Hops

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(In progress)

Hops are a dioecious (meaning that they have separate male and female plants) climbing bine whose female cones are used in brewing for flavor as well as for antimicrobial properties. Sour and funky brewers can use hops to help regulate lactic acid bacteria and control acid production to desired levels, especially in aged mixed-fermentation or spontaneous fermentation beers. Brewers who are interested in rapid acid production using quick/kettle souring techniques such as sour worting may wish to limit or avoid hop use before acidifying so that sufficient acid is produced on timescales of hours to a couple days.

Potential references (https://www.facebook.com/groups/MilkTheFunk/permalink/1190513557643523/?qa_ref=qd&comment_id=1195663997128479&comment_tracking=%7B%22tn%22%3A%22R%22%7D):

  1. http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1970.tb03259.x/abstract
  2. http://onlinelibrary.wiley.com/doi/10.1002/jib.40/full
  3. Kowaka, K., et al. "true value of aroma hops in brewing." Proceedings of the congress-European Brewery Convention. 1983.
  4. http://www.asbcnet.org/publications/journal/vol/abstracts/43-25.htm
  5. https://www.facebook.com/groups/MilkTheFunk/permalink/1228610483833830/
  6. https://www.facebook.com/groups/MilkTheFunk/permalink/1234538973240981/

Hop Composition

(in progress)

The main compounds of interest to brewers in hops are their bitter acids and oils. Alpha acids account for roughly 2-12% of dried hops by mass, beta acids account for roughly --- % and oils account for roughly 0.5-3%, though the exact percentages will vary depending on factors such as the hop varietal, growing region, harvest time, and growth conditions for the year.

The primary alpha acids (humulones) in hops are humulone, cohumulone, and adhumulone. The ratio of these individual acids to each other can vary much like total iso-α-acid percent, though generally the primary acids are -------. While alpha acids are insoluble in wort, the isomerized acids which are formed during boiling are soluble. Isomerization leads to roughly a 70%/30% split between cis and trans iso-α-acids respectively, with cis iso-α-acids being more stable over time and more bitter[1]. Alpha acids themselves do not taste bitter, but isomerized alpha acids (iso-α-acids) contribute to the bitterness of beer and have antimicrobial properties. Isocohumulone is often cited as being more harshly bitter than the other iso-α-acids, but studies of taste perception of individual iso-α-acids have not agreed with this. However Isocohumolone is slightly more soluble than the other acids and therefore a hop with a higher cohumulone composition may result in a beer with higher iso-α-acid for hops of equal iso-α-acid percent and use in brewing but different iso-α-acid breakdown[1]. Alpha acids are susceptible to oxidation and the alpha acid content of a hop will decrease with storage.

Beta Acids (lupulones) are similar in structure to alpha acids and have the analogous individual beta acids (lupulone, colupulone, adlupulone) to individual alpha acids. Beta acids are not able to isomerize and are therefore not soluble in wort unless they are chemically modified by a process such as oxidation. Oxidatized beta acids are soluble and can contribute to bitterness in beer. Oxidized beta acids are discussed more under aged hops.

There are three primary classes of oils in hops: hydrocarbons (~64% of the total oils), oxygenated compounds (~35% of the total oils), and sulfur compounds (≤1% of the total oils)[2]. Individual flavor and aroma active oils each have different thresholds, solubilities, and volatilities, and individual oils can have synergistic interactions with each other. The chemistry of hop oil taste perception is therefore very complicated and overall is not well understood. While sulfur compounds make up only a very small fraction of the total oils, they have a significant impact on hop flavor[2].

Antimicrobial Properties

Hops are known to have antimicrobial properties against gram positive bacteria. This includes bacteria which can be present in beer both as spoilage organisms and as intentionally added in sour and mixed fermentation beer such as Lactobacillus and Pediococcus. Certain other bacteria found in beer such as Acetobacteraciae are gram negative and are not susceptible to the antimicrobial properties of hops. Certain Gram posotive bacteria are known to be more resistant to the antimicrobial effects of hops. Multiple mechanisms have been proposed to explain why hops are antimicrobially active.

One mechanism of the antimicrobial activity of hops is due to the role of alpha acids and similar hop acids (such beta acids and iso-α-acids) as ionophores, or compounds which can transport ions across cell membranes[3] [4]. The protonated iso-α-acid (the form of the acid with an associated H+ ion, an H+ ion is a proton) is the antimicrobially active form. This means that for a beer with a given iso-α-acid concentration, the antimicrobial effects will be stronger at lower pH values because a greater percentage of the acid will be protonated. Protonated iso-α-acids act against bacteria by crossing into the cell and dissociating (releasing H+ ions from the iso-α-acid), therefore disrupting the cellular proton gradient which is necessary for cells to function, before binding an equal charge in metal ions and crossing back out of the cell. Cells with a resistance to hop bitter acids are better able to eject undissociated iso-α-acids from the cell and therefore preserve their proton gradients. The mechanism to expel iso-α-acids appears to be specific toward this type of compound rather than by a more general antimicrobial resistance mechanism such as multi-drug resistant bacteria possess[4]. Hop resistant bacteria cultured in the absence of hop acids can lose their resistance if grown in an environment without antibacterial hop compounds[3] and some hop resistant microbes need to be acclimated to hop acids by growth in sub-limiting levels of antibacterial acids before they are able to resist higher levels[4].

(in progress) Another antimicrobial mechanism resulting from oxidative stress has been attributed to both iso-α-acids and humulinic acids[5]. Humulinic acids are either not bitter tasting or much less bitter than iso-α-acids but are similar in structure to and are formed from the degradation of iso-α-acids. This oxidative stress-driven antimicrobial activity is due to potential for oxidation-reduction (redox) reactions within bacterial cells between Mn2+ ions and these specific hop acids. The redox potential is due to different conditions inside (higher pH, higher Mn2+) and outside (lower pH, lower Mn2+) of the bacterial cell[6][5]. Iso-α-acids or humulinic acids passing into the cell, form complexes with Mn2+ and transfer electrons out of the cell[6]. By targeted molecular modifications Schurr et al. (2015) determined that the Mn oxidative stress-driven antimicrobial effect of iso-α-acids was more important than antimicrobial effect of the ionophore proton transfer discussed above in the overall antimicrobial activity of hops[5].

Bacterial Resistance to Hop Compounds

Due to the multiple mechanisms for hop antimicrobial activity, multiple resistance mechanisms are necessary for a Gram-positive bacterial cell to successfully be hop-tolerant[6]. Hop resistance of bacteria will vary by species as well as within a species with individual strains. The environment in which strains are cultured and maintained may also influence their hop tolerance. The hop tolerance of lactic acid bacteria strains decreases when they are cultured in hop-free environments and strains cultured in media with increasing concentrations of hop compounds show an increase in hop tolerance[4]. the stability of hop resistance, or the rate at which it is lost when bacteria are cultured in unhopped wort, varies by strain. It can take up to 1 year for maximum loss of hop resistance, suggesting that in some strains have a relatively stable hop resistance[4]. Because of this intra-species variability and dependence on how the strains were cultured, it is difficult to give specific advice about the hop-tolerance of a wide range of strains offered from different sources. As a general rule, some common lactic acid bacteria species used in sour beer and found as beer spoilage organisms like Lactobacillus brevis, Lactobacillus lindneri and Pediococcus delbrueckii have some resistance to hops[4]. Brewers seeking to make acidic beers with higher doses of hops may wish to seek out one of these species. Some hop-tolerant species benefit from pre-culturing in media with below-limiting concentrations of compounds before being used in more highly hopped wort or beer[7].

Aged Hops

Aging hops leads to oxidation of acids and oils. Generally brewers seek to avoid this to preserve the aromatic and bittering properties of their hops; however some beer styles make extensive use of aged hops. Aged hops still retain some antimicrobial properties and can be used for microbial inhibition. In addition to their antimicrobial activity aged hops contribute important flavor and aroma compounds and precursors to beer.


Chemistry

(in progress)

Acids: oxidized alpha acids (humulinones) are similar in taste perception to iso-α-acids[2]. Oxidized beta acids (hulupones) also contribute to perception of bitterness.

Oils: cheesy oxidation compounds which can be esterfied to form fruity tasting compounds[2].

Aged Hops in Lambic

Modern lambic traditionally uses aged hops at a moderate rate to help limit and select for microbes and regulate acid production. Modern Lambic brewers cite rates in the range of roughly 450 grams of hops per Hl of finished beer [8] (~43 min in) (see also the notes pertaining hopping rates on the Cantillon page), with some brewers possibly going above this range. The age of hops used depends on the producer and their preferences/stock. Cantillon uses hops that are on average 2-3 years old (source----), which 3 Fonteinen reports using hops that are over 10 years old[9] (~48 minutes in).


http://researchmap.jp/?action=cv_download_main&upload_id=55765

Historic hopping in lambic and other mixed-fermentation beer

While modern lambic uses aged hops almost exclusively, it was common for historic lambic to blend both aged and fresh hops[10]. The exact ratio of fresh to aged hops changed over time and could vary depending on the harvest (poor hop years may have relied more heavily on aged hops while years of good harvests would make more use hops of the recent harvest). In addition to the difference in hop age between modern and historic lambic, hopping rates also differ significantly between modern and aged hops. It is important to note that the quality of these hops are certainly different from modern hops, and that hop origin could have a significant influence on suggested hopping rates [11] (see the hopping rate table and notes regarding hop origin conversion factors from historical texts). While hop quality would have improved moving to the modern day while hopping rates were dropping, there is mention in historic lambic literature of lambic in the late 1800s being more bitter than lambic from the mid 1900s (and, subsequently, similar to historic saison in the increased hop presence in a mixed-fermentation beer)[10]

Historical documents dealing with Belgian brewing show a steady progression from high doses of fresh hops in lambic to the sort of hop composition and origin that are in use today. In 1851 Lacambre mentions rates for Belgian hops of 760-860 g/Hl and specifically highlights the use of young hops. Belgian brewing scientist Henri Van Laer recommended a hopping rate of 700-800 g/Hl in 1890, roughly in agreement with Lacambre though slightly lower. In the early 1900s, citing information from 1896, Le Petit Journal du Brasseur mentions a hopping rate of 540 g/Hl using a mix of Belgian and Bavarian hops and a split of 2/3 young, 1/3 old in good years (and 50/50 in bad years). In 1928 Le Petit Journal du Brasseur recommends a larger proportion of aged hops (2/3 aged, 1/3 fresh) and rates of 600g/Hl of Belgian hops[10]. Considering the difference in strength in German and Belgian hops[11], this fits with a stable or decreasing hopping rate from that given in the early 1900s. In 1937 exclusive use of aged hops is recommended, though as noted in 1946, year old hops may be preferable to hops that were aged longer in poor conditions[10]. Also in the 1940s Le Petit Journal du Brasseur recommends hopping rates of 400-500 g/Hl, roughly in agrement with modern times, and notes that the lambic of this time was softer than historic lambic[10].

(In Progress) Lambics aren't the only historic mixed-fermentation beer to make use of aged hops. Though the specific mention of aged hops for saison and bieres beers does not seem to be the norm, aged hops were used at times, such as when more acidity was desired. These hops were also more likely to be used toward the beginning of the brewing season in months like October where the current harvest may have been considered too fresh for proper use. Notes: Give some discussion of hopping saison and bieres de garde. See hopping grisette table for some hopping rates, PJB, etc.

Aged Hop Suppliers

Glycosides and Brettanomyces

Hops contain glycosides, which are flavor compounds that are bound to a sugar molecule. In their bound form, glycosides are flavorless. Enzymatic activity from some strains of Brettanomyces can release these bound compounds and release their flavor and aromatic potential. See the Brettanomyces page for details.

Techniques

Dry Hopping

(in progress)

Dry hopping can contribute to bitterness in beer through oxidized alpha acids and oxidized beta acids[2].

See Also

References

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