxygen demand. Residual dimethylpolysiloxane in finished food must remain within the limit of 10 mg/kg stated in 21 CFR 173.340; sugar samples are typically withdrawn after crystallization and analyzed by inductively coupled plasma optical emission spectroscopy after solvent extraction.

In a seven-effect falling-film evaporator set with first-effect vapor above 110°C and last-effect vapor at 85°C to 95°C, foam carryover rapidly increases condensate COD and forces early cleaning cycles. The antifoam collapse mechanism at the vapor-liquid interface becomes less efficient if the dose is simply increased without compensating for residence time in the feed tank. Overdosing above approximately 25 mg/kg thin juice has been observed in production audits to deposit a hydrophobic film on calandria tube surfaces, lowering the overall heat transfer coefficient by reducing turbulent boundary-layer renewal. To avoid this, the dose is not continuously raised; instead the injection point is shifted to the recirculated hot-juice loop so that shear from the recirculation pump pre-disperses the emulsion. This application has a narrow processing window because thin-juice pH after first carbonatation is held at 10.5 to 11.0 and holds a high lime-specific surface area; an unstable pre-emulsion can adsorb onto calcium carbonate fines and lose antifoam activity. End products include white crystalline sugar and downstream molasses. Condensate COD below 100 mg/L is the main post-trial confirmation that foam carryover is controlled.

Beet storage time above 30 days increases pectic degradation products in raw juice, and the same evaporator set may require the upper end of the trial bracket. A cold-weather campaign with frost-damaged beets is more foam-stable; operators should not rely on a fixed dose from the previous campaign. The concentrate should be injected after the final filter press because calcium carbonate fines from second carbonatation can adsorb the active silicone and reduce efficiency. Filter cloth blinding with silicone-calcium soap agglomerates is an observed failure if the emulsion is injected before clarification. The evaporator differential pressure is logged at 5-minute intervals; a sustained increase of more than 15% over the clean-condition baseline triggers a CIP cycle and a review of antifoam dose. Condensate COD is measured by the dichromate method according to ISO 6060; values above 100 mg/L indicate sugar carryover and foam ingress into the vapor path.

During extended Aspergillus niger citric acid campaigns in 150 m³ stirred-tank reactors, the fermentation broth develops a tough foam phase because the fungus releases extracellular proteins, polysaccharides, and cell-wall fragments under submerged aeration. With airflow between 0.8 vvm and 1.0 vvm, backpressure at 1.5 bar, and temperature maintained at 30°C to 35°C, uncontrolled foam enters the headspace and contaminates air exhaust filters. SILFOAM SD 860 can be autoclaved as a prediluted 1:10 aqueous emulsion at 121°C for 20 min and then fed through a sterilizable peristaltic line directly into the reactor headspace or below the air sparger. The dose in fungal submerged fermentation must be determined against both foam height and dissolved oxygen because the silicone film that destabilizes foam lamellae also adds interfacial resistance to oxygen transfer. A starting dose of 10 mg/kg initial broth mass is generally evaluated and then adjusted upward in 5 mg/kg increments only when the foam probe records persistent cresting. The production bottleneck is not foaming alone but the trade-off between foam suppression and volumetric mass transfer coefficient; the process conflict is considered when silicone addition lowers kLa by more than 10% in bench-scale sulfite oxidation checks before campaign start. During the pH-stat phase at 2.0 to 2.5, the emulsion remains stable because the self-emulsifying system tolerates acidic broth better than many ester-based antifoams. End products include citric acid monohydrate, anhydrous citric acid, and trisodium citrate for beverage and pharmaceutical compounding. Residual silicone in the final crystal or salt must again be below 10 mg/kg in the relevant ready-to-use food; this is checked on the mother liquor and finished citrate powder before packaging.

In production-scale recovery, the broth is heated to 70°C to 80°C and treated with calcium hydroxide slurry, forming calcium citrate. Silicone antifoam that has not collapsed into the broth can associate with the gypsum by-product; this association is mechanically removed during filtration. A process conflict arises if the dose is pushed above 50 mg/kg because the calcium citrate filter cake becomes hydrophobic and filtration resistance increases. Plant personnel therefore record filter cake moisture and filtrate turbidity alongside foam height. The concentrate should not be premixed with strong mineral acids or with hypochlorite sanitizer because emulsion inversion and separation can occur in low-pH carrier streams. The preferred injection schedule in fed-batch citric acid cultivation is a small baseline after inoculum transfer followed by bolus additions triggered by foam contact probes, not a fixed 4-hour addition, because batch-to-batch variance in mycelial morphology changes foam stability and fixed interval additions can over- or under-damp the interface.

Molasses Slurry Gas Hold-Up in Fed-Batch Yeast Propagation

Fed-batch yeast propagation in molasses-based media typically reaches peak oxygen uptake after 8–12 h when molasses feed is split into incremental additions to suppress Crabtree metabolism. Cane and beet molasses contain suspended gums, calcium salts, organic acids, and soluble proteins that stabilize a viscous foam, especially at the high-gravity dilution used in commercial baker's yeast seed tanks where fermentable sugar pulses are kept below 120 g/L total sugar per feed pulse. The concentrated antifoam is dispersed 1:10 in pasteurized water and metered into the molasses dilution tank or directly into the seed fermenter at an addition bracket of 10–50 mg/kg diluted molasses feed. In 30 m³ to 50 m³ seed fermenters aerated at 0.8–1.5 vvm with pH held at 4.5–5.0, foam-out through the vent condenser is the main failure mode. The end products are compressed baker's yeast, cream yeast, and instant dry yeast; residual silicone in the yeast cream must comply with the same 10 mg/kg limit and is measured periodically on washed cream because silicone can concentrate with the yeast solids during centrifugation. The process limit in this sector is not heat stability but emulsion compatibility with molasses colloidal particles; if pre-dilution water hardness exceeds approximately 200 mg/L CaCO3 equivalent, the emulsion may partially salt out and should be prepared with demineralized water or clean condensate.

When a foam probe detects high headspace conductivity during a feed pulse, the usual corrective action is not to increase the antifoam continuously but to slow the molasses feed rate by 10–20% for 15–20 min while adding a small bolus. This preserves dissolved oxygen above 20% saturation and avoids the oversized feed pulse that creates a fermentative rather than respiratory carbon flux. The gas hold-up problem is aggravated when feeding ammonium phosphate with molasses because the resulting CO2 release under aerobic respiration increases the interfacial area. Plant audits on large seed fermenters record a lower foaming threshold in beet molasses than in cane molasses due to higher pectic content, which means the same addition rate is not transferable across substrates. A bench-scale bubble column test with 40°Bx molasses and air at 0.8 vvm is used to bracket dose before each campaign; published data for SILFOAM SD 860 in this exact viscosity range is limited, so this test provides the required production-scale setting.

When Potato Steam Peeling Raises Soluble Starch Concentration

When abrasive steam peeling raises soluble starch concentration in potato processing water, the rapid gelatinization of starch at 90°C to 100°C creates a thick, surfactant-stable foam in flumes, drum washers, and peel-scrubber recirculation tanks. The self-emulsifying concentrate is injected into the wash-water ring main at 5–20 mg/kg based on recirculated water flow, usually after the primary screen that removes peel fragments larger than 2 mm. The treated water then passes through hydrocyclones and a decanter centrifuge; without foam control, the hydrocyclone air core becomes unstable and starch separation efficiency drops. The main compliance consideration is that the final peeled potato or cut piece is washed with potable water after antifoam application, and any residual silicone in frozen french fry, chip, or flake production must remain below 10 mg/kg in the final food under 21 CFR 173.340. Because starch-laden wastewater is often concentrated by thermal evaporation before animal feed or biogas use, the antifoam dose must also be evaluated to ensure it does not coat evaporator heat exchange surfaces. A single addition point in the flume supply line is generally sufficient; the process is shallow because foaming is physically separated from the finished product by downstream peeling, washing, and blanching.

Spiral-wound whey ultrafiltration modules processing pasteurized sweet whey or acid whey are sensitive to air entrainment because even a small gas bubble film in the feed channel creates localized concentration polarization and reduces permeate flux. Sweet whey at pH 6.2–6.6 and temperature 40°C to 50°C contains β-lactoglobulin, α-lactalbumin, and phospholipids that stabilize foam in the balance tank and in the retentate recycle loop. The concentrate is prediluted with RO permeate to 1:20 and dosed into the feed balance tank at 5–20 mg/kg liquid whey before pasteurization at 72°C for 15 s. The monitored parameters are differential pressure across the 8-inch spiral-wound modules, normalized permeate flux at 2–4 bar transmembrane pressure, and gas bubbles observed in the retentate sight glass. Residual silicone in whey protein concentrate, whey protein isolate, or lactose powder must remain below 10 mg/kg; this is verified by inductively coupled plasma optical emission spectroscopy on the finished powder. The process conflict here is that overdosing or poor pre-emulsion can cause a hydrophobic layer on the membrane surface, which is not easily removed by standard alkaline detergent at pH 11.5, requiring an extended enzymatic cleaner cycle. Therefore the minimum effective dose is maintained, and the injection is placed after the raw whey pump but before the balance tank inlet to allow sufficient mixing. End products include whey protein concentrate 80%, permeate lactose, and demineralized whey fractions for infant and sports nutrition.

Invert Syrup Ion-Exchange Polishing Requires Destabilization of the Interfacial Film

After ion-exchange decolorization of invert syrup at 72–75°Bx and 60°C to 70°C, the clarified syrup may retain a low-density interfacial film composed of residual fatty acids, colloidal color bodies, and finely dispersed carbon fines. This film resists vacuum pan evaporation and causes bulk loading tank foam that reduces fill accuracy. The concentrate is sprayed into the syrup transfer line as a 1:100 dilution in glucose syrup, rather than water, to prevent localized viscosity reduction and to ensure prompt dispersion in high-osmotic-pressure syrup. A starting dose of 1–5 mg/kg syrup is evaluated in a sparged bench test at 60°C before plant-scale injection; published data for this specific configuration is limited, so the bench test rather than a fixed formula must determine the final addition. The main operational boundary is that downstream membrane or activated carbon polishing should not be exposed to high doses because the silicone film may blind the carbon column. End products include bottled invert syrup, confectionery glucose-fructose blends, and canned fruit packing syrup. The treated syrup then proceeds to vacuum pan boiling or bulk loading without a persistent interfacial film.