How to Boil Cocoons (Preparation for Silk Floss Making)

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Purpose: A pre-treatment to partially remove the cocoon’s outer protein, sericin, and make the layers easier to open into fluffy sheets.
Sericin dissolves more readily with heat + alkali, but overdoing it weakens the silk core (fibroin). Careful control of temperature, time, and concentration is essential.

Contents

  1. Pre-Soak (Wet-Out)
  2. Recipes (Baking Soda / Soda Ash)
  3. Rinsing & Neutralization
  4. How to Judge the Endpoint
  5. Science Notes (Sericin & pH)
  6. Safety & Environmental Care
  7. Related Links
  8. FAQ

Note: Long time / high temperature / strong alkali can damage fibers.
The temperatures, times, and concentrations here reflect our studio’s practice.

Pre-Soak (Wet-Out)

Dry cocoons tend to float and process unevenly. Before boiling, fully hydrate them.

  • Soak in warm water for 30–60 min (overnight pre-soak also works).
  • Gently press them under so water reaches the interior of each cocoon.
Hydrating cocoons before alkaline boil
Once hydrated, cocoons sink more easily and boil more evenly.

Recipes (Baking Soda / Soda Ash)

We switch between a gentler baking soda (NaHCO₃) bath and a shorter soda ash (Na₂CO₃) bath depending on the job.

How we express quantities: We standardize by g/L (bath concentration) and liquor ratio.
Guideline: 500 g cocoons : 10 L water (≈ 1:20 liquor ratio).

Recipe A: Baking Soda (NaHCO₃) + Soap Flakes — gentle & unhurried

  • Cocoons: 500 g
  • Water: 10 L (≈ 1:20)
  • Baking soda: 6 g/L (→ 60 g / 10 L)
  • Soap flakes: 1 g/L (→ 10 g / 10 L)  *≥80% pure soap recommended
  • Temp & time: 90–95 °C for 60–90 min (maintain a quiet near-boil)
  • Agitation: Occasionally turn gently to prevent uneven processing

Tip: Weak alkali is kinder to fibers but needs more time. Result tends to be loftier, softer.

Recipe B: Soda Ash (Na₂CO₃) + Soap Flakes — shorter & standard

  • Cocoons: 500 g
  • Water: 10 L (≈ 1:20)
  • Soda ash: 2 g/L (→ 20 g / 10 L)
  • Soap flakes: 1 g/L (→ 10 g / 10 L)
  • Temp & time: 95–98 °C for 30–45 min
  • Agitation: Occasionally turn gently

Caution: Soda ash is a stronger alkali. Do not overshoot temperature or time.
When endpoint is reached, lift out and rinse promptly.

Rinsing & Neutralization (Finishing Touch)

  • Warm rinses: 50–60 °C for 10–20 min × 2, or until thoroughly rinsed.
  • Neutralizing rinse (recommended): Dip for 2–3 min in lukewarm water with citric acid 1 g/L (or a dash of vinegar), then lightly re-rinse.
    └ Reduces residual alkali, lowering risks of uneven dyeing or yellowing later.
Quick neutralizing rinse after alkaline boil
Neutralizing rinse should be brief—no need for harsh acidity.

How to Judge the Endpoint

(Before full rinsing, take out one cocoon, rinse with water, and check.)

  • When pinched lightly, it doesn’t spring back and thin layers peel apart gently.
  • The shell feels supple and layers open evenly.
  • Foam subsides a bit and the bath looks slightly cloudy (sericin released).
Layers open smoothly—time to stop
If the layers open willingly, you’ve reached the endpoint. Lifting out now preserves quality.

Science Notes (Sericin & pH)

Sericin is a protein rich in hydrophilic amino acids; it dissolves more readily with heat + alkali.
Fibroin, by contrast, hydrolyzes in hot alkali, lowering molecular weight and thus strength.
Therefore, temperature, time, and pH control is the key to quality.

  • Baking soda (NaHCO₃): bath pH is typically mildly alkaline (≈ pH 8).
  • Soda ash (Na₂CO₃): gives a higher pH at the same g/L (toward strong alkali).

Safety & Environmental Care

  • PPE: Heat-resistant gloves, apron, and good ventilation.
  • Waste bath: Dilute well and adjust toward near-neutral with citric acid or vinegar before discharge.
  • Solids: Pupae and cocoon residues → compost.

FAQ

Q. Which should I choose—baking soda or soda ash?
A. Choose by time and hand. Baking soda is gentler but longer; soda ash is quicker but demands tighter control.

Q. Why add soap?
A. Soap acts as a surfactant: it lifts soils and improves wet-out on water-shedding cocoons, helping sericin dissolve evenly and reducing re-deposition. Traditionally, soap + carbonate (baking soda or soda ash) has been widely used for scouring/degumming.

Q. How far should I remove sericin?
A. For mawata, just enough for the layers to open smoothly. Prolonged heating risks loss of feel and strength—stop on the early side.

Q. How should I handle wastewater?
A. Dilute thoroughly and adjust to near-neutral before discharge. Solids go to compost or appropriate waste. Follow local regulations.