How To - Determine Home Grown Hop Alpha Acid Levels

[pdilley]

Needed:

o 28 grams home grown hops (28.3 grams if you have accurate scales)
o sugar
o water measure in mL


Accurately measure:
28.3 grams of your home grown hops.
473 mL of water


Steps to make hop tea:
Boil the water for 15 minutes with 1 accurately measured tablespoon of sugar added.
Add your home grown hops and boil for 10 additional minutes.
Strain out the hops leaving you with hop tea.


Method to estimate alpha acid bitterness levels:
Mix 59mL of your hop tea with with 59mL of water.
Sip.
Taste bitter?
Mark a 1 on a piece of paper.
Take 59mL of this diluted mixture into a new cup and add 59mL additional water.
Sip again.
Taste bitter?
Mark another 1 on the piece of paper.
Take 59mL of this new diluted mixture into a new cup and add another 59mL of additional water.
Sip.
Taste bitter?
Mark another 1 on the paper.

Continue until you no longer taste bitterness.

Add up all the ones to get a final number.

That is your ballpark figure to brew with as %AA in your recipes.


Cheers,
Brewer Pete

 

[jyo]

I was reading about a year ago of a more 'scientific' way to determine AA at home, and I thought I had saved it on the puter....I can't find it, but I'll be back.

 

[jyo]

Sorry, forget it. I can't find it, and the only other info I can dig up requires liquid chromotology :wacko:

I did come across your method on a few other sites just now too, Pete. It was suggested to try this method first using a commercially grown hop with a known AA. Then trying it with your homegrownies.
Cheers, John.

 

[MarkBastard]

Problem is it depends on how good you were at drying them surely?

Oh and 28.3 grams of home grown hops going to waste? Nawww!

 

[Nick JD]

Would it be possible to simply make a solution at a standard concentration and then take a pH reading?

Do AA% vary enough to change the pH of a solution?

Does 1g of 4% Saaz have a higher pH than 1g of 11% Chinook?

 

[simon.sillitoe]

Would it be possible to simply make a solution at a standard concentration and then take a pH reading?

Do AA% vary enough to change the pH of a solution?

Does 1g of 4% Saaz have a higher pH than 1g of 11% Chinook?

I was thinking a titration... but then again that's still a little difficult at "home", and I have nfi what appropriate indicators/titrate would be.

 

[MHB]

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]

It's dangerous to make assumptions based on just a name...

Maybe if you are a bomb disposal tech ... wondering whether to cut the blue or the red wire but this is just brewing beer isn't it?

If the tongue can guess the difference between say, 10IBU - surely that's a measurable acidity with simple equipment?

If 10g of X hop boiled for 60 minutes = 30IBU, and another Y = 15IBU ... what's the difference in AA%? I'm thinking X = 2Y.

I like Brewer Pete's method more because it actually provides an answer rather than cutting and pasting chemical giberish.

 

[Screwtop]

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

Maybe if you are a bomb disposal tech ... wondering whether to cut the blue or the red wire but this is just brewing beer isn't it?

If the tongue can guess the difference between say, 10IBU - surely that's a measurable acidity with simple equipment?

If 10g of X hop boiled for 60 minutes = 30IBU, and another Y = 15IBU ... what's the difference in AA%? I'm thinking X = 2Y.

I like Brewer Pete's method more because it actually provides an answer rather than cutting and pasting chemical giberish.

Well you tried Mark :lol:

 

[Wardhog]

Count backwards from 10 while chewing a hop cone. The AA% is the number you reach before you can't take it any more and spit it out.

 

[Screwtop]

Count backwards from 10 while chewing a hop cone. The AA% is the number you reach before you can't take it any more and spit it out.

And we have a winner :lol: :lol:

 

[bconnery]

Count backwards from 10 while chewing a hop cone. The AA% is the number you reach before you can't take it any more and spit it out.

So if it's 15% alpha you should spit 5 seconds before and then not bother putting the hops in your mouth?

 

[Nick JD]

If you boil 5g of 3% AA hops for 60 minutes in 300ml ... and 5g of 12% AA hops in 300ml for 60 minutes and drop a pH meter in the solutions, you'll get a different pH due to one solution having roughly three times as much isomerized AA.

Now you know how the pH relates to a known hop varieties you can extrapolate reasonably accurately what your back yard hop's AA is.

Why would this not work? Will the two solutions have identical pH values? Is the tongue able to discern levels of bitterness that don't relate to levels of isomerized AA's pH values?

 

[drsmurto]

If you boil 5g of 3% AA hops for 60 minutes in 300ml ... and 5g of 12% AA hops in 300ml for 60 minutes and drop a pH meter in the solutions, you'll get a different pH due to one solution having roughly three times as much isomerized AA.

Now you know how the pH relates to a known hop varieties you can extrapolate reasonably accurately what your back yard hop's AA is.

Why would this not work? Will the two solutions have identical pH values? Is the tongue able to discern levels of bitterness that don't relate to levels of isomerized AA's pH values?

As Mark has stated, measuring differences in pH is very difficult for very weak organic acids like the alpha acids in hops. Even in very concentrated solutions you wouldn't expect to see any differences. Not too mention the presence of beta acids as well as any compound capable of donating a proton.

Bitterness is very different to pH - the two are barely related so just because you can taste the difference between 2 hop teas doesn't mean there will be a pH difference.

Try making up 2 cups of black tea using 2 different types of teabags (tea leaves, not hops). Can you distinguish the difference in the bitterness? Does that relate to the acid levels of compounds in the teal leaves? Is there a difference in the pH?

 

[Effect]

Needed:

o 28 grams home grown hops (28.3 grams if you have accurate scales)
o sugar
o water measure in mL


Accurately measure:
28.3 grams of your home grown hops.
473 mL of water


Steps to make hop tea:
Boil the water for 15 minutes with 1 accurately measured tablespoon of sugar added.
Add your home grown hops and boil for 10 additional minutes.
Strain out the hops leaving you with hop tea.


Method to estimate alpha acid bitterness levels:
Mix 59mL of your hop tea with with 59mL of water.
Sip.
Taste bitter?
Mark a 1 on a piece of paper.
Take 59mL of this diluted mixture into a new cup and add 59mL additional water.
Sip again.
Taste bitter?
Mark another 1 on the piece of paper.
Take 59mL of this new diluted mixture into a new cup and add another 59mL of additional water.
Sip.
Taste bitter?
Mark another 1 on the paper.

Continue until you no longer taste bitterness.

Add up all the ones to get a final number.

That is your ballpark figure to brew with as %AA in your recipes.


Cheers,
Brewer Pete

That's the way they measure how hot a chilli is... the Scoville Scale

Cheers
Phil

 

[Nick JD]

As Mark has stated, measuring differences in pH is very difficult for very weak organic acids like the alpha acids in hops. Even in very concentrated solutions you wouldn't expect to see any differences. Not too mention the presence of beta acids as well as any compound capable of donating a proton.

Bitterness is very different to pH - the two are barely related so just because you can taste the difference between 2 hop teas doesn't mean there will be a pH difference.

Try making up 2 cups of black tea using 2 different types of teabags (tea leaves, not hops). Can you distinguish the difference in the bitterness? Does that relate to the acid levels of compounds in the teal leaves? Is there a difference in the pH?

So you're saying that two strong solutions of distilled water and 5g of the extract of 60 minutes water boiling of a 3% AA and a 12% AA will have the same pH?

All of the bittering compounds are acidic (albeit weak) and yet the pH remains the same? Or are you saying you'd need a very accurate pH meter but there would be a difference?

Are you just assuming this - or have you measured it?

I fully understand that AAs are weak acids ... but they would lower the pH by some degree. This degree would be relative to the concentrations of acids in the hops.

I'm by no means saying that this is a method to determine the absolute AA% of hops - but a relative measurement.

I would argue that a common-garden pH meter with an accuracy of 0.01-0.02 pH units will detect a difference between a solution of 3% vs a 12% one. It could be easily tested.

I thought the "bitterness" of tea was actually astringency?

 

[drsmurto]

So you're saying that two strong solutions of distilled water and 5g of the extract of 60 minutes water boiling of a 3% AA and a 12% AA will have the same pH?

All of the bittering compounds are acidic (albeit weak) and yet the pH remains the same? Or are you saying you'd need a very accurate pH meter but there would be a difference?

Are you just assuming this - or have you measured it?

I fully understand that AAs are weak acids ... but they would lower the pH by some degree. This degree would be relative to the concentrations of acids in the hops.

I'm by no means saying that this is a method to determine the absolute AA% of hops - but a relative measurement.

I would argue that a common-garden pH meter with an accuracy of 0.01-0.02 pH units will detect a difference between a solution of 3% vs a 12% one. It could be easily tested.

You are getting a little confused Nick about what you are actually arguing about - after a 60 minute boil you will be measuring the pH of iso-alpha acids, not alpha acids.

The OP want to determine the alpha acid level.

A pH meter with the detection and error specs you refer to might be able to detect a difference between a 3% AA and a 12% AA.

If you did detect a difference of 0.01 exactly what can you conclude from that?

 

[Nick JD]

You are getting a little confused Nick about what you are actually arguing about - after a 60 minute boil you will be measuring the pH of iso-alpha acids, not alpha acids.

The OP want to determine the alpha acid level.

A pH meter with the detection and error specs you refer to might be able to detect a difference between a 3% AA and a 12% AA.

If you did detect a difference of 0.01 exactly what can you conclude from that?

Okay - we're getting somewhere. Of course I'm talking about the isomerized AAs - how many times have I used the word "boil"?

There's a correlation between AA% and isomerized AA%. That's freakin' obvious. Higher percentages of AAs mean larger amounts of isomerized AAs in the wort.

Let's say the solution made with 3% AA hops has a pH of (I'm guessing here - I haven't yet done the experiment) 4.58; and the 12% AA solution 4.48 (again, these are just numbers to show the working, not real numbers).

That's a 0.10 pH difference.

If we do the same boil with a 7.5% AA hop and get a pH of 4.53 ... well then we've got something.

Some chap who grows his own hops can boil up the same solution, get a pH of 4.50 and know he's got roughly 4.5% AA hops.

If it doesn't work then it doesn't work - but let's not disregard it by guesswork. A you've said: "A pH meter with the detection and error specs you refer to might be able to detect a difference between a 3% AA and a 12% AA."

 

[drsmurto]

Okay - we're getting somewhere. Of course I'm talking about the isomerized AAs - how many times have I used the word "boil"?

There's a correlation between AA% and isomerized AA%. That's freakin' obvious. Higher percentages of AAs mean larger amounts of isomerized AAs in the wort.

Let's say the solution made with 3% AA hops has a pH of (I'm guessing here - I haven't yet done the experiment) 4.58; and the 12% AA solution 4.48 (again, these are just numbers to show the working, not real numbers).

That's a 0.10 pH difference.

If we do the same boil with a 7.5% AA hop and get a pH of 4.53 ... well then we've got something.

Some chap who grows his own hops can boil up the same solution, get a pH of 4.50 and know he's got roughly 4.5% AA hops.

If it doesn't work then it doesn't work - but let's not disregard it by guesswork. A you've said: "A pH meter with the detection and error specs you refer to might be able to detect a difference between a 3% AA and a 12% AA."

You are assuming the pH scale is a linear one.

It's not, it's a logarithmic scale.

You would need a lot more than 2 points to being able to plot a graph that would enable you to predict AA based on pH based on your current hypothesis.

But..... on paper it just might work.

Bugger, i just agreed with you. :blink:

As long as someone is willing to trial a range of hops with %AA from 2 through to 15 or so covering almost every AA unit then you could come up with a graph that may make everyone else's life easier.

I nominate you for the job Nick!

 

[Wolfy]

As long as someone is willing to trial a range of hops with %AA from 2 through to 15 or so covering almost every AA unit then you could come up with a graph that may make everyone else's life easier.

Interesting idea, but would it actually be any use?
I'd have thought that experimental/local error would be more significant than any changes in pH that you could measure accurately with a home-setup-pH-meter.
Just for a start with such small volumes the evaporation rate alone would be variable and individual, etc etc.