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Hops
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Dry hopping can contribute to bitterness in beer through oxidized alpha acids and oxidized beta acids. Some alpha acids will also dissolve into the beer, which are estimated as being 10% as bitter as iso-alpha acids. Dry hopping also has a linear impact on the pH of beer regardless of the starting IBU or pH: the pH rises by 0.14 per pound of hop pellets per barrel of beer in a beer that started with a pH of 4.2 (~0.5 ounces per gallon) <ref name="Maye_2016" /><ref name="Shellhammer, Vollmer and Sharp, CBC 2015"/>. This rise in pH might be less in more acidic beers that are dry hopped since pH is a logarithmic scale. Dry hopping can also reduce head retention in beers, although this is variety dependent (one study found that dry hopping with Eureka and Apollo hops increased head retention, while dry hopping with Bravo, Centennial, and Cascade decreased head retention). Extended dry hopping times (after 3 days) can also reduce head retention <ref name="Maye_EBC2017" />.
Although the mechanisms are not fully understood, dry hopping inhibits ''Lactobacillus''. Humulinic acids have been found to greatly inhibit bacteria (see [[Hops#Antimicrobial_Properties|Antimicrobial Properties]]). Other compounds such as non-isomerized alpha acids, other acids, or the small amount of isomerization of alpha acids that happens in beer at room temperature <ref>[http://scottjanish.com/zero-hot-side-hopped-neipa-hplc-testing-sensory-bitterness/ Janish, Scott. "Zero Hot-Side Hopped NEIPA | HPLC Testing for Sensory Bitterness". ScottJanish.com. Retrieved 03/09/2017.]</ref>, could contribute to inhibiting lactic acid bacteria. See the links below.
* [https://www.facebook.com/groups/MilkTheFunk/permalink/1416506428377567/?comment_id=1458425540852322&comment_tracking=%7B%22tn%22%3A%22R%22%7D Caroline Whalen Taggart's data point on the effects of dry hopping on ''L. plantarum'' (GoodBelly). No hops finalized at a pH of 3.53, and the dry hopped version finalized at a pH of 4.35.] She used around 4 grams per gallon of 10-15 AA hops <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1746176672077206/?comment_id=1746211618740378&comment_tracking=%7B%22tn%22%3A%22R0%22%7D Carloine Whalen Taggart. Milk The Funk Facebook group. 07/06/2017.]</ref>.