Hop Alpha Acid Testing (at Home)

[Smashin]

Has anyone successfully titrated their home grown hops to determine the Alpha acid content. I've geared up to test this years crop and am eagerly looking forward to seeing how the process goes. I'll be doing some trial runs this weekend on known a-acid (purchased) hops. Interested to hear of others success and/or failers....either way. :unsure:

 

[Guest Lurker]

Nope, but if you crack the method, be prepared for a bunch of people to send you samples of hops and some beer in return for a rating!

 

[Smashin]

Nope, but if you crack the method, be prepared for a bunch of people to send you samples of hops and some beer in return for a rating!

I have the method and apparently quite accurate, ingredients now in hand (very nasty, and under raps so far). Am yet to do a trail run or two. By all means if all goes well it would be a please to offer the service, free until proven!!!. I'll keep this post informed.

 

[jonocarroll]

I'd be particularly interested to see if the purchased one come in on target for a-acids. Not saying they won't, just wondering what the errors on these are, since people use these numbers to make their recipes. I'm also keen to know just how the home-grown varieties match up - I'd imagine it's quite difficult to optimise on such a small scale.

Care to divulge your plan to measure the a-acids? i.e. are these the only acids one would measure if one was to titrate with phenolphthalein?

 

[Smashin]

I'd be particularly interested to see if the purchased one come in on target for a-acids. Not saying they won't, just wondering what the errors on these are, since people use these numbers to make their recipes. I'm also keen to know just how the home-grown varieties match up - I'd imagine it's quite difficult to optimise on such a small scale.

Care to divulge your plan to measure the a-acids? i.e. are these the only acids one would measure if one was to titrate with phenolphthalein?

Quantum, i'm with your hence my search to find a method. This is my first year growing my own hops (goldings just hit top of wire today @ 4m, very exciting) hence i wanted to be able to use the cones acuratly and not just for flavour or aroma. I really hope this works, i have hunted long and hard (like most of us) and found diddly squat on the topic beyond HPLC etc...,

 

[ausdb]

I have the method and apparently quite accurate, ingredients now in hand (very nasty, and under raps so far). Am yet to do a trail run or two. By all means if all goes well it would be a please to offer the service, free until proven!!!. I'll keep this post informed.

Something along the lines of these, the second one does not look all that nasty?
Lead acetate / acetic acid

There is a slightly less laboratory like method described here which could be fun to do with a bunch of fellow brewers, maybe the westcoast berwers need to do the experiment the next time our members harvest their homegrown hops
http://home.netcom.com/~dluzanp/backyard.htm

 

[jonocarroll]

i have hunted long and hard (like most of us) and found diddly squat on the topic beyond HPLC etc...,

A cursory glance at the almighty google and it would seem that this is one of those few topics that doesn't have a million pages devoted to it (which in a way, is nice that it doesn't result in "ZOMG!1 HOP ALFA ACIDS SCUK!!"). From what I can see, titrating may not give you all the info - as I said, it will give you the total acidity - and Mass Spec/HPLC seems the way to go. UTas seems to have an organic chem group, perhaps you can get in touch with a bored postgrad and trade a brew or two for some help? ... Unless of course - you're the bored postgrad... <_<

I'd be keen to know your method, so if you aren't keen to post it, shoot me a PM.

Cheers! :icon_cheers:

 

[Smashin]

Something along the lines of these, the second one does not look all that nasty?
Lead acetate / acetic acid

There is a slightly less laboratory like method described here which could be fun to do with a bunch of fellow brewers, maybe the westcoast berwers need to do the experiment the next time our members harvest their homegrown hops
http://home.netcom.com/~dluzanp/backyard.htm

Ausdb, have you have experience in a-acid testing. Intersting in talking further.

 

[Smashin]

Ausdb, have you have experience in a-acid testing. Intersting in talking further.

Kit master - mmmmm bit low don't you think!!!!

 

[MHB]

I think the problem with the old titratiometric methods is that they measure more than just the A-Acid; a bunch of other stuff can also show up, depending on the age of the sample.
The fact that some of the reagents are fairly unpleasant doesnt help either, Lead Acetate is possibly the fastest way known to get lead into your system (well other than Tetraethyl Lead, and they wont even let us put that in cars any more)

UV/Vis spectroscopy is still pretty common and many large breweries still use this method, (Blue Tongue locally and Coopers that I have talked to) but HPLC is taking over. The price of good HPLC machines is coming down; the old nick name High Priced Liquid Chromatography is a bit less relevant.

HPLC (High Pressure Liquid Chromatography) with an internal standard appears to be the best method, at around $200 / sample; you have to really want to know.

Talking to one of the hop merchant a while ago and they get all their hops tested this way, so I think you can be fairly confident that the Harvest Alpha is going to be accurate, from then on its down to how well the hops are stored.
There was one other method involving optical rotation, but for some reason it appears not to have received much support, although it sounds interesting and could be explored further.

If anyone comes up with a home test kit that is reasonably accurate (as much as I would like to know) I would be getting a patent before I posted on AHB we are talking fairly serious money.
Good luck with that project it would be a great development.

MHB

 

[katzke]

I read a method for approximating your alpha acid, I've not yet tried
it, but it appears to make sense. Its semi- quantitative.

1) Make two teas from two different hops- one commercial hop
with a known A-acid, and one home grown. Both teas have exactly the
same quantiy of hop and water (say, a few grams of hop per half pint
boiling water). Both are left to stand for equal times before
removing the hops.
2) Allow the teas to coo to room temperature
3) Make up a large stock solution of sugar syrup
4) Start by drinking the home grown hop tea- add sugar syrup
until the sweetness is the prevailing taste, overriding the
bitterness. Accurately record the quantity of sugar syrup added.
5) Allow your taste buds time to recover, then repeat with
commercial (known A-acid) hop tea.


6) Calculate your alpha acid content thus :

(acid_B / sugar_B) x sugar_A = acid_A

Where
Acid_B is the known Alpha acid content of the commercial hop
Sugar_B is the volume of sugar syrup added to the commercial hop tea.
Sugar_A is the volume of sugar syrup added to the commercial hop tea.
Acid_A is the known Alpha acid content of the home-grown hop

 

[drsmurto]

Titration is a tad outdated. As others have said, you will get total acid content unless you have a way of selectively chelating the alpha acids.

I doubt Pb2+ would do the trick.

HPLC - high PERFORMANCE liquid chromatography (not sure where high pressure came from) works well, if it was me running the experiment i would use GC-MS.

But have fun Smashin, your 1st year crop is likely to yield a few grams only so the AA content is not all that important.

 

[MHB]

Its been a dozen some years since I played with one of these, but you had me thinking my brains had turned to mush and its the time of year for that.

HPLC Definition from Wiktionary
(analytical chemistry) high performance liquid chromatography or high pressure liquid chromatography

[edit] Quotations For examples of the usage of this word see the citations page.

[edit] See also chromatography
Retrieved from "http://en.wiktionary.org/wiki/HPLC"

And yes its mostly called high performance liquid chromatography these days, showing my age

Cheers

MHB

 

[Online Brewing Supplies]

Swan Brewery in Perth use to do it for about $70, but that was in a beer tested for IBU's.So to test your hops before brewing.I just dont know.
GB

 

[ausdb]

Hi Guys

Sorry no epxperience of home alpha acid testing I just was googling and found that stuff, but the hop tea experiment seems like a good idea amongst the members of our brewclub as a lot of them grow their own hops. Personally I have given up on hop farming after three failed seasons

 

[Smashin]

Titration is a tad outdated. As others have said, you will get total acid content unless you have a way of selectively chelating the alpha acids.

I've done some further digging around and found a few publications on the topic, interestingly it saems that Methanolic Lead acetate selectively precipitates out of solution with humulones (alpha acids) with the lupulones (beta acids) remaining in solution so the results are representative of bittering power (to a point). Fresh young hops bittering power is well characterised by the a-acid content. As hops age and the a-acid content deteriorates high beta % hops will give beer with higher percieved bitterness than low beta % hops. Beta acids oxidise over time producing compounds that do contribute to bittering. These compounds precipitate with lead acetate contributing to the a-acid calculation, in this way the LCV is quite a good test for hop bittering power young or old.


I'm nervously setting up the lab to ensure no lead acetate get lost or on me. Think i'll lock the door with 000 on speed dial just incase i cant get the last 2 no.s dialled..lol :icon_vomit:

 

[Ginger NZ]

I read a method for approximating your alpha acid, I've not yet tried
it, but it appears to make sense. Its semi- quantitative.

(detail removed)

(acid_B / sugar_B) x sugar_A = acid_A

Where
Acid_B is the known Alpha acid content of the commercial hop
Sugar_B is the volume of sugar syrup added to the commercial hop tea.
Sugar_A is the volume of sugar syrup added to the commercial hop tea.
Acid_A is the known Alpha acid content of the home-grown hop

IIRC, this is similar to the method for measuring scoville units in chillis.

 

[drsmurto]

Its been a dozen some years since I played with one of these, but you had me thinking my brains had turned to mush and its the time of year for that.

HPLC Definition from Wiktionary
(analytical chemistry) high performance liquid chromatography or high pressure liquid chromatography

[edit] Quotations For examples of the usage of this word see the citations page.

[edit] See also chromatography
Retrieved from "http://en.wiktionary.org/wiki/HPLC"

And yes its mostly called high performance liquid chromatography these days, showing my age

Cheers

MHB

You learn something new every day.

I've used HPLC (and GCMS) quite a bit but have never come across the pressure description.


Smashin - as far as lead acetate chelating a-acids vs b-acids thats all well in good (if you have a reference for this i would appreciate a look at it) but you are still assuming they are the only 2 acid compounds present in a hop.......

 

[MHB]

From Brewing Science and Practice

8.2.3 Analysis of the hop resins
Procedures for the estimation of the total resins, total soft resins, and hard resins, by difference, (see definitions above) in hops and hop products are given in Analytica-EBC but since it was found that the A-acids are the most important brewing principles few brewers bother to measure the total and soft resin contents. The _-acids were originally estimated gravimetrically as their lead salts but since the precipitate is soluble in excess of the lead acetate reagent, trials had to be made so that only the correct amount of reagent was used making it a lengthy process.

View attachment 23432

It was found that if the conductivity of a methanolic solution of the A-acids was measured during titration with methanolic lead acetate solution it did not increase until there was an excess of the reagent. Thus if regular aliquots (0.20 ml) of the methanolic lead acetate reagent (2 or 4%) are added and the conductivity measured after each addition, a graph can be drawn where the intersection of the two straight portions provides the endpoint (Fig. 8.5). The absolute value of the conductivity is not needed and the lead acetate reagent can be standardized by a similar titration against 0.100 N sulphuric acid. The shape of the graph is different in the presence of other solvents, so, in the approved method, pyridine (1 ml) is added to the titration. The conductivity may be plotted against the volume of the reagent on Cartesian coordinate paper (Fig. 8.5) or the resistance may be plotted directly on to reciprocal ruled paper. Since the reaction of lead acetate is not specific for A-acids, the result is expressed as the Lead Conductance Value (LCV). However, with fresh hops the LCV is very similar to the A-acid content but, as hops age on storage, oxidation products are formed which may react with lead acetate.

Hope that helps

MHB

 

[unterberg]

I have done some HPLC and depending on what application you use you will have different columns and hence different working pressure.
With the reverse phase column I used to have quite high pressures but using an size exclusion column you cant do high pressures.