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Hops
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More recent studies have shown that there is a difference in this enzymatic power between different hop varieties. [https://www.asbcnet.org/publications/journal/vol/2017/Pages/ASBCJ-2017-2257-01.aspx Cibaka et al. (2017)] reported an increase in ABV when dry hopping with Amarillo and Sorachi Ace hops, but not when dry hopping with Citra or Hallertau Blanc. Interestingly, they also found that Mosaic hops resulted in the opposite effect and it was hypothesized that Mosaic hops might release some sort of unidentified molecule that inhibits yeast fermentation/growth or viability <ref name="Kirkendall_2018" />.
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) are relatively stable. Further work needs to be done to identify the enzyme that is responsible for dry hop creep <ref name="Kirkendall_2018" />.
===Aged Hops in Lambic===