BREWING
O O
O O
O O
H
OH
R
R
R
Oxidation
HO
HO
Wort Boil
HO
OH
O
O
OH
OH
OH
iso- α -acid
α -acid
Humulinone
The Structure of Humulinones, Iso- α -acids and α -acids (Adapted from Wolfe 2012)
Taste and nish Dry hopping increases the concentra- tion of polyphenols in beer. At higher addition rates the concentration of hop-derived polyphenols comes quite close to matching that contributed by the malt. The effect of polyphenols on the taste of beer has been mired in controversy. Recent studies by Oregon State University, USA and Research Institute of Malting and Brewing, Czechia have found hop polyphenols are not only bitter and astringent themselves but also cause the bitterness imparted by iso- α -acids to be perceived as harsher and more lingering. On the other hand, work at Leuven University, Belgium found that except for the proanthocyanidins, polyphenols derived from spent hops were highly avour-active, with positive effects on mouthfeel. Most people in white coats tend to agree that polyphenols and especially proanthocyanidins are likely candidates for imparting bitterness and astringency. Levels of polyphenols vary across hop varieties and areas of cultivation – and as yet are not part of the analysis sheet you receive with your hop contract. Most sensory work on dry hopped beer has found that it rates more bitter than the beer before dry hopping. Interestingly, most studies have found that the concentration of iso- α -acids actually falls after dry hopping, with (up to a point) the reduction proportionate to the rate of dry hop applied. It is likely therefore that the drop is due to the iso- α -acids adhering to the plant material of the dry hops and being removed with it. Strange that sensory bitterness should increase then I hear you say. So why does it? Because α -acids are sparingly soluble – and an increase up to 22ppm has been shown to have no impact on sensory bitterness – we can rule them out – unless you are practicing extreme dry hopping (yes, there is such a thing). Oxidised β -acids (hulupones) were at one point thought to also be signi cant,
but current thinking is that although they are pretty bitter, they are insuf ciently soluble in beer to have a real impact. Another culprit has been identi ed – humulinones – which are found in hops and are the result of peroxidation of α -acids. On a molecular level they look fairly similar to iso- α -acids. Humulinones are found in pel- letised hops in greater concentrations than in whole cone hops as a result of the rigors of pelletisation. They are more soluble (around 87% extracted after three days static dry hopping) in beer than iso- α -acids and have been reported as being 0.66 times as bitter. Humulinones-derived bitterness has been found to be smoother and less lingering than that of iso- α -acids. This was put down to humulinones being more polar and hence less likely to stick to oral membranes. A new formula has been developed to calculate the bitterness of beers which have been dry hopped which includes alpha acids and humulinones.
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Lupulin glands
way you believe(d) cohumulone gives an unpleasant bitterness. Another fun fact to note about humulinones is that they absorb UV at around the same wavelength as iso- α -acids, so will increase your IBU measurement if you are using the spec- trophotometric method. As with everything in brewing a lot depends on what you are doing. If you are using 200g/hL of Hallertauer Mittelfruh, the bitterness perception of the beer is not really going to change to the point where it’s too bitter to sell. If you are using Pahto at 2kg/hL it may well be too bitter for the average palate. A recent study quanti ed the effects of extreme dry hopping, which is unscienti cally de ned as dry hop addition rates of above 1.5kg/hL. The study found that in a beer originally containing 42mg/l iso- α - acids, dry hopped with 2.3kg/hL of
Bitterness = ppm IAA + (ppm AA x 0.1) + (ppm H x 0.66)
IAA = iso- α -acids AA = α -acids H = humulinones
Although it sounds eminently plausible, there have only been a few studies carried out on humulinones and beer bitterness so you might want to believe they have the stated impact in the same
Spicy/Herbal
Floral/Fruity
Citrus/Pine
Humulene Humulene Epoxide I Humulene Epoxide II Humulene Epoxide III Humulenol II Humulol Caryophyllene Oxide Myrcene Eudesmol Farnesol Ethyl cinnamate
Linalool Geraniol Geranyl Acetate Geranyl Isobutyrate Citranellol β -Ionone Nerol γ -nonalactone 4mmP Ethyl 4-methylpentanoate β -damascenone
Limonene Citral Farnesene
α -Pinene Citranellal Linalool Ethyl 4-methylpentanoate Ethyl butyrate
Table 1: Components of Hop Essential Oils (Adapted from Wolfe 2012)
october 2019 I BREWER AND DISTILLER INTERNATIONAL ● 39
i bd.org.uk
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