Hop chemistry, hop selection and the role of hops

Hop varieties

• Aroma hops: a lower alpha acid, oil profile associated with good aroma. a finishing or conditioning hop
• Bittering hops: a higher alpha acid. used in the boiling process
• Continental or Noble hops: mostly used for lagers. soft bitterness, spicy, floral, subtle herbal. ex) Hallertau, Tettnang, Spalt, Czech Saaz
• English hops: lower alpha acid, floral, more grassy, fruity ex) East Kent Goldings, Fuggle, Challenger, Target, Progress
• American hops: bright, fruity, resinous, dual purpose hops(high alpha acid+pleasant aroma) ex) Cascade, Centennial, Chinook, Willamette, Amarillo 

The role of hops in brewing

• being isomerized(need boiling process): add bitterness
• supplying tannins: take away unwanted proteins, more clear and stable
• antimicrobial 
• allowing strong boil without foam 
• add flavor and aroma
• enhance mouthfeel
• increase head retention via isohumulones
• natural filter
• prevent boilover: put 10% of bittering hops at the beginning of boiling process

Anatomy of a hop cone

• Bracts and bracteoles = leaf
• lupulin glands: yellow sticky powder. contain the resins and oils
• 3 main chemical groups: Alpha acid(humulones)+Beta acid(lupulones)+Essential oils

Alpha acids

• Humulone+Cohumulone+Adhumulone
• 2 primary functions: adding bitterness+prevent unwanted growth of bacteria
• 15~18% generally high percentage of alpha acids
• 4% for noble hops
• Isomerization: convert the alpha acids into iso-alpha acids
• Iso-alpha acid+ultraviolet light->skunked flavor(especially in clear or green bottles) 

Beta acids

• Lupulone+Colupulone+Adlupulone
• oxidation rather than isomerization: long fermentation, storing, dry hopping, barrel aging
• antiseptic qualities
• noble hops have 1:1 alpha:beta ratio
• that's why it's suitable for European lager(with long storing)

Essential oils

• 3 major classes of essential oils in hops: 
• Hydrocarbons
• Oxygenated Hydrocarbons
• Sulfur-containing hydrocarbons

Hydrocarbons

• up to 80% of hop oil in fresh hops
• Myrcene: the largest component, citrus and pine character. low in noble type, high in American varieties(Colombus, Amarillo)
• Humulene: delicate and refined, elegant. high in noble hops(European). herbal and spicy character
• Caryophyllene and Farnesne: clove and rosemary(caryophyllene), woody and earthy(farnesne, like fuggle hop)

Oxygenated Hydrocarbons and Sulfur-containing hydrocarbons

• Oxygenated Hydrocarbons: from late hop additions, like linalool(hoppy), geraniol(floral, rose)
• Sulfur-containing hydrocarbons: unpleasant flavor. most evaporate in the boil but attributed when late or after the boil ex) mosaic

Hop oils

• hop characteristics change with aging and oxidation
• store hops in a cold environment
• HSI: decrease of alpha acid per time

Hop products

• whole leaf hops: subtle, fresher. difficult to store and less stable. use within a day
• pelletized hops: Type90(T-90) means 90% of hop cone, mostly used. Type45 has dense alpha acids and oil. use within months
• hop extracts: achieved through the use of organic solvents or CO2. use within years

hop extracts

• pre-isomerized hop extracts:
• Normal form: alpha acid have been separated from resin, isomerized
• Novel form: alpha acid are isomerized still in the resin. good utilization(70%) but expensive
• pros: reduced transport cost, high utilization, stability for finished beer, reduce wort loss, reduce tannin and phenol 
• cons: increase production cost, possible inclusion of solvents, bad customer reputation(bc unnatural), decrease in subtlety and freshness of hop

hop additions

• most of the hop oils are lost during the first 20 mins
• if hop oils in too concentration, steamed vegetable or grassy character present
• when certain aroma or flavors are wanted, add hops near the end of boil
• Isomerised alpha acids(mg/l)
• Iso-humulone(=IBU)
• production of over 90% of wort bitterness occurs within the first 30 mins and need 60~75 mins for complete extraction

hop utilization

• hop utilization(%)= iso a acids in beer*100/ a acids added to kettle
• generally 30%(boil time 60~74 mins+pellet)
• it depends on: 
• the kind of hop product: extract>pellet>wet hop
• the intensity and length of the boil: longer, hotter boil=higher utilization
• wort gravity: lower gravity, higher utilization
• wort pH: high pH(fast isomerization+side effect), low pH(slow iso)
• proteins present: high protein(wheat, oats)=low utilization
• amount of hop used: high hopping rate, low utilization
• and during fermentation, low utilization

Calculation IBU

• IBU=Woz.*U%*A%*7489 / Vgal.*Cgravity
• Woz. = Vgal*Cgravity*IBU / U%*A%*7489
• Woz. weight of hops(oz)
• A% alpha acid level
• U% percent utilization(generally 30%)
• Vgal. volume of final wort(gallon)
• Cgravity correction for gravity:
• Cgravity=1+[(actual gravity of wort-1.050)/0.2]

Formulation Hop Bill

• determine target IBU
• determine amounts of aroma and flavor hops
• determine IBU contributions of aroma&flavor hops and subtract it
• determine amounts of bittering hop

Using Aroma hops

• boiling: from 2 to 30 mins. fresh hop oils vaporized but spiciness and floral compounds formed through oxidation
• steeping: commonly whirlpool and hopback(hop rocket)
• dry hopping: add during fermentation or aging. 

mason jar as hop back