Silk is one of the oldest and most prized natural fibres in the world, but the journey from a silkworm’s cocoon to a usable thread is far more technical than most people realize. Silk reeling is the industrial process of unwinding continuous filaments from silkworm cocoons and combining them into raw silk yarn – the very foundation of every silk fabric. It is not a single action but a carefully sequenced series of steps, each one protecting the integrity of the filament and minimizing waste. Understanding this process reveals why high-quality silk commands such value and why every stage demands precision.
Table of Contents
What is silk reeling?
Silk reeling is the process by which filaments from multiple cooked cocoons are drawn together and wound onto a reel to produce a single, composite thread of raw silk. A single filament from one cocoon is far too fine to use on its own – filaments from anywhere between 2 and 20 cocoons are combined during reeling to achieve the desired thread thickness, or denier. Poor reeling practices lead to uneven threads, knots, and weak spots that directly compromise fabric quality. Every step in the process – from stifling to re-reeling – exists to prevent exactly these problems.
Step 1: Cocoon stifling
The first step is stifling, which means killing the pupa inside the cocoon before it develops into a moth. If the pupa is allowed to emerge, the adult moth pierces the cocoon shell, severing the continuous filament and making the cocoon impossible to reel. Stifling must therefore happen within a narrow window – cocoons contain live pupae that will emerge within 10-12 days of cocooning, so timely processing is essential.
Methods of stifling
Common stifling methods include sun drying, steam stifling, hot air drying, and infrared irradiation. Sun drying is the most traditional approach but has drawbacks – prolonged UV exposure can degrade silk quality, and cloudy weather makes it unreliable. Steam stifling is fast and widely used, but steam-stifled cocoons cannot be reeled immediately, as wet sericin causes the fibroin to clump. Hot air drying, now favoured in advanced sericulture countries, improves reeling performance and raw silk yield, and also allows cocoons to be stored for longer periods without quality loss. After stifling, stifled cocoons can be preserved for up to 6 months if stored correctly – in well-ventilated rooms with humidity not exceeding 70% and protected from insects and fungal attack.
Step 2: Sorting and grading
Once stifled, cocoons go through sorting. Only cocoons of similar quality are grouped together for reeling, since mixing different grades creates inconsistency in the final thread. Sorting removes cocoons that are damaged, stained, double (two pupae spinning together), thin-shelled, perforated, or irregular in shape. The objective is to ensure only good cocoons with uniform size, shape, and shell thickness proceed to reeling.
This step also involves cocoon mixing or blending – combining lots of similar quality from different batches to maintain uniformity in denier throughout the reeling run. Cocoon quality contributes to roughly 80% of both productivity and quality in silk reeling, making careful sorting one of the highest-impact steps in the entire process.
Step 3: Cocoon cooking
Before any filament can be drawn, the cocoon must be softened in hot water – a step called cooking or cocoon boiling. Silk consists of two proteins: fibroin, the inner structural filament, and sericin, the gum-like outer coating that binds the filament layers together. Sustained heat processing softens the hardened sericin so that the filament can be unwound without snapping.
Cooking methods
The main cooking methods are single pan (open pan) cooking, two-pan or three-pan cooking, and pressurized conveyor cooking. In the open pan method – the most conventional approach – cocoons are cooked in water maintained at 95-97°C for 10-15 minutes. Two-pan and three-pan systems are batch processes where cocoons are moved through tanks at progressively controlled temperatures, allowing for better sericin softening without over-processing. Crucially, the water used for cooking must be colourless, odourless, transparent, and maintained at a pH between 6.8 and 8.4 – impurities in the water adhere to the silk and directly affect its colour and lustre. It takes approximately 50-150 litres of water to produce just one kilogram of raw silk.
Step 4: Deflossing and brushing
After cooking, cocoons are covered in a tangled outer layer of loose, broken fibres called floss. Deflossing is the removal of this unreelable mass of silk from the cocoon surface to expose the actual reeling end – the point from which the continuous filament begins. Without deflossing, the reeling end cannot be found and the reeling process cannot begin.
Once deflossed, the cocoons are brushed – either by hand or using a mechanical brush – to locate and isolate the true end of the continuous filament. The exterior loose floss is brushed away, and the filament end is then picked up and transferred to the reeling device. In India, deflossing is mostly done by peeling off the floss layer by hand, though simple bamboo brushes are also used to save time. Semi-automatic and automatic reeling machines include mechanical brushing devices integrated into the machine itself. This step requires care – brushing too aggressively breaks the filament, while insufficient brushing leaves floss in the thread, introducing defects downstream.
Step 5: Reeling
Reeling is the process of unwinding the silk filament from the cocoon and winding it onto a reel. The reeling ends from multiple cocoons are picked up, combined, and passed through a device called a croissure before being wound onto the reel. The croissure twists the combined filaments into a series of spirals, agglutinating them firmly together with sericin, squeezing out excess water, and creating a round, smooth, compact thread. This interlinking is what holds the multi-filament thread together for all subsequent processing.
Reeling machines
Three main types of reeling systems are used, particularly in India:
- Charka reeling: A traditional, hand-operated system in which cooking and reeling are done in the same basin. It uses a simple chambon-type croissure and is operated by two people. It is used for inferior or defective cocoons and produces lower-quality silk with uneven denier.
- Cottage basin reeling: Here, cooking and reeling are separated into different basins. It uses a travellette croissure with three pulleys for better thread formation and water removal, producing significantly better silk than charka.
- Multi-end filature reeling: A power-driven system with multiple ends per machine and the most sophisticated croissure mechanism. Continuous reeling is possible in this modern device, and it produces the highest quality raw silk with consistent denier.
Throughout reeling, the cocoons remain in hot water. When one cocoon is exhausted, another is immediately added to maintain a continuous, uniform yarn – this substitution requires constant attention from the operator. An efficient reeler maintains a fixed number of cocoons per end at all times to keep denier consistent.
Step 6: Re-reeling
The raw silk wound onto small reels during reeling is not yet in a form suitable for marketing or weaving. Re-reeling transfers this silk onto large standard reels and is the final step in the reeling process. The standard reel has a circumference of 150 cm, and re-reeling adjusts the width and weight of the skein to meet this international standard. Beyond standardization, re-reeling serves a quality function: it eliminates gum spots, ties up loose ends from broken filaments during reeling, and identifies any remaining defects.
The optimum re-reeling speed is 150-170 revolutions per minute for 21-denier silk, and the process is carried out under controlled temperature and humidity – around 41°C and 36% relative humidity – to prevent the skeins from sticking together after drying. Before re-reeling begins, the hardened sericin on the small reels is softened by dipping or applying a wet cloth, which helps the filament transfer smoothly. Using a wetting agent such as Turkey red oil and maintaining a uniform skein drying temperature of 40°C during re-reeling further enhances yarn quality.
After re-reeling, the skeins go through lacing – a thread is passed across the skein at multiple points to keep the filaments in place and prevent tangling during subsequent handling. Five interlacings at three places on the skein are the recommended standard. The laced skeins are then skeined – twisted and folded to form compact spirals – before being bundled into books for packing and dispatch.
Waste minimization and quality control
Silk reeling is resource-intensive, and waste is a persistent concern. Reelability – the percentage of a cocoon’s filament that can actually be reeled – ranges from 40 to 80% depending on the cocoon variety, and stained cocoons consistently show poor reelability. Even unusable cocoon material is not entirely wasted: by-products from reeling include cocoon waste and pupae, which are rich in protein and used as feed for poultry and fish, or processed for oil extraction.
Key quality factors throughout the process include water temperature during cooking and reeling, reel speed and thread tension, operator skill, and the accuracy of cocoon feeding to maintain consistent denier. Defects in raw silk are classified as super major, major, or neatness defects, and all arise from conditions during reeling – reinforcing that each step is interconnected and none can be performed carelessly without consequences for the final product.
What do you think? Given that cocoon quality accounts for as much as 80% of reeling productivity and raw silk quality, how much can improvements in reeling technology alone compensate for poor-quality cocoon inputs? And as modern automated reeling machines continue to replace traditional charkha and cottage basin systems, what happens to the knowledge and livelihoods of skilled hand-reelers in rural sericulture communities?
References
- https://www.pandasilk.com/overview-of-silk-reeling/
- https://www.fao.org/4/x2099e/x2099e07.htm
- https://lalouettesilk.com/blog/how-is-silk-made/
- https://indiaagronet.com/indiaagronet/sericulture/contents/Raw%20Silk.htm
- https://www.slideshow.com/slideshow/sericulture-post-cocoon-technology-processing-of-cocoons/249532007
- https://kssrdi.karnataka.gov.in/page/Contributions/Silk+Reeling+and+Fabric+Manufacturing/en
- https://www.notesonzoology.com/sericulture/production-of-silk-9-processes/250
- https://silks.csb.gov.in/pune/wp-content/themes/Common_District/poc-frame.html
- https://www.scribd.com/document/649538817/Silk-Reeling
- https://www.fao.org/4/x2099e/x2099e08.htm
- https://www.fao.org/4/x2099e/ftpmirror.your.org/pub/misc/cd3wd/1005/_ag_silk_reeling_testing_unfao_en_lp_116630_.pdf
- https://sericulture-activities.blogspot.com/2017/10/reeling-spinning-of-silk-yarn.html
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