Abstract
Unfiltered beer systems retain more proteins, polyphenols, yeast particles, and colloidal material, making haze stability closely dependent on malt protein solubility. This study investigates the relationship between malt protein solubility and haze stability in unfiltered beer systems. Brewing trials were conducted with malts showing different soluble protein levels and modification characteristics. Soluble nitrogen, high-molecular-weight protein fractions, polyphenol binding activity, turbidity, chill haze intensity, foam stability, pH, colour, and storage stability were evaluated. The results show that moderate protein solubility supported foam retention and stable natural haze, while excessive soluble protein increased haze instability during cold storage. High-molecular-weight proteins formed stronger complexes with polyphenols, increasing turbidity variation over time. Low solubility reduced colloidal load but weakened body and foam quality. The study demonstrates that haze stability in unfiltered beer depends on balancing malt protein solubility with polyphenol content and storage conditions. Proper malt selection improves visual consistency and product stability.