The Impact of Whirlpool Hop Addition on the Wort Metal Ion Composition and on the Flavor Stability of American Style Pale Ales Using Citra® Hop Extract and Pellets

The characteristic hoppy flavor of pale ales is known to be unstable and deteriorates during the beer's shelf life. Metal ions, in particular iron and copper, have a prooxidative effect and therefore accelerate beer flavor deterioration. Recent studies suggest that hop constituents may complex metal ions in beer thereby suppressing their negative effect on beer flavor stability. Using benchtop wort boiling experiments and quantitating metal ions in the cast wort, this study determined that different whirlpool additions of up to 3.0 g/L hop extract or up to 17.4 g/L pellets significantly reduced metal ion concentrations in wort, especially Fe, which was reduced by a factor of up to 6 compared to the control. Based on identified dose- and product-related effects, 2.5-hL brewing trials were performed using a selection of whirlpool hopping levels with either extract or pellets revealing significant differences in resinous and sweaty flavor. The flavor of the beer hopped with 5.8 g/L pellets was perceived as 8 times more resinous and 9 times sweatier than the control revealing clear differences between extract and pellets, especially at the lower hopping levels. The beer flavor stability was predicted using ESR spectroscopy and verified by performing forced aging experiments at 30 degrees C and monitoring beer flavor changes by sensory evaluation. Results indicate that both extract and pellet whirlpool hopping improve beer flavor stability by reducing the formation of age-related off-flavors and by supporting the retention of flavors related to freshness with only minor variations between the two hop products.