How To Test AA ?

[Pjam]

I've been given some hops but I don't know their AA. How can I test? Is it really this difficult? :hmm:

1. Place 5.000 +/- .001 gr pulverized hops in an extraction bottle and add 100 mL toluene.
2. Shake for 30 min with vigorous agitation.
3. Let stand until clear or centrifuge (preferred).
4. Dilution A: Dilute 5.0 ml of this extract to 100 mL with methanol.
5. 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.
6. Immediately read dilution B (1 cm) at 275, 325 and 355 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:
1. 5 gr hops extracted with 10 mL toluene
2. 5 mL clear extract diluted to 100 mL with methanol=Dilution A
3. 3 mL Dilution A diluted to 50 mL with alkaline methanol
4. Absorbances
o A355=0.615
o A325= 0.596
o 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) = 4.3josephus

 

[rpt]

I think the old method was to compare it to a hop of known bitterness. Boil up a sample of each. Keep diluting the more bitter one until it tastes the same as the other sample. From the amount of dilution you can calculate the AA%.

 

[Aleman]

I've been given some hops but I don't know their AA. How can I test? Is it really this difficult?

Yes it really is that difficult . . . and note that it requires a UV Capable spectrophotometer, a standard one will not cut the mustard.

Brewers of old didn't know the alpha acids either, just use the 10 year average for the variety you have that will be close enough

 

[Pjam]

OK thanks.

So without the right tech I guess my best method might be to 'stuck it and see'. Perhaps try a single hop brew (start, middle and end) and compare it to another known single hop brew.