How To - Determine Home Grown Hop Alpha Acid Levels

[katzke]

If you could predict bitterness of hops with a pH meter, dont you think that is the way it would be done?

Every micro and grower in the world would be doing it.

I bet the grower gets them tested in a lab by a different method because a pH meter does not work.

The tea method posted in the beginning is as close as one can get at home. I recall a different way of doing it but just could be remembering wrong.

Best way to use homegrown hops is to use them for flavor based on what your nose tells you. The amount of IBUs contributed by late additions is not great and if you are off a few % in hop AA then the difference is split by the low utilization. If you are using them for bittering and you are off by 50% you have a different beer.

Some homegrown hops are not even worth using. Let your nose be the judge.

Same advice for old hops. That old bag of hops in your freezer that says 10% AA sure isnt 10% today.

 

[Smashin]

Istarted a thread some time ago about my attempt to set up a conductometric titration of using methanolic lead acetate. I still have 19L of methanol and half a kil oof lead acetates sitting othe shelf.

THe method isn't all that antiquated nor is it nessesserily that inacurate as the method was used at bushy park until not that long ago.
In short i do intend to get back and finish what i started. Basically where i hit a stumbing block was obtaining an acurate enough conductivity probe for a reasonable price. I have one which measures in 10uS increments and essentially worked but just not accurate enough to define the intersection of the two lines. I believe a 1uS incremented conductivity meter would be suficiently accurate enough.

THis will surly bring the accedemically focused pointing out all sorts of inadequacies of the method and representivie sampling , etc ... blah blah blah, but for home brewing purposes i believe it is a usful mehtod. As it was for the commercial brewing industry for how many decades???

Anyway off to earn a quid.

Smashin

Won't work sorry, we are talking about very week organic acids that are basically insoluble in water.

Alpha Acids are not like strong acids (hydrochloric, nitric and phosphoric) they are called an acid because they have spare proton, Amino Acids ( the building block of protein), likewise. Neither is going to etch the concrete and you can't titrate for them.

It's dangerous to make assumptions based on just a name, take Sugar as an example, there are something like 2.6 million known "Sugars" all made up from the same basic 4 simple sugars, a small fraction of which would even be fermentable, many bare no resemblance to Sucrose, certainly aren't sweet and to most of us wouldn't be recognisable as sugars.

Here's one of the basic methods for measuring AA% in hops, there was an older method that used a Lead Acetate titration of an acidified methanol extraction of hops, it wasn't too accurate and has been replaced by the following or preferably a HPLC method like this one from the EBC

I really wish there was an easier way

MHB



Alpha and Beta Acids in Hops

(reference: ASBC MoA. 8th edition, 1992)

Method

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 dilB)/ (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) = 4.3

 

[Nick JD]

If you could predict bitterness of hops with a pH meter, don't you think that is the way it would be done?

Every micro and grower in the world would be doing it.

If you could make great beer for 50c a liter at home with simple equipment, surely no one would buy beer from the shop. Surely.