Polymer composites have been formed by mixing component materials in extruders or compression molds. Agricultural biopolymers are usually mixtures of several compounds; however, high-temperature processing can cause unwanted consequences such as decomposition, gas generation, and phase-separation. This report introduces a new technology to form biodegradable polymer composites that can replace existing petroleum-based polymers. With this newly developed process, polymer composites are produced at room temperature. During the process, micrometer-scale raw materials are coated with zein, which has strong adhesive properties, and are then compressed to form a rigid coherent material. Since this technique does not require purification of the raw materials, various types of compounds can be used as component materials. In this report, wheat protein, gluten, was used as a matrix material. The compressive yield strength of the product formed from gluten is ca. 40 MPa, comparable to that of polypropylene.