Alpha and Beta Acids in Hops
(reference: ASBC MoA. 8th edition, 1992)
Method:
- Place 5.000 +/- .001 gr pulverized hops in an extraction bottle and add 100 mL toluene.
- Shake for 30 min with vigorous agitation.
- Let stand until clear or centrifuge (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 325nm and 355nm falls within the most accurate range of the instrument.
- Immediately read dilution B (1 cm) at 275nm, 325nm and 355nm vs a toluene blank that was prepared and diluted in EXACTLY the same manner.
Notes:
- Hexane may be substituted for toluene
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)
Example:
- 5 gr hops extracted with 10 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
- Absorbances:
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%
