Dip Hopping Contact Time

Much of what is known about dip hopping comes from the brewers at Kirin Brewing who developed the method. The method adds hop pellets before fermentation where the hop matter remains in contact with beer over the course of fermentation. Kirin does not provide details beyond that, but we can make some educated guesses about the process following hop addition.

Most commercially brewed beers these days, whether fermented using lager or ale yeast, typically finish fermenting within a week and are quickly chilled after a short diacetyl rest. Dip hopping, although predominately used by craft brewers for ales, was developed by this famous lager brewery at their Spring Valley Brewery in Tokyo, Japan, on the grounds of the original Kirin Brewery built in 1869. Today, the Spring Valley Brewery serves as a playground for Kirin’s innovative brewing team with multiple locations.

Spring Valley’s Toyojun 496 India Pale Lager is the brewery’s flagship beer and the one that introduced the dip hopping method. According to Kirin’s website, “Spring Valley Toyojun 496 uses the ‘dip hop method,’ in which hops are steeped in the beer for seven days. By carefully and thoroughly extracting the aroma from hops, also known as the ‘soul of beer,’ we have achieved both a rich aroma and a smooth aftertaste, resulting in the beer’s characteristic rich flavor and clean aftertaste.”

Grassy hop characters can be caused by several factors, including hopping rate, beer pH, and hop quality. I have not included time in this list because research related to extraction rate of hop compounds from pellet hops conducted by Peter Wolfe, a PhD student at the time in Tom Shellhammer’s group at Oregon State University, showed that hop pellets quickly give up their goods when added to beer. In any case, dip-hopped beers do remain in contact with hops during fermentation and grassy characters are not found in 496. The typical practice these days is to either rack beer from the fermenter into a lagering vessel after fermentation or to remove yeast and hop sediment from the cone of unitank fermentation vessels following cooling.

Your question about aroma losses during fermentation has been specifically addressed in several studies conducted by Kirin. Interestingly, hop pellets act as carbon dioxide nucleation sites and reduce the concentration of dissolved carbon dioxide in beer during fermentation, leading to scrubbing of undesirable volatiles. Data from beers brewed with and without dip hopping show less of the sulfur-
containing, onion-like compound 2-mercapto-3-methyl-1-butanol (2M3MB) and less myrcene, a hop terpene known for earthy, musky, and dank aromas, with dip hopping. The same study shows the retention of linalool, with its pleasantly fruity and floral aromas, to be similar when beers are either dry hopped or dip hopped.

I recently visited Japan on a business trip and did learn something new about dip hopping. I have speculated in the past that this method was developed by innovative brewers simply experimenting with different ways to use hops. It turns out that Japanese tax law is the real reason behind dip hopping. Happoshu is a category of beer and beer-like beverages defined by ingredients and processes used for production. Beers brewed with less than 67% malt are classified as happoshu. Because the tax rate on happoshu is less than beer, some breweries developed happoshus brewed with very little malt to serve the low-cost market. Changes to the tax code have recently closed the tax rate difference between beer and happoshu and brewers are using more malt in their beers. Malt usage, however, is not the only thing distinguishing happoshu from beer. A beverage is also classified as happoshu when ingredients are added to beer after yeast pitching. This means that many imports from Belgium and the U.S., for example, are classified as happoshu because of dry hopping or fruit additions. To avoid the happoshu classification and consumer biases that come with it, Kirin developed dip hopping, and the rest is history.

Response by Ashton Lewis.