AbstractBACKGROUNDArabinoxylans (AXs) are partially water‐extractable polymers that cause problems of viscosity and filterability during beer brewing. This study investigated the effects of Kolbach index (KI) on water‐extractable AXs (WEAXs).RESULTSKI had positive correlations with extract (r = 0.845) and free amino nitrogen (FAN) (r = 0.958). The contents of malt WEAXs (WEAXsm), total AXs and wort AXs (WAXs) were 10.8–11.6 g kg−1, 57.5–60.8 g kg−1 and 137.5–140.5 mg per 100 mL respectively and the corresponding arabinose/xylose (A/X) ratios were 0.52–0.56, 0.55–0.62 and 0.48–0.50. The molecular weight (Mw) ranged from 4.92 × 104 to 6.93 × 104 Da for WEAXsm and from 1.24 × 104 to 2.90 × 104 Da for WAXs. KI had negative correlations with the average degree of polymerization (avDP) of malt (r = −0.877) and wort (r = −0.978). Wort viscosity showed a positive correlation with the Mw of WEAXsm (Mwm) (r = 0.821).CONCLUSIONIncreasing KI can promote the degradation of the xylan backbone, while it cannot affect the branching of the polymer chain and the content and Mw of WEAXs. © 2014 Society of Chemical Industry