In denim garment processing, acidic cellulase is applied as a pumice-free abrasion agent in rotary drum machines with load capacities commonly between 100 and 600 kg. The treatment is typically carried out after desizing, because residual sizing film from warp yarns blocks the access of cellulase to cotton cellulose. A standard desizing step uses bacterial α-amylase at 60–70°C and pH 6.0–6.5 for 10–15 min, followed by a drain and rinse before the cellulase bath is prepared. The cellulase bath is set at pH 4.5–5.0 with acetic acid and sodium acetate buffer at 1.0–2.0 g/L, and the garment load is processed at a temperature setpoint of 45–50°C. The enzyme dose is not fixed across product supply; it must be normalised against endoglucanase activity on carboxymethyl cellulose or against the supplier's own activity unit. Commercial acidic cellulase formulations derived from Trichoderma longibrachiatum are endoglucanase-rich and are selected because endoglucanase action on amorphous cotton cellulose weakens the outermost yarn layer without the deep cellulose scission produced by cellobiohydrolase-rich cocktails. In full-scale production, a dose of 0.5–1.5% owf of a standard 10,000 U/g-grade liquid is common, but batch-to-batch variation in denim cover factor, yarn twist and dye penetration shifts the required contact time between 20 and 45 min. Mechanical action at 25–35 rpm in a drum tumbler is required; without sufficient mechanical shear, indigo is removed unevenly and the garment surface shows streaking.

The main process risk is backstaining, where indigo particles removed from warp yarns redeposit onto white weft, pockets or embroidery. Backstaining is minimised by keeping the bath below pH 5.0, adding a nonionic detergent or polyvinylpyrrolidone anti-redeposition agent at 0.2–0.5 g/L, and avoiding a temperature higher than 55°C, which increases dye particle mobility. A secondary risk is tensile strength loss, because cellulase continues to hydrolyse cellulose if the enzyme is not inactivated after the desired level of abrasion. Dump the bath and raise the pH to 9.0–10.0 with sodium carbonate or raise the temperature above 80°C for 10 min to denature the enzyme; incomplete inactivation leads to residual attack during subsequent rinsing, drying and finishing. Tensile strength retention is measured in warp and weft directions according to ISO 13934-1:2013 or ASTM D5034-21. In typical production batches, the warp strip tensile loss is 8–15%, and acceptance is set by the garment specification rather than by a universal limit. A garment that loses more than 18% of its original warp tensile strength shows seam failure in high-stress areas and is usually rejected.

Substrate variation affects dose-response more than the nominal enzyme activity. Heavyweight denim above 14 oz/yd² requires longer treatment or a higher dose to achieve the same visual contrast as 10–12 oz/yd² fabric, but higher dose also increases the risk of pocket and seam abrasion. Sulphur-dyed weft and reactive dyed embroidery show staining differently from indigo; pockets made of polyester-cotton poplin are more prone to visible indigo redeposition than cotton twill pockets. The enzyme bath should be prepared with softened water, because hardness above 150 ppm CaCO₃ can form calcium salts with anionic dye particles and may lower the efficiency of anti-redeposition surfactants. Production-scale drum washers with direct steam injection can produce local hot zones, so the temperature probe should be placed in the liquid sump rather than in the steam path. Full-scale batch records show that residual cellulase from previous loads can contaminate the next batch when the drain and rinse sequence is shortened; this residual carryover is a common cause of excess tensile loss in pale-dyed lots.

Why Does Acidic Cellulase Activity Collapse Past 55°C in Cotton Wet Processing?

The thermal half-life of Trichoderma-derived acidic cellulase in a textile bath drops sharply once the setpoint exceeds 55°C. Biopolishing is therefore run at 45–50°C, even though higher temperatures would theoretically increase hydrolysis rate. The process objective is not bulk weight loss but controlled surface defibrillation; harsher conditions produce a measurable drop in fabric strength without additional pilling improvement. Biopolishing is normally performed on knitted cotton or cotton-blend fabrics after dyeing, in a jet or softflow machine where rope circulation at 200–250 m/min delivers mechanical shear. The bath is buffered to pH 4.8–5.2, and the enzyme dose ranges from 0.25–0.75% owf for a standard endoglucanase-rich product; contact time is 30–60 min. Under these conditions, surface fuzz and immature cotton fibre ends are removed, and the pilling grade measured by ISO 12945-2:2020 commonly rises from 2–3 to 4–5. Breaking strength retention is measured by ISO 13934-1:2013 or ASTM D5034-21; on single jersey cotton knits, a loss of 5–12% is typical, while higher doses or longer running times create preferential attack at loop intersections and can cause needle-line tears. The bath is then drained, the fabric is rinsed at pH 9.0–10.0, and inactivation is verified by testing a residual soak solution with CMC viscosity reduction.

Operating outside the stated pH window is not a simple trade-off. Above pH 6.0, acidic cellulase activity declines and the bath conditions favour indigo redeposition in denim applications; below pH 4.0, acid hydrolysis of cellulose contributes to strength loss. In bulk production, water hardness above 150 ppm calcium carbonate can buffer the bath and shift the measured pH upward; the pH setpoint must be checked after fabric loading, not only before enzyme dosing. Cellulase products that claim biopolishing performance must be evaluated by the ratio of endoglucanase to exoglucanase activity; products with high cellobiohydrolase content create excessive tensile loss. The bath can be reused only if the enzyme activity after one cycle is measured by CMC assay and the pH is re-buffered. In practice, most cotton knit finishers do not reuse enzyme baths because the hydrolytic activity remaining after one 60-min cycle is below 30% of the initial dose, and the accumulation of fibre detritus increases pilling rather than reducing it. When biopolishing is combined with optical brighteners, the brightener should be added after enzyme inactivation, because the acidic bath and residual protein can reduce brightener substantivity.

When Lyocell Primary Fibrillation Must Be Removed Before Dyeing

When lyocell fabric enters the first wet process, mechanical abrasion in rope form releases surface fibrils that are longer and more visible than the short fuzz found on cotton. Primary fibrillation is a characteristic failure mode of lyocell processing, and an acidic cellulase bath at 50–55°C and pH 4.5–5.0 is used to remove the fibrils before dyeing. The fabric is processed in a winch or air-jet machine with a low-tension drive, because high rope tension concentrates abrasion at crease marks and produces secondary fibrillation later in the dye cycle. The dose is generally 0.5–1.0% owf of a liquid acid cellulase, and the exposure time is 30–45 min; the end point is judged by fibre surface inspection under a 10× microscope or by reduction in stack dye uptake after a control dyeing. Over-treatment reduces wet abrasion resistance and can strip dyed lyocell surfaces. After the defibrillation step, the enzyme must be deactivated with alkali at pH 9.0–10.0 and a rinse at 70–80°C. If residual cellulase remains in the fabric, it migrates into the dye bath and causes shade variability. Production records from air-jet equipment show that batch-to-batch variation in lyocell fibrillation is influenced by upstream yarn twist and fabric construction; therefore, the enzyme dose cannot be fixed without a first-batch trial.

Secondary fibrillation after dyeing is not controlled by enzyme alone; a crosslinking or resin finishing step is required after the washdown. In some processes, acid cellulase is used twice: once before dyeing to remove primary fibrils and once after dyeing at a lower dose to clean secondary fibrils. The second treatment is limited to 15–20 min to avoid shade change on fully dyed fabric. Fabric processed in rope form can develop crease marks at the point where the rope folds over the lifter reel; some mills switch to open-width processing to reduce this localised mechanical attack. Published data for this specific configuration is limited, and the process is typically calibrated to the fabric supplier's pilling or fibrillation index.

Lignocellulosic Saccharification at 20% Dry Matter and the Mixing Constraint

Pretreatment determines whether a cellulase can reach its substrate; dilute-acid pretreatment removes most hemicellulose but leaves a lignin-rich residue that competes for enzyme binding. Acidic cellulase is used in lignocellulosic ethanol and biochemical production because its optimum range of pH 4.8–5.2 and 45–55°C matches the tolerance window of Trichoderma longibrachiatum-derived cocktails. The reaction mixture is buffered with citrate at 50 mM, and the feedstock is loaded at 15–20% insoluble solids for stirred-tank hydrolysis. At 20% dry matter, the slurry exhibits yield stress and shear-thinning behaviour; apparent viscosity above 1,000 mPa·s at 10 s⁻¹ is commonly reported for pretreated corn stover. Continuous mixing at laboratory scale is not representative of full-scale horizontal reactors equipped with helical or puddle impellers. Intermittent mixing of 10 min on and 20 min off is used to reduce power draw and preserve enzyme activity at the air-liquid interface, where cellulase can denature. The enzyme load must be expressed as filter paper units per gram of cellulose, typically 10–30 FPU/g cellulose for washed substrates, but direct comparison across suppliers is unreliable because β-glucosidase content varies.

End-product inhibition is the dominant process conflict: cellobiose concentrations above 5 g/L inhibit cellobiohydrolase activity, and glucose above 30 g/L exerts feedback inhibition on β-glucosidase. Therefore, a β-glucosidase-rich accessory enzyme or a co-fermenting organism is required. Simultaneous saccharification and fermentation is run at 35–37°C, which is below the 50°C optimum of the cellulase and reduces hydrolysis rate by 40–60%. Separate hydrolysis and fermentation avoids this temperature compromise but allows glucose to accumulate to inhibitory levels. Pilot-scale data from dilute-acid pretreated corn stover report glucose yields of 70–85% after 72 h at 15% solids, but yields at 30% solids are lower because of mass transfer restrictions and higher viscosity. Feedstock variability is a larger source of yield loss than enzyme formulation. Lot-to-lot differences in pretreatment severity, xylan content, ash and lignin condensation change the non-productive binding capacity of the substrate. Enzyme doses should be adjusted on a dry-matter basis and checked against blank hydrolysis of a reference substrate, such as filter paper or Avicel. Inhibitor carryover from pretreatment, including acetic acid, furfural and 5-hydroxymethylfurfural, reduces cellulase activity at concentrations above 1 g/L for acetic acid and above 0.1 g/L for furfural. Detoxification by washing or overlime can remove inhibitors but also adds water, and the benefit must be weighed against increased process flow and waste treatment. In continuous high-solids reactors, localised pH pockets form because the buffer capacity is consumed by acid groups released from the substrate; pH setpoint should be checked at multiple probe locations and adjusted with sodium hydroxide, not assumed uniform at 15% solids.

For recycled linerboard furnish, an endoglucanase-rich acidic cellulase can be metered into the stock preparation line at 0.02–0.10% on oven-dry pulp. The treatment is run at pH 5.0 and 50°C for 20–30 min to remove surface fibrils and fines from the fibre surface, which increases drainage and reduces steam demand in the dryer section. Freeness is measured by TAPPI/ANSI T 227 om-17; production mills typically observe an increase of 30–80 mL CSF, but the result is highly dependent on ash content and fibre source. The main operational boundary is fibre strength: doses above 0.1% on oven-dry pulp produce a measurable loss in tensile index measured by TAPPI T 494 om-13. This application is less commercially established than textile biopolishing, and published mill data for acidic cellulase in recycled linerboard is limited.

Cellulase-Assisted Extraction in Low-pH Enological Matrices

Most enological enzyme preparations are pectinase-dominant, and the acid cellulase contribution is frequently described only as side activity in technical dossiers. Grape maceration occurs at pH 3.2–3.8 and 20–30°C, which lies below the pH 4.5–5.0 optimum of standard acidic cellulase. Cellulase activity at pH 3.5 is therefore reduced, and a product intended for winemaking requires an acidophilic strain, commonly Aspergillus niger, with retained endoglucanase activity at low pH. The enzyme is added to the must at the start of maceration to reduce the viscosity contribution of cell wall fragments and to improve the release of colour and tannin from skin cells. However, commercially available oenological cellulase preparations are not standardised by endoglucanase activity alone, and published data for acidic cellulase as a single component in red wine maceration is limited. Trial addition at 1–3 g/hL of the formulated enzyme product is common industry practice, but the response varies with grape variety, rot level, and maceration time. The process does not have the narrow pH control of textile applications because the must pH is fixed by the fruit and cannot be shifted into the cellulase optimum without altering wine chemistry. In low-pH white juice clarification, the same limitation applies; the enzyme must be selected for activity at 15–20°C and not only by its pH optimum at 50°C.