Changes

Kirkendall et al. (2018) found that hop varieties also have a varying ability to ferment dextrins. They reported the following ABV increases when dry hopped in a pale ale at one pound per barrel: Centennial hops (+0.27%), Citra (+0.12%), Simcoe (+0.33%), Cascade (+0.49%) and Amarillo (+0.49%). Prolonged contact with Centennial hops (42 days) resulted in a nearly 1% increase in ABV. Rousing the hops into suspension hastened the increase in ABV compared to samples that were left still. From their results, it appears as though contact with hops during dry hopping continues the breakdown of starches and dextrins into fermentable sugars. They also concluded that dry hopping at a temperature that is too cold for the yeast strain in the beer to ferment resulted in no change in ABV. They compared the enzymatic activity of Centennial hops that were stored at -20°C versus room temperature storage and found that there was no significant difference, indicating that the as of yet unidentified enzyme(s) enzymes are relatively stable <ref name="Kirkendall_2018" />. Kirkpatrick and Shellhammer (2018) found that the enzymes responsible for the conversion of dextrins into sugars include amyloglucosidase (removes glucose from non-reducing ends of α-1,4 and branching α-1,6 linkages, with a preference for α-1,4 linkages and longer chain oligosaccharides), α-amylase (hydrolyzes randomly along glucopolysaccharides to produce maltose, maltotriose, maltopentaose, and maltohexaose products from amylose as well as maltose, glucose, and branched dextrins from amylopectin), β-amylase (saccharifiying enzyme, cleaving maltose in small amounts from nonreducing ends of glucopolysaccharides, and to a minor extent, maltotriose), and limit dextrinase (debranches limit dextrins at α-1,6 linkages, producing linear α-1,4 chains which can further be degraded by the combined action of amylases). They were able to successfully extract them from Cascade pellet hops using commercially available assays (enzyme specific para-nitrophenyl blocked oligosaccharide substrates). The amount of α and β-amylase found in Cascade hops was well below that of malted barley, but within the range reported in other plant leaves. These enzymes are denatured by high temperatures, and as such would be denatured when boiling hops. They reported a similar increase in ABV of 1.3% after 40 days when dry hopping a beer with Cascade hops (and a decrease of 1.9°P) at a rate of 10 g/L. They also found that the hops contained glucose and a small amount of fructose, which accounted for a sugar increase of 0.02−0.03 °P per gram of hops.