Beer fermenting and dry hopping under pressure
- Jan 22, 2022
- 180
- tiantai
Fermenting and dry hopping under pressure has the potential to reduce ester production, flexibility to ferment at higher temperatures, and ability to trap dry hop oil compounds from being removed by carbon dioxide production.
Continuing to work backwards with the studies on the issue, in 1984 it was again found that beer in unagitated ferments under 28 psi (immediately pumped to pressure after filling the fermenter) had slowed ethanol production, reduced final concentration of fusel oils, reduced yeast growth and increased final pH. They also found a distinct increase in the speed of fermentation (so did the Landaud study). Interestingly, they also found that the beer’s fermenting under pressure had less yeast cells in suspension during fermentation, which they attributed to slow absorption of the vicinal diketones towards the end of fermentation in the pressure fermented beers.4 The increase in the beer’s final pH found in this study is interesting as previous research has shown that higher pH in hoppy/bitter beers can result in an increase in bitterness perception. Less yeast cells in suspension is also interesting, I’m curious how fermenting and dry hopping under pressure will impact the clarity and taste of a New England style IPA with research suggesting that more yeast cells in suspension could result in more hop oils in the finished beer.
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Volatile compounds deriving from hop oils face an uphill battle throughout the brewing process when trying to make it into the final beer. Many compounds are evaporated during boiling, some are absorbed during the hot/cold break, some are absorbed by the yeast.14 Other compounds are metabolized through ester hydrolysis and esterification by yeast.17
The downside however to dry hopping early gets to the last point above, that the active fermentation may be striping out these wanted compounds through our airlock! I can attest to this fact, after adding dry hops around 3-5 days into fermentation, I usually come back a few days later to check on things and as soon as I open the fermentation fridge I get hit with a big tropical fruit aromas. So it seems to make sense to experiment with dry hopping under pressure in an attempt to trap or keep the wanted hop compounds contained in the fermentation vessel rather than allowing them to escape.
Aroma differences between the two beers are fairly drastic the pressure fermented beer has distinct orange juice/peel aroma with and floral characteristic that almost borders a little centennial like. Overall the pressure fermented beer aroma is more subdued in terms of intensity and fades rather quickly. The cooler London Ale III beer is extremely inviting (and big time apparent) with more of a soft sweet overly ripe fruit character of strawberries and raspberries with a bit of peach that all comes together to resemble a handful of sweet jelly beans. The flavor of the pressure fermented beer is lacking, overall it’s kind of boring. Maybe this lack of flavor is in part due to the high final beer pH of the pressure ferment (I couldn’t find any research to explain this).
Overall, there is no question I prefer the cooler fermented London Ale III beer with no top pressure, but for a beer that fermented near 80 degrees with a yeast strain that (for me at least) usually produces noticeable esters, I’m intrigued by the process! The higher final beer pH, thicker mouthfeel, low alcohols and esters despite the fermentation temperature definitely seem to have potential depending on what your intended results are. I’m anxious to try a combination of a cool non-pressure ferment with capping of the fermenter immediately after adding the first dose of dry hop in a future hop forward beer.
Benefits of Fermenting Under Pressure
A 2001 study tested the influence of temperature and top pressure and the production of kinetics of biomass, higher alcohols and corresponding esters. In the experiments, aerated wort was transferred into stainless fermenters with the combination of two temperatures 50ºF and 60ºF and two top pressures of 15 psi and 26 psi (converted from bars). Landaud ultimately concluded that temperature had an accelerating effect on fermentation and dissolved carbon dioxide (increased top pressure) resulted decreased yeast and ester production rates likely by affecting the acetyl CoA production rate. In terms of fermentation time periods, the ester production rate increased slowly during the first hours and then fast at maximum fermentation rate. At the higher end of fermentation temperature (60ºF) no lag time was observed for yeast growth.Continuing to work backwards with the studies on the issue, in 1984 it was again found that beer in unagitated ferments under 28 psi (immediately pumped to pressure after filling the fermenter) had slowed ethanol production, reduced final concentration of fusel oils, reduced yeast growth and increased final pH. They also found a distinct increase in the speed of fermentation (so did the Landaud study). Interestingly, they also found that the beer’s fermenting under pressure had less yeast cells in suspension during fermentation, which they attributed to slow absorption of the vicinal diketones towards the end of fermentation in the pressure fermented beers.4 The increase in the beer’s final pH found in this study is interesting as previous research has shown that higher pH in hoppy/bitter beers can result in an increase in bitterness perception. Less yeast cells in suspension is also interesting, I’m curious how fermenting and dry hopping under pressure will impact the clarity and taste of a New England style IPA with research suggesting that more yeast cells in suspension could result in more hop oils in the finished beer.
Dry Hopping Under Pressure
Some of the great NEIPA breweries are rumored to dry hop their beers under pressure, as the tweet below implies. This is likely because volatile compounds deriving from hop oils face an uphill battle throughout the brewing process when trying to make it into the final beer. Many compounds are evaporated during boiling, some are absorbed during the hot/cold break, some are absorbed by the yeast.10 Other compounds are metabolized through ester hydrolysis and esterification by yeast.13Volatile compounds deriving from hop oils face an uphill battle throughout the brewing process when trying to make it into the final beer. Many compounds are evaporated during boiling, some are absorbed during the hot/cold break, some are absorbed by the yeast.14 Other compounds are metabolized through ester hydrolysis and esterification by yeast.17
The downside however to dry hopping early gets to the last point above, that the active fermentation may be striping out these wanted compounds through our airlock! I can attest to this fact, after adding dry hops around 3-5 days into fermentation, I usually come back a few days later to check on things and as soon as I open the fermentation fridge I get hit with a big tropical fruit aromas. So it seems to make sense to experiment with dry hopping under pressure in an attempt to trap or keep the wanted hop compounds contained in the fermentation vessel rather than allowing them to escape.
Aroma differences between the two beers are fairly drastic the pressure fermented beer has distinct orange juice/peel aroma with and floral characteristic that almost borders a little centennial like. Overall the pressure fermented beer aroma is more subdued in terms of intensity and fades rather quickly. The cooler London Ale III beer is extremely inviting (and big time apparent) with more of a soft sweet overly ripe fruit character of strawberries and raspberries with a bit of peach that all comes together to resemble a handful of sweet jelly beans. The flavor of the pressure fermented beer is lacking, overall it’s kind of boring. Maybe this lack of flavor is in part due to the high final beer pH of the pressure ferment (I couldn’t find any research to explain this).
Overall, there is no question I prefer the cooler fermented London Ale III beer with no top pressure, but for a beer that fermented near 80 degrees with a yeast strain that (for me at least) usually produces noticeable esters, I’m intrigued by the process! The higher final beer pH, thicker mouthfeel, low alcohols and esters despite the fermentation temperature definitely seem to have potential depending on what your intended results are. I’m anxious to try a combination of a cool non-pressure ferment with capping of the fermenter immediately after adding the first dose of dry hop in a future hop forward beer.
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