Hops

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(In progress)

Hops are a dioecious climbing bine, meaning that they have separate male and female plants. The female cones are used in beer for flavor as well as for antimicrobial properties. Need info on hops and how they pertain to alternate brewing methods, yeasts, and bacterium

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://www.ncbi.nlm.nih.gov/pubmed/25475328
  3. http://onlinelibrary.wiley.com/doi/10.1002/jib.40/full
  4. Kowaka, K., et al. "true value of aroma hops in brewing." Proceedings of the congress-European Brewery Convention. 1983.
  5. http://www.asbcnet.org/publications/journal/vol/abstracts/43-25.htm
  6. https://www.facebook.com/groups/MilkTheFunk/permalink/1228610483833830/
  7. https://www.facebook.com/groups/MilkTheFunk/permalink/1234538973240981/

Hop Composition

-Makeup of hops: quick overview of alpha acids, iso-α-acids, beta acids, oils, other compounds

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.

Sakamoto and Konings (2003) attributed the antimicrobial effects the iso-α-acids acting as ionophores to cause leaking of ions across cell membranes. 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. The protonated iso-α-acids are antimicrobially active by crossing into the cell and dissociating (releasing the H+ ion from the iso-α-acid), therefore disrupting the cellular proton gradient which is necessary for cells to function, before 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. This resistance to hop antimicrobial activities through iso-α-acids appears to be stable within bacteria with the trait, and 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[1].

(in progress) Another antimicrobial mechanism resulting from oxidative stress has been attributed to both iso-α-acids and humulinic acids[2]. 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 between Mn2+ ions and specific hop acids within the cell, which is due to different conditions inside (higher pH, higher Mn2+) and outside (lower pH, lower Mn2+) of the bacterial cell[3][2]. Iso-α-acids or humulinic acids passing into the cell, form complexes with Mn2+ and transfer electrons out of the cell[3]. 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[2].

Bacterial Resistance to Hop Compounds

(in progress) 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[3]. Anitmicrobial resistance of bacteria will vary by species as well as within a species with individual strains. Because of this intra-species variability and as yeast labs do not identify cultures by uniform strain IDs, it is therefore difficult to give specific advice about the hop-tolerance of a wide range of strains offered from different sources. The environment in which strains are cultured and maintained may also influence their hop tolerance (---source---). Typically Lactobacillus brevis is more hop tolerant than other Lactobacillus species such as L. delbrueckii (----source---).

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, including bitterness from oxidized alpha and beta acids.

Chemistry

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 [4] (~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[5] (~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[6]. 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 [7] (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)[6]

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[6]. Considering the difference in strength in German and Belgian hops[7], 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[6]. 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[6].

(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

See Also

References

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