Effect of Soaking Step on Tempeh Quality: A Narrative Review

Abstract

Tempeh is a traditional Indonesian fermented food in which soaking plays an important role in determining fermentation performance and final product quality. Previous studies have reported varied effects of soaking duration and soaking media on the chemical, microbiological, physical, and sensory characteristics of tempeh. This study aimed to synthesize published evidence on the effects of soaking on tempeh quality. A descriptive meta-synthesis was conducted using a Systematic Literature Review approach following the PRISMA 2020 guideline. Twenty research articles published in national and international journals were identified and synthesized descriptively according to soaking media, soaking duration, raw materials, and tempeh quality parameters. The synthesis indicates that an optimal soaking duration improves hydration, lowers pH, promotes amino acid formation, and reduces antinutritional compounds, thereby supporting Rhizopus spp. growth during fermentation. Soaking media containing organic acids, including pineapple peel extract, bilimbi juice, vinegar, and lactic acid bacteria, generally promoted faster fermentation and better tempeh quality than water soaking. Overall, optimization of soaking duration and soaking media is a promising strategy for improving tempeh quality and supporting more efficient and consistent production.