Multi-Response Desirability Optimisation of Sucrose Charge in Black-Tea Kombucha: Ethanol, Acetic Acid, and Biocellulose as Critical Quality Attributes

Eki Noor Istiqomah (Master's Program in Pharmacy, Faculty of Pharmacy, Universitas Sanata Dharma, Yogyakarta, Indonesia)
Sri Hartati Yuliani (Master's Program in Pharmacy, Faculty of Pharmacy, Universitas Sanata Dharma, Yogyakarta, Indonesia)

Natural Sciences Engineering and Technology Journal
Vol. 6 No. 1 (2026): Natural Sciences Engineering and Technology Journal

Kombucha is a functional beverage produced by a symbiotic consortium of acetic acid bacteria and osmotolerant yeasts, and its commercial acceptability depends on a narrow compliance window in which residual ethanol must remain below 0.50% w/v while organic acidity is sufficient for flavour and microbial safety. The initial sucrose charge is the single manipulable process parameter that governs both outcomes, yet it is rarely treated as a formally optimised critical process parameter. Four sucrose charges (5, 10, 15 and 20% w/v) were evaluated in black-tea kombucha fermented statically for 14 days at 25–28 °C with a standardised 50 g pellicle and 10% v/v starter, three vessels per level. Composites were assayed in analytical triplicate by GC-FID (ethanol), ion-exclusion HPLC (acetic acid), potentiometry (pH) and alkalimetry (titratable acidity), with calliper measurement of pellicle thickness. Data were analysed by one-way ANOVA with Shapiro–Wilk, Levene and lack-of-fit diagnostics, Tukey's HSD, polynomial response modelling and Derringer–Suich desirability optimisation. Sucrose charge affected every attribute (all p < 0.001; η² = 0.685–0.998). Ethanol was biphasic, peaking at 0.341 ± 0.007% w/v (95% CI 0.324–0.359) at 10% sucrose — only 68% of the compliance threshold — whereas acetic acid fell monotonically and the acetification index collapsed 9.9-fold from 5% to 20% sucrose. Pellicle thickness increased strictly linearly (R² = 0.974). Composite desirability identified 19.1% w/v as the predicted optimum within a 15–20% w/v design space, with 15% preferred when ethanol headroom is prioritised. Sucrose charge is a tractable, instrument-free control lever for halal-compliant kombucha manufacture.