This post continues our series on natural dyeing techniques.
Today, we will introduce a method that is frequently inquired about during our workshops — the “Soy Milk Processing” (豆汁処理, Gojiru) method. If you’re having trouble achieving a deep, rich color when dyeing, this method might help.

What is Soy Milk (Gojiru)?

The History of Soy Milk

Soy milk refers to the liquid obtained by soaking soybeans in water and then straining them. Soy milk is an essential material in natural dyeing, and its use in pre-dyeing (under-dyeing) techniques has been practiced in Japan for a long time.Soy milk contains a high amount of plant-based proteins, making it effective in helping to fix and set colors, coat colors, prevent bleeding, and protect the starches used in dyeing. For example, in Ryukyu Bingata, a traditional Okinawan dyeing technique, soy milk is mixed with pigments and rubbed into fabric to help the color adhere. Soy milk is also used in indigo dyeing for pre-dyeing processes.In Japanese painting, “Nikawa” (animal-based collagen) is often used for preventing bleeding and coating colors, and soy milk, being another type of protein, serves a similar purpose in natural dyeing.

Why Soy Milk Helps Achieve Darker Colors

Proteins, when broken down, become peptides or amino acids, both of which are cations (positively charged ions). On the other hand, natural dyes from plants often contain anionic (negatively charged) compounds. This creates a magnetic-like attraction between the protein in soy milk and the plant-based dye, which helps the dye to bond more strongly to the fabric, resulting in a richer color. In simple terms, proteins help attract and hold the natural dyes, which is why the fabric ends up dyed more deeply.

Materials Suitable for Soy Milk Processing

Soy milk processing works best with plant-based fabrics such as cotton or linen. Animal-based fibers like silk and wool, which are already made of protein, can be dyed without the need for soy milk treatment.

Materials Needed

Before beginning the dyeing process, prepare the following materials and tools:

Fabric to be dyed

The fabric or thread you want to dye deeply
(for this example, we are using 120g of sashiko thread, and no animal fibers are needed).

Materials

Soybeans
(for this example, 36g of soybeans, about 30% of the weight of the fabric).

Tools

Kitchen scale　Blender　Bowl or bucket　Straining cloth　Lukewarm water (50°C)

How to Perform Soy Milk Processing

Here is the step-by-step process for soy milk processing using dried soybeans. You can substitute with store-bought soy milk starting from step 4 if needed.

1. Measure the fabric and soybeans

Weigh the fabric first, and then prepare 30% of the weight in soybeans.
For example: If the fabric weighs 120g, you will need 36g of soybeans (120g x 0.30 = 36g).

2. Soak the soybeans

Place the measured soybeans into a container and add water.

Cover with plastic wrap or a lid and store them in the refrigerator for at least 12 hours.

Once the soybeans swell to about 2-3 times their original size, they are ready for the next step. Their weight will increase by about 4 times during soaking.

3. Make soy milk using a blender

After soaking the soybeans for more than 12 hours, place them into a blender. Add lukewarm water (50°C) at a ratio of 20 times the amount of dried soybeans.

For example, 36g of dried soybeans would need 720cc of lukewarm water. Blend well for about 30-60 seconds.
Once blended, pour the mixture into a bowl covered with a straining cloth. Squeeze out the soy milk well. The residue left in the cloth (called “okara”) can be used for food, so don’t discard it.

Now you have freshly made soy milk!

4. Soy Milk Processing

Submerge the fabric into the soy milk mixture.

Gently massage the fabric in the liquid for 2-3 minutes to ensure that the soy milk is fully absorbed by the fabric.

After the fabric is fully soaked, wring it out well and hang it to dry.

Store any leftover soy milk in the refrigerator, covered with plastic wrap.

You can reuse it later for another batch.

5. Repeat steps 4 once or twice

To prevent uneven dyeing, it’s recommended to repeat step 4 one or two more times. If using leftover soy milk, warm it up in the microwave before reusing it.

6. Completion

At this point, the fabric will have a deeper color. It may feel a bit stiffer than usual, but once it is dyed, it will soften.
After processing, allow the fabric to dry completely. Once dry, store it in a plastic bag (such as a Ziploc bag) in a cool, dry place, away from humidity. Ideally, use the fabric within six months.

Final Thoughts

Soy milk is a versatile and essential material for natural dyeing. If you’re unsure, it’s a good idea to start with soy milk as a pre-dye treatment. Unlike other treatments that may affect the color tones, soy milk is gentle and reliable. Plus, it is a natural material, making it environmentally friendly and safe for humans as well.

For thick fabrics or three-dimensional items, be sure to massage the fabric well and repeat the soy milk processing at least twice to avoid uneven dyeing.

Maito Design Works Maito Komuro

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