Impact of microbiome on malt quality indices in barley: insights from systematic review and meta-analysis

Barley ( Hordeum vulgare ) is a primary raw material for malt production, and microbial dynamics during steeping, germination, and kilning significantly influence malt quality and safety. However, scattered results across individual studies limit a unified understanding. This systematic review and meta-analysis aimed to evaluate the role of microbial diversity in shaping the chemical, enzymatic, structural, and functional attributes of malt, with an emphasis on beneficial and harmful microbial taxa. A comprehensive search was conducted across PubMed, Scopus, Web of Science, ScienceDirect, and Google Scholar (from January 1990 to October 2025). Twenty-six studies reporting quantitative outcomes were included. All meta-analysis analyses were conducted using the 'meta' package of R statistical software (version 4.4.1). Effect sizes were pooled for major quality indices including diastatic power (DP), free amino nitrogen (FAN), Kolbach index (KI), protein content, β-glucan, viscosity, extract yield, wort pH, wort color (measured in European Brewery Convention [EBC] units, reflecting light absorption and beer color intensity), and fermentability. Lactic acid bacteria (LAB), particularly Lactiplantibacillus plantarum and Lactiplantibacillus brevis , significantly improved diastatic power (DP, °WK) (effect size = 1.184, 95% confidence interval (CI): 1.045–1.323, P < 0.001), β-glucan concentration (mg/L) (effect size = 1.158, 95% CI: 1.035–1.281, P = 0.010), and moisture content (%) (effect size = 1.514, 95% CI: 1.172–1.856, P = 0.001). Yeasts such as Saccharomyces cerevisiae improved fermentability and free sugars, although their effects were strain-dependent. Filamentous fungi, particularly Fusarium culmorum , increased β-glucan and generated mycotoxins, negatively affecting malt quality and safety. Heterogeneity (I² > 80%) reflected geographical and methodological variation. LAB represent promising biocontrol agents that improve enzymatic and structural quality of malt, while Fusarium remains a major safety threat. Strategic microbiome management and the use of advanced technologies such as next-generation sequencing (NGS) will be critical for enhancing malt quality under variable environmental conditions.