What are polyphenolsPolyphenols are a group of flavor-contributing compounds introduced from grain and hops. Roughly 80% of polyphenols are grain-originated. They contribute flavor, astringency, perception of bitterness, haze, oxidative effects and antioxidative effects. They are not well understood, at least as far as their flavor contributions. Polyphenols tend to be filtered out of beer, especially pale lagers (think industrial light lagers), because they contribute to haze and reduce long term stability. Most polyphenols are oxygen-reactive so their removal before packaging improves the stability and shelf life of beer. They contribute to many of the aged beer flavors, from toffee and caramel flavors to some of the cardboard aroma that can appear in aged beers. Some of those flavors can be valued in aged beers, particularly in big beers like barleywines and imperial stouts. However, not all polyphenols produce pleasant flavors over time.
Not all beers are designed to benefit from the existence of polyphenols in the packaged product. Beers intended to be consumed within months after production generally are designed to remain stable over expected shelf life, rather than develop aged flavors that can come across as stale (especially when poor packaging practices introduces a lot of oxygen and the oxidative reactions result in cardboard and wet paper aromas). Add that some, but not all, polyphenols are precursors to haze and you get another great reason to use filters or other methods to try to remove them from the majority of beer styles. Polyphenols also contribute astringency and the perception of bitterness. At high levels they can add an unpleasant dryness but at moderate levels help add to that bracing bitterness in IPAs and IIPAs. So if you are trying to make beers that are "smooth" or "easy drinking" like BMC-type light lagers you also want to remove that dry mouthfeel.
Interesting research is being performed in how polyphenols affect beer based on storage conditions. Beers that lack polyphenols suffer far greater staling in flavor and aroma when stored at warm temperatures. Beers with polyphenols scored less on taste and aroma panels in cardboard aroma (oxidation) even after six weeks of storage at warm temperatures.
The desire to avoid excessive vegetal matter in the kettle has led to an increasing use of hop extract in brewing, especially for bitterness additions. Research indicates people find the use of pellet hops (the research did not also compare whole flower hops) to produce more pleasant tasting and smelling beer, due to the presence of the polyphenols removed during the extract process. Additionally, the use of pellets when the beer was stored warm--even up to 80F--produced a more stable beer. As an aside, perhaps an extrmely important aside, the same studies found the use of pellet hops with a 90 minute boil developed a harsher bitterness than beers with a shorter boil time. Hop polyphenols, studies suggest, improve flavor stability while malt-based polyphenols tend to produce both desired aged-beer flavors and undesirable stale flavors.
Many of the industrial brewers are developing hop extracts from spent hop material that can be used in subsequent beers that are indistinguishable from actual hops in flavor and aroma. (This subject is discussed in For the Love of Hops.) This leads to interesting opportunities to not only extend the value of hops but also to construct flavor/aroma combinations that do not naturally exist in a hop variety. It also allows brewers to put together combinations of polyphenols that have the flavor and aroma of hops but add greater amounts of stability, improving the shelf life of beer. Maybe someday that will make Stone's Enjoy By series terribly anachronistic. However, the research into this field is still very young.
What polyphenols mean for homebrewersWe're not out there working with a lot of hop extracts, although some homebrewers are using hop extracts for bitterness, but polyphenols appear in our beers just as much as commercial beers. The key takeaway for us is not terribly different from our professional companions: beer packaging, storage and production techniques should reflect our best ability to produce a great product.
- Oxygen pick up should be reduced as much as possible regardless of the packaging method (keg or bottle). Because bottling typically risks greater oxidation than kegging, removal of polyphenols is probably not a great idea for those of us regularly bottling.
- For those of us who cannot keep all our beers cool after carbonation, hop-based hpolyphenol removal should be avoided because it will reduce the stability but in low-hopped beers polyphenol removal may be a good idea.
- Beers intended to be aged can benefit from polyphenol presence so filtering and other polyphenol removal techniques may be detrimental to the aging process. That should be a planned decision during the design process.
- Beers intended to be consumed within months (but more than weeks) may be good candidates for polyphenol removal, especially if they are not hoppy beers, to keep them stable over the course of months.
- The most popular polyphenol removal technique involves the use of PVPP resin, which is not available to homebrewers, but less effective options to filter or fine can have some positive results. One thing that can be detrimental about polyphenol removal that is available to homebrewers is when dry hopping, which adds polyphenols, cold crashing or filtering the beer before dry hopping will help remove yeast, which will bind with certain hop polyphenols and not only reduce the flavor and aroma of the dry hops but the polyphenols that bind with the yeast are some of the same ones that will keep your beer from staling. It's lose/lose not to cold crash and/or fine before dry hopping.
- Since most of us are not filtering or adding advanced brewing chemicals like PVPP, alternative methods can be used to reduce polyphenols in the package, if that is your goal. Lagering will help drop out many polyphenols. Cold crashing will help but lacks the same effect of a longer cold period. Fining with gelatin, isinglass and Irish moss can also help drop out polyphenols. Silicon will also help clear out polyphenols but normally requires filtering afterwards.