Hop bitterness analysis

ref : ASBC methods of Analysis, 8th Edition, 1992.

Hop bitterness in beer (ASBC Method)

• Transfer 10.0 mL beer to a 50 mL centrifuge tube.
• add 50 uL octyl alcohol, 20 mL isooctane (HPLC grade) and 1 mL 3M HCl .
• shake vigorously for 15 minutes.
• centrifuge to separate the phases.
• read organic phase at 275 nm (1 cm cell) vs blank (20 mL isooctane, 50 uL octyl alcohol).

BU= Abs @275*50

Example: Abs =0.622 -- 0.622*50= 31.1 BU

Notes:

1. isooctane should have an Abs@275 <0.005.
2. readings should be done ASAP due to decomposiotin by UV light

Alpha and Beta acids in hops: ASBC MoA Method

• place 5.000 +- .001 gr hops in an extraction bottle and add 100 mL toluene
• shake for 30 min with vigorous agitation
• let stand until clear or certrifuge (preferred)
• Dilution A: dilute 5.0 ml of this extract to 100 mL with methanol.
• Dilution B: dilute an aliquot of the dilution A with alkaline methanol (0.2 mL 6M NaOH per 100 mL MeOH) so that the Abs at 325 and 355 falls within the most accurate range of the instrument.
• Immediatly read diluion B (1 cm) at 275, 325 and 355 vs a toluene blank that was prepared and diluted in EXACTLY the same manner.

Calculations

dilution factor, d= (volume dil A x volume dil B)/ (500 x aliq extract A x aliq dil A)

% alpha acids= d x (-51.56 A355+ 73.79 A325-19.07 A275)

% beta acids= d x (55.57 A355-47.59 A325 + 5.10 A275)

• 5 gr hops extracted with 100 mL toluene
• 5 mL clear extract diluted to 100 mL with methanol=Dilution A
• 3 mL Dilution A diluted to 50 mL with alkaline methanol
• A355=0.615
• A325= 0.596
• A275=0.132
• d = (100 x 50) / (500 x 5 x 3) = 0.667
• alpha = 0.667 x [ -(51.56 x 0.615) + (73.79 x 0.596) - (19.07 x 0.132) = 6.5
• beta = 0.667 x [ (55.57 x 0.615) - (47.59 x 0.596) + (5.10 x 0.132) = 4.3

Alpha and Beta acids in hops by HPLC: ASBC MoA Method

detector:

capable of 314 nm

column:

C18 (they recommend 250x4mm, 5 um ODS, RP18, Nucleosil-5)

Mobile phase:

MeOH: H2O: HPO4 (85%) /85:17:0.25 (v/v)

Conditions:

isocratic

Flow:

0.8 mL/min

Temp:

ambiant

Sample:

10 uL

Method: