Samenvatting

This thesis explores the feasibility of valorising okara, a by-product from tofu and soy milk production, through tempeh fermentation. The topic was initiated from the potential value of okara as a fibre-rich material, especially regarding the possible effect of fermentation on its soluble and insoluble fibre profile. However, the main focus of this study is not full nutritional characterisation, but the development of a feasible preliminary process approach for okara-based tempeh production.

The study shows that moisture control is the most critical factor influencing fermentation performance. Experimental observations demonstrated that successful mold growth and cake formation depend not only on total moisture content, but also on how water is distributed within the substrate, particularly whether excess free water is present. Based on the trials, a moisture range of approximately 40–50% was identified as the most suitable process window. Within this range, the substrate provided enough water for Rhizopus spp. growth and cake formation while limiting free water, soft texture, microbial instability, and visible spoilage risk.

As mentioned above, the findings also show that the method used to control moisture is important. Rehydrated dried okara was less successful because the added water did not appear to restore a suitable substrate structure and was more likely to behave as free water. In contrast, partially dried fresh okara showed better fermentation performance, suggesting that controlled drying of fresh okara is a more feasible approach for future process development.

In this way, the thesis contributes both to research and development. From a research perspective, it identifies moisture behaviour and free water control as key factors affecting okara fermentation. From a development perspective, it defines preliminary process requirements for producing a stable okara-based tempeh product. These findings provide a practical foundation for future optimisation, including further work on process standardisation, product safety, and fibre changes during fermentation.