Soaking and Cooking

Part of Paper Making

Breaking down raw plant material through water soaking and alkaline cooking — the chemical preparation that makes fiber ready for beating and sheet formation.

Why This Matters

Plant fibers suitable for papermaking are locked inside a matrix of non-cellulose materials: lignin (a phenolic polymer that binds cells together), pectin (a polysaccharide in cell walls), waxes, oils, and other extractives. Raw plant material cannot be beaten into papermaking pulp — it is too stiff, the fiber bundles are too tightly bound, and the non-cellulose materials would contaminate the final paper, causing it to discolor and degrade rapidly.

Soaking and cooking dissolves or softens these binding materials, freeing cellulose fiber from the surrounding matrix. After cooking, individual fibers can be separated with light mechanical work — the beating step that follows is then doing useful work on already-loosened fiber, not fighting against the original plant structure.

Understanding soaking and cooking means understanding alkali chemistry at a basic level — why wood ash lye works, how to make it, how strong it needs to be for different materials, and how to tell when cooking is complete. This is practical chemistry that your community can perform with materials available from fire residue and water alone, producing one of the most valuable substrates for preserving knowledge.

The Chemistry of Alkaline Cooking (Simplified)

Lignin and pectin are susceptible to attack by alkali (high pH) solutions. When plant material is immersed in hot alkali solution, the alkali molecules react with the chemical bonds holding lignin and pectin together, breaking them into smaller, water-soluble fragments that wash away.

Cellulose, the target fiber, is much more resistant to alkali attack — this is why alkaline cooking can dissolve the binding matrix while leaving the fibers largely intact, provided the alkali is not too strong or the cooking too prolonged.

The alkali used in traditional papermaking is wood ash lye — a solution of potassium carbonate (K2CO3) and potassium hydroxide (KOH) made by leaching water through wood ash. These compounds are mildly to moderately alkaline, effective at loosening plant fiber with moderate cooking times without severely damaging the cellulose.

Stronger alkali (stronger lye, or commercial sodium hydroxide / caustic soda if available) loosens fiber faster but requires shorter cooking times and more careful rinsing to avoid over-cooking. Start with weaker solutions until you understand your specific fiber sources.

Making Wood Ash Lye

Wood ash lye is made by passing water through a bed of wood ash, extracting the soluble potassium compounds.

Ash source: Hardwood ash (oak, beech, maple, ash tree) produces stronger lye than softwood ash. Straw and grass ash also work. Do not use coal ash — it contains sulfur compounds that damage fiber.

Leaching setup:

1. Line a wooden barrel, clay pot, or wicker basket with a layer of straw or clean cloth to act as a filter.
2. Fill with dry wood ash to within 10 to 15 cm of the rim.
3. Pour warm water over the ash. Allow it to soak through completely.
4. Collect the liquid that drains from the bottom — this is lye.
5. Pass this liquid through the ash bed again (recirculation strengthens it).
6. Repeat 3 to 5 passes to produce a useful concentration.

Testing lye strength: Several traditional tests:

• Egg float: A fresh egg floated in the lye solution should sink just below the surface, with a spot approximately 2 cm across remaining above the waterline. If the egg sinks completely, lye is too weak. If it floats high with more than 5 cm above surface, lye is too strong for most papermaking purposes.
• Feather test: Dip a feather in the solution. Moderately strong lye (useful for papermaking) will soften but not immediately dissolve the feather. Very strong lye (too strong for most paper fiber) will dissolve the feather rapidly.
• Feel: Lye solution feels slippery between fingers. Very weak lye (dilute enough to be safe for cooking) has only a slight slipperiness. Strong lye has pronounced slipperiness — use caution, as strong lye causes chemical burns.

Safety: Lye solution is caustic at working concentrations. Avoid contact with eyes. Wear improvised eye protection (a strip of bark or wood above the eyes as a brow shield) when pouring. Rinse skin contact immediately with large amounts of water.

Soaking: Pre-Treatment Before Cooking

Before cooking, soak your plant material in plain water. This preliminary soaking serves several functions:

• Rehydrates dried plant material, allowing it to absorb cooking solution uniformly
• Begins softening surface layers
• Leaches some water-soluble extractives without requiring heat or alkali
• For old rags, loosens accumulated dirt and grease

Soaking time:

• Old rags and rope: 2 to 8 hours in cold water
• Dry plant stalks (flax, hemp, nettle): 12 to 24 hours
• Fresh plant material: 2 to 4 hours

Change soaking water once or twice for heavily contaminated materials (old rope, rags with accumulated oil). The discarded soaking water carries away water-soluble impurities that would otherwise end up in your paper.

Retting (extended soaking): For fresh plant stems, retting — controlled microbial decomposition in standing water over 1 to 4 weeks — further breaks down pectin in the outer stalk layers without cooking. After retting, cooking time is reduced significantly. This is worth doing when fresh plant stems are your primary raw material. See Plant Fibers for more detail on retting specific plants.

Cooking: Step by Step

Setting Up the Cook Pot

Use a large pot or vessel — clay, stone, or metal all work. Avoid copper or uncoated iron for final cooking of paper fiber: copper turns fiber green; iron can discolor fiber and introduce iron compounds that cause eventual paper staining. A clay pot, stone-lined firepit vessel, or wooden barrel that has been made waterproof with pitch all work well.

Capacity should be at least 3 to 4 times the dry volume of fiber to be cooked — the fiber expands as it absorbs liquid, and you need enough liquid to keep everything submerged.

Lye Concentration by Fiber Type

Material	Lye Strength	Notes
Old cotton rags	Very weak (barely slippery)	Short fibers, easily damaged
Old linen rags	Weak	May use plain water for aged, soft rags
New cotton cloth	Weak to moderate
Old hemp rope	Moderate
Flax or hemp straw	Moderate	Cook longer than rags
Nettle stems	Moderate	Outer green layer requires cooking
Cattail leaves	Moderate to strong	Tough outer cuticle
Bamboo	Strong	Silica-rich outer layer needs aggressive treatment

Cooking Process

1. Place pre-soaked fiber in the cooking vessel.
2. Add lye solution to cover fiber by 5 to 10 cm.
3. Bring to a gentle simmer over fire. Do not boil vigorously — turbulent boiling causes fiber tangling and can splash hot lye.
4. Maintain a gentle simmer (small bubbles visible, occasional stirring of the surface).
5. Stir occasionally with a long wooden paddle to ensure even treatment. Unstirred fiber may have an over-cooked outer layer and under-cooked interior.
6. Check progress every 30 minutes by removing a small bundle of fiber with a stick and attempting to separate it with your fingers.

Readiness test: The fiber is ready when individual strands separate readily with light finger pressure, and the fiber feels silky or slippery rather than stiff. A well-cooked fiber bundle should pull apart into individual strands without tearing. Under-cooked fiber resists separation and requires more cooking. Over-cooked fiber may feel almost slimy and fall apart into very short fragments.

Typical Cooking Times

Material	Time at Simmer
Old soft cotton rags	30 to 60 minutes
Old linen rags	1 to 2 hours
Hemp rope (old)	1.5 to 3 hours
Flax straw	2 to 4 hours
Nettle (fresh)	1 to 2 hours
Cattail leaves	2 to 4 hours
Bamboo (young shoots)	3 to 6 hours

These are starting points. Variables (lye strength, fire intensity, fiber age) mean you must test frequently rather than rely solely on time.

Rinsing After Cooking

After cooking, the fiber must be thoroughly rinsed to remove alkali residue. Alkali remaining in the paper will continue to attack cellulose over time — not quickly enough to be visible immediately, but over years to decades it weakens the paper and may cause discoloration.

Rinsing procedure:

1. Transfer cooked fiber from the cook pot to a rinsing container (any vessel large enough to work in).
2. Cover with fresh cold or warm water. Squeeze and work the fiber with your hands to expel cooking liquor.
3. Drain and repeat. At minimum, rinse 3 to 4 times, squeezing firmly between each rinse.
4. Continue until the rinse water runs essentially clear and the fiber no longer has a chemical smell or slippery feel.

Testing completeness: After rinsing, squeeze a small bundle of fiber firmly and taste a drop of the expelled water (or test with pH-sensitive plant dye if available). Neutral or only very slightly alkaline is acceptable. If strongly alkaline taste or strong slipperiness persists, continue rinsing.

Reuse cooking liquor: The spent cooking liquor contains dissolved lignin and organic compounds but still has significant alkali content. It can be reused for a second batch of cooking (it will be weaker, requiring slightly longer cooking time) or spread on agricultural soil as a potassium fertilizer after diluting with additional water.

Troubleshooting

Fiber cooking unevenly (some parts soft, others still stiff): Insufficient stirring, or fiber packed too densely without enough liquid. Break up dense packs, add more liquid, and continue cooking.

Fiber turns brown or dark during cooking: Common with high-lignin materials — the dissolved lignin discolors the cooking liquor, which stains light-colored fiber. Not always a problem for natural-colored paper. If white paper is required, try a secondary cooking in fresh lye after rinsing, or expose rinsed fiber to sunlight while damp — UV bleaching will lighten discolored fiber over several days.

Fiber smells strongly chemical after rinsing: Incomplete rinsing. Continue with more rinse cycles. A faint alkaline smell is acceptable; a strong ammonia or caustic smell indicates significant alkali still present.

Fiber disintegrates into paste rather than separating into fibers: Over-cooked, especially with too-strong lye. The cellulose itself has been partially degraded. This fiber will produce very weak paper. If some long fibers remain (test by pulling gently — do any stretch before breaking?), proceed to beating with a very light approach. If completely degraded, the material is useful as a fiber supplement blended with stronger fiber, or discard and cook the next batch more carefully.

Nothing seems to dissolve the binding material: Lye too weak. Increase lye strength by recirculating the leachate through the ash bed additional times, or by adding more ash. Test again before beginning the next cook.

Soaking and cooking are the chemical foundation of papermaking. Get this step right and everything that follows — beating, forming, pressing, drying — works easily. Shortcut it and you fight the fiber at every subsequent stage.