How is soy fiber made?

November 15, 2025 •

4 min read

According to research, the production of soy fiber is a highly sustainable process because it recycles byproducts from tofu and soy milk production. The specific process outlining how is soy fiber made, however, differs significantly based on its intended application in either the food or textile industry.

Quick Summary

Soy fiber is created by processing byproducts of soybean food production, with different methods used depending on the end goal. For soft, regenerative textile fibers, a protein-rich solution undergoes a wet spinning process, while for food applications, dietary fiber is extracted from okara using enzymatic or chemical treatments.

Key Points

Two Primary Types: Soy fiber is made into either regenerated protein fiber for textiles or dietary fiber for food products.
Source Material: The main raw material for both types of soy fiber is the leftover soybean residue, known as okara, from the production of soymilk and tofu.
Textile Fiber Process: Soy protein fiber is manufactured via a wet spinning process, which involves extracting protein and extruding it into filaments.
Dietary Fiber Methods: Food-grade soy fiber is extracted from okara using methods such as enzymatic hydrolysis or alternating ultrasonic and alkaline treatments.
Dual Functionality: The different production methods enable soy fiber to serve distinct purposes, from creating soft, luxurious fabrics to acting as a binder and emulsifier in food products.
Sustainability: Producing soy fiber from a food byproduct helps reduce waste and increase the value derived from soybeans.

The manufacturing of soy fiber is an excellent example of maximizing resource utilization within the food industry. By taking the leftover pulp, or okara, from products like tofu and soymilk, companies can extract and refine valuable fiber. However, the path taken from raw byproduct to finished soy fiber is not singular; it follows distinct routes for creating either luxurious textiles or functional food additives.

Production of Soy Protein Fiber (Soy Silk)

This process leverages the protein content within the soybean residue to create a man-made fiber known for its softness and drape, often referred to as 'soy silk'. The method, called wet spinning, transforms the protein into long, continuous filaments.

Step-by-Step Wet Spinning Process

Oil Extraction: The process begins with thoroughly cleaning and dehulling the soybeans. The beans are then treated with a solvent, such as hexane, to remove the oil, leaving behind a high-protein, oil-free meal.
Protein Extraction: The oil-free soybean meal is steeped in a dilute alkaline solution, like sodium hydroxide, to dissolve the protein. This creates a protein-rich liquid.
Protein Precipitation: An acid, typically sulfuric acid, is added to the solution to bring the pH down to the isoelectric point of soy protein (around 4.5). This causes the protein to precipitate out of the solution, forming a creamy-white powder.
Spinning Solution Preparation: The extracted protein powder is dissolved in another alkaline solution, filtered, and deaerated to remove impurities and air bubbles. The solution is then aged to achieve the proper viscosity for spinning.
Fiber Formation (Wet Spinning): The viscous protein solution is forced through a spinneret, which is like a showerhead with many tiny holes. The spinneret is submerged in a coagulation bath, typically an acid solution with salts. As the solution hits the bath, it solidifies into fine filaments.
After-Treatments: The newly formed filaments are washed, stretched (a process known as drawing to enhance strength), and treated with finishing agents. They are then dried and cut to the desired length.

Extraction of Soy Dietary Fiber

This method focuses on obtaining the cellulose, hemicellulose, and pectin from the soybean cell wall, producing a product widely used in the food industry for its functional properties.

Methods for Food-Grade Fiber

Enzymatic Extraction: Enzymes, particularly cellulase, are used to break down the complex structure of the soy residue (okara), releasing both soluble and insoluble dietary fibers. This method is praised for its efficiency and ability to increase the proportion of soluble fiber.
Alkaline/Ultrasonic Treatment: An innovative method involves using alternating ultrasonic and alkaline treatments on okara. This process creates a porous structure within the fiber, improving its water-holding and oil-binding capacities.
Chemical Retting: This process uses an alkaline solution, like sodium hydroxide, at high temperatures to dissolve components like pectin, lignin, and hemicellulose, thereby isolating the desired fiber components. Subsequent steps involve neutralizing and purifying the extracted fibers.
Low-Temperature Continuous Phase Transition Extraction: A novel approach that uses a solvent like n-butane at low temperatures and controlled pressure to efficiently extract high-purity insoluble dietary fiber from soy sauce residues.

Comparison of Soy Protein and Dietary Fiber Processes

This table highlights the key differences between the manufacturing processes for the two main types of soy fiber.


Feature	Soy Protein Fiber (Textile)	Soy Dietary Fiber (Food)
Primary Source	Oil-free soy meal	Soybean residue (okara) or hulls
Extraction Method	Alkaline extraction, followed by acid precipitation	Enzymatic, ultrasonic, or chemical treatments
Key Component	Regenerated protein	Complex matrix of insoluble and soluble fiber
Final Shaping	Wet spinning into filaments	Drying and milling into powder
Primary Use Case	Clothing, bedding, upholstery	Food additive, stabilizer, binder

Applications of Soy Fiber

In the food industry: Soy dietary fiber acts as a binder, emulsifier, thickener, and stabilizer in a wide range of products including bakery goods, meat products (like sausages and burgers), and sauces. It helps retain moisture and improve texture. For more on food applications, see this review on soy protein and fiber's nutritional benefits.
In the textile industry: Known as 'soy silk,' the protein fiber can be spun into soft, lightweight yarns. It is used to make clothing such as shirts, sweaters, and underwear, and can be blended with other fibers like cotton or silk for enhanced properties.

Conclusion

Understanding how is soy fiber made reveals an innovative use of agricultural byproducts that benefits both the food and textile industries. The process diverges depending on the desired end-product, with wet spinning used to create regenerated protein fiber for textiles and various chemical or enzymatic methods employed for extracting dietary fiber for food applications. This dual functionality underscores soy's versatility and its role in creating sustainable and value-added products from what was once considered waste.

Frequently Asked Questions

The main byproduct is soybean residue, or okara, which is the pulp left over from processing soybeans into products like tofu and soy milk.

Soy protein is extracted from oil-free soybean meal by steeping it in a dilute alkaline solution. This is followed by acid precipitation to isolate the protein.

No, they are different. Food-grade soy fiber is extracted to get dietary fiber from the plant's cell walls, while textile-grade soy fiber is a regenerated protein fiber produced through a wet spinning process.

Wet spinning is a process where a viscous solution, in this case of soy protein, is extruded through tiny holes into a chemical bath. This causes the solution to coagulate and solidify into continuous filaments.

In food, soy dietary fiber acts as a stabilizer, thickener, and emulsifier. It has high water-binding capacity, which improves texture and moisture retention in products like baked goods and meat.

Modern techniques for extracting dietary fiber include enzymatic extraction using enzymes like cellulase and a method involving alternating ultrasonic and alkaline treatments.

The process is sustainable because it repurposes a major byproduct of the soybean processing industry (okara) that would otherwise be discarded as waste, creating valuable new products.