The New IPA: Chapter 7

 I'm reading a few chapters ahead of my reports, so today is catch up day. Dry Hopping is the topic at hand in this chapter. Coincidentally, I recently read some of Ronald Pattinson's Shut Up About Barclay Perkins. Other than documenting travel to Chicago and Bamberg, he records Rose's 1896 dry hopping regimen. So no, dry hopping is not a new development. 

Oxygen can corrupt a beer. Dry hopping introduces oxygen to the wort. In order to put this oxygen to use, dry hop during early fermentation. The yeast will use the oxygen before it can oxidize the wort. How else can you avoid oxygen?

1. Add hops to an empty keg/brite and purge the tank. Then transfer into the tank while releasing pressure from the receiving tank. Use a spunding valve to ensure a steady pressure release from that receiving tank. 
2. At my brewery, we purge the receiving tank by attaching CO2, filling to 6 PSI, releasing it, filling to 6 PSI, releasing it, and then filling it to 12 PSI. Then we attach CO2 to the fermentation tank, increase the PSI above the receiving tank, and then transfer. As beer transfers out, pressure will drop because there is empty space in the tank, so the CO2 will disperse over more area. John Kimmich of The Alchemist also discusses how CO2 treats beer more gently than a pump. The full discussion can be found here. 
3. We also add CO2 to the headspace when adding dry hops through top ports. This is doable on a corny keg, just add 5-10 PSI when removing the lid for your addition.

The smaller batch size, the more oxidized your beer will be. There is a higher surface area to volume ratio, which means more beer will come in contact to oxygen.

In the discussion linked above, John Kimmich says dry hopping shouldn't exceed 4 days. Here, Janish cites a study by Peter Wolfe which found linalool and myrcene levels drop throughout a week-long dry hop. After 24 hours, these terpenes may reach peak extraction. Extraction time is temperature dependent. Dry hopping in the 33 degree range will take three or four days, but dry hopping at 68 degrees may take 24 hours. 

The larger the vessel, the less efficient the dry hop. Homebrewers also experience faster extraction than production breweries.

Rousing also increases extraction, but increases astringency and bitterness as well. The astringency and bitterness come from a higher polyphenol content in the final solution. Polyphenols may produce a lingering harshness that comes across as metallic. This sensation can also result from a high protein grist. 

Centrifuges are commonplace in modern breweries. Centrifuging a Hazy IPA can reduce the myrcene (green) contents and the polyphenols by half. A more approachable way to reduce astringency and harsh bitterness is to use pre-isomerized iso-alpha-acid products like Tetra. John Kimmich says he uses no hot-side hops, only hop extract in Heady Topper. These extract products create a smooth, diminshing bitterness rather than an off-putting metallic finish. Using extracts on the hot-side will enable a heavy dry hop without heavy humulinone and polyphenol extraction. 

Another option is to dry hop early in fermentation. Polyphenols will interact with yeast and drop out of solution due to flocculation. Lower alpha-acid hops (Cascade!) are prime candidates for this early dry-hopping experiment, because they often have increased polyphenol contents. Generally, as alpha-acid content increases, polyphenol content decreases. 

Selecting low alpha-acid hops to dry hop with may increase extraction. They will swell more than high alpha-acid hops, which creates more surface area for extraction of the hop compounds. Furthermore, dry hop with loose pellets. They will spread over a greater surface area than when they're in a bag. For homebrewers, get a floating dip tube. You can dry-hop loosely without pulling the hops. The only caveat is that you would need to transfer beer before serving it, requiring two vessels per finished batch. 

Spreading out dry-hop charges across two or three sessions may reduce polyphenol extraction and bitterness. Furthermore, each extraction may become more efficient. 

Janish recommends starting with a small dose of hops on the homebrew scale. Too high of a dose may evoke the hops' herbal and tea-like characteristics. 

Compounds other than total oil percentage, such as Geraniol and Beta-Pinene are good indicators of a hops' aroma quality and intensity. Geraniol can be biotransformed into citronellol, which is a lemon-lime like compound. But when combined with the total oxygen fraction of a hop, the total oil percentage can be an indicator of fruity monoterpene alcohols.

Filtration removes woody, spicy, and resinous characteristics. Monoterpene alcohols tend to last through the process. 

Head retention mostly results from a healthy grist. But an acid found in hops called dihydroisohumulone can also improve foam stability and lacing. 0-15 IBUs and 35+ IBUs are sweet spots when focusing on foam stability. High pH detracts from foam (dry-hopping increases pH). Alpha-acids also create good foam. Dry-hopping at cold temperatures is a good way to introduce foam positive acids to your beer. Hop extracts can also increase foam stability. Undermodified malts can also retain 30% more foam enhancing proteins than typical modified malts. This explains why decoction-mashed beers strike me as having high head retention! Schilling and Bierstadt lagers come to mind.

Malt modification is indicated via the Kolbach index percentage. A 39.9% KIP malt produced better foam than a 43.7% malt. Chit malt is a favorite of Janish, and he brings it up again as it's intentionally under-modified. Even a utilization of 10% chit malt can increase beer foam when compared to a recipe with standard 2 row.

If you've made it this far, congratulations. You deserve a fuggin beer. This was a dense one. I'm gonna continue on, placing this chapters findings into my IPA recipes. Cheers mate.