Maximizing Reeling Waste for Spun Silk and More

When silk cocoons are unwound during reeling, the process doesn’t just produce premium raw silk – it generates a substantial volume of waste material at every stage. Far from being discarded, this reeling waste forms the backbone of the spun silk industry and feeds into cosmetics, animal nutrition, and even human food systems. Understanding these by-products reveals how sericulture achieves near-zero waste across the entire production chain.

What are the by-products of silk reeling? 🔗

The chief by-products of the reeling industry are silk wastes obtained at different stages of processing cocoons into raw silk, along with the pupae left inside each cocoon. These materials are not mere leftovers – they carry genuine commercial value and are actively traded as raw materials for downstream industries. The wastes generated during reeling are broadly grouped into three categories: cocoon waste, reeling waste, and winding waste.

Cocoon waste 🔗

Not all cocoons in a batch are suitable for continuous reeling. Damaged, double, undersized, or stifled cocoons that cannot yield a clean continuous filament are set aside as cocoon waste. Double cocoons, produced by two silkworms spinning together, are processed separately to make doupion silk – a coarser, textured yarn valued for its irregular character. Other rejected cocoons feed directly into the spun silk supply chain.

Floss 🔗

Floss is the outermost layer of the cocoon – a protective, non-continuous covering that must be removed before reeling begins. Because this layer lacks a continuous filament, it cannot be reeled in the conventional sense. Instead, floss is collected separately and used as a primary raw material for spun silk production. Floss silk can be manufactured from any kind of cocoon, principally from pierced, end-missing, and double cocoons, and is also used as padding against cold weather and as the basis for hand-spun yarns.

Reeler’s waste 🔗

During the actual reeling operation, filaments break frequently and must be re-attached. The discarded snippets from these breaks, the tangled ends found during brushing, and the thin inner filament closest to the pupa – all of this constitutes reeler’s waste. During the process of reeling from the cocoon, the silk often breaks; and both in finding a true and reliable thread, and in joining the ends, there is unavoidable waste. Raw silk that is re-reeled also produces additional discarded material known as gum-waste. All of this material, though short and irregular in fibre length, retains the fundamental qualities of silk fibre and is recoverable for spinning.

From waste to spun silk yarn 🔗

Short lengths of inferior silk filaments taken from waste material are combed and spun together as silk thread – this is spun silk. The conversion of reeling waste into spun silk yarn is a well-established industrial process, and it produces a hierarchy of yarn grades, each with distinct properties and end uses.

Schappe silk 🔗

Schappe is the higher grade of spun silk yarn. It is produced from the better-quality waste – longer filaments from deflossed cocoons, broken reeling ends, and clean pierced cocoons. These short filaments are aligned, brushed, and spun into a fairly regular schappe yarn. The degumming in schappe production is achieved through a fermentation process (schapping), which removes the sericin gum while preserving fibre integrity. The result is a yarn that is soft, moderately lustrous, and suitable for fine fabrics including velvet and dress linings. Spun silk is used for shantung, pile fabrics, dress trimmings and linings, elastic webbing, sewing silk, summer weight silks, velvets, umbrella fabrics and insulation.

Bourette silk (noil silk) 🔗

The schappe spinning process itself produces by-products that are further processed into bourette yarn – also widely known as noil silk. Bourette is made from the shortest fibres left after combing during spun silk production, and it retains more of the sericin gum, giving it a rougher, more textured handle. Bourette silk is matte and coarse, but it is more voluminous and durable than other silks, and also warmer. Despite its lower lustre, it retains the core benefits of silk – breathability, light weight, and antibacterial properties – and its nubby, slubbed texture has made it a popular choice for fashion fabrics, upholstery, and draperies.

How spun silk compares to reeled silk 🔗

Spun silk threads are soft but less lustrous, strong, and elastic than reeled silks, because the shorter staple used in spinning cannot match the continuity and alignment of a reeled filament. However, spun silk is significantly less expensive, making it accessible for a wider range of textile applications. It possesses all the general characteristics of reeled silk – warmth, drape, and dye affinity – at a more economical price point.

Dead pupae: the most versatile by-product 🔗

Every cocoon that is reeled yields a dead pupa inside. For every 1 kg of raw silk produced, approximately 8 kg of wet or 2 kg of dry silkworm pupae are generated as a waste by-product. At industrial scale, this represents an enormous volume of biomass. Rather than treating this as a disposal problem, sericulture-producing countries have developed multiple applications for pupae across food, feed, cosmetics, and agriculture.

Silkworm pupae as animal feed 🔗

Silkworm pupae are very rich in protein and fat content and are used as feed for cattle, fish, and poultry. Research has consistently supported this application. Studies suggest that silkworm pupae can partially replace fish meal or soybean meal in diets for animals such as poultry, fish, and rabbits. The high protein digestibility and favourable amino acid profile make pupae meal a cost-effective and nutritionally sound substitute for conventional protein sources in animal husbandry and aquaculture.

Silkworm pupae as human food 🔗

Domestic silkworm pupae are an important by-product of sericulture and have a long history as food and feed ingredients in East Asia. Their nutritional credentials are strong. Silkworm pupae consist of 18 amino acids including all essential amino acids, approximately 62% protein, around 30% fatty acids, along with vitamins and minerals, and contain a higher amount of calorigenic nutrients compared to other conventional food. In parts of China, Korea, and the northeastern states of India, cooked or dried pupae have been consumed for generations. They are also incorporated into protein supplements, bakery products, and processed snack foods.

Pupae oil in cosmetics and pharmaceuticals 🔗

Silkworm pupae oil is viewed as a reliable source with a variety of applications in the food and pharmaceutical sectors, and can also have possible cosmetic applications. The high fat content – over 30% on a dry matter basis – makes pupae a viable raw material for extracting chrysalis oil, which is used to formulate creams, soaps, lotions, and emulsions. The antioxidant properties found in the insect have spurred the evaluation of pupae protein concentrate for the development of anti-aging cosmetic products and for the elimination of shallow wrinkles or skin whitening. In sericultural countries like Japan, pupae-based pupal cakes are also produced and marketed for their nutritional content.

Pupae oil extraction and other industrial uses 🔗

In many sericultural countries, oil is extracted from pupae by expression or by solvent extraction. This oil is rich in alpha-linolenic acid (ALA), an omega-3 fatty acid. Both n-3 and n-6 fatty acids present in pupae oil as primary components are crucial for treating diabetes and cardiovascular disorders. Beyond oil, the pupal exoskeleton is a source of chitin – a structural polysaccharide with applications in food technology, wound dressings, and pharmaceutical film coatings. The residual defatted meal after oil extraction is used as a protein-rich fertiliser or incorporated into animal feed.

Sericin: the gum in the wastewater 🔗

One more by-product of reeling deserves mention. When cocoons are cooked and degummed, the sericin protein dissolves into the reeling water. Specialised protein extracts such as sericin and fibroin obtained from silk processing have gained commercial importance in cosmetics, pharmaceuticals, wound healing products, edible films, and tissue engineering scaffolds. Sericin recovery from reeling wastewater is an active area of research, aimed at transforming what was once an effluent problem into a commercial opportunity for high-value bioactive compounds.

Economic significance of reeling by-products 🔗

The by-products of reeling are not a marginal concern – they are a substantial revenue stream. These are valuable materials giving substantial returns to the reelers through their sale. For small and marginal reelers, the income from selling cocoon waste, pupae, and floss to downstream processors can represent a meaningful share of total earnings. At the industry level, recognising these outputs as co-products rather than waste enhances the economic viability of the entire sericulture value chain. Silk reeling and spinning generate waste such as floss silk, noil, and short fibres, which are repurposed into spun yarn, nonwoven fabrics, upholstery, and insulation materials – demonstrating just how deeply these by-products are embedded in commercial textile supply chains.

The reeling stage of sericulture is a reminder that in well-managed agro-industrial systems, the concept of waste is relative. Floss becomes fashion fabric. Pupae become protein. Even the cooking water becomes a source of bioactive compounds. Every gram of the cocoon is accounted for.

What do you think? Given that silkworm pupae are nutritionally comparable to conventional protein sources, do you think greater adoption of pupae-based food products is realistic in regions where insect consumption is not yet mainstream? And as the spun silk industry depends entirely on reeling waste, how might changes in reeling efficiency – such as improved automated machines that recover more filament – affect the availability of raw material for spun yarn production?

References

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