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Old 10-03-2009, 10:00 PM   #11
Edcculus
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Here is what wikipedia has to say about the molecular structures of different essential oils found in hops

Humulene
Myrcene
Caryophyllene
Farnesene

I believe we are only interested in humulene

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Old 10-03-2009, 11:43 PM   #12
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I'm no chemist, but this guy is: http://homebrewandchemistry.blogspot...chemistry.html

He has a diagram of a possible way in which the alpha acids are isomerized. I have no idea if he's right or wrong.

-Steve

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Old 10-03-2009, 11:51 PM   #13
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AH! that explains so very much about "alpha acids". That's pretty cool, good find! (I study organic chemistry...so that speaks to me :-)) thanks a lot!

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Old 01-07-2014, 02:35 AM   #14
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It's the isomerization that creates the bitterness-- converting one isomer of a hop acid into another. For a given amount of hop acids in the boil, the percentage that get isomerized is your utilization.

-Steve
Picking up on an old thread to understand the effect of isomerization. From what I read, the bitterness contribution to beer depends on boiling the hops so that the alpha acids are "isomerized" and the bitterness develops over time even though the alpha acids dissolve almost immediately.

I have tasted raw hops and they taste pretty bitter to me. Does the boiling then make the taste *more* bitter because the molecular structure has been altered?
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Old 01-07-2014, 12:23 PM   #15
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It isn't necessarily isomerization…it is dissolution that is the problem. Isomerized alpha acid have a low solubility in water. If you do partial boils, and then dilute up to 5 gallons, you are limiting the amount of solubilized iso-alpha acids in your final volume which directly relates to IBUs.

The IBU measurement IS the concentration of isomerized alpha acids. I forget what it is specifically but it is something like 1 IBU = 1mg/L of alpha acids. As people well know, there is a cap of IBU around ~100 give or take so 100 mg/L is the maximum solubility of alpha acids.

Here is a fun math experiment for everyone. The golden equation for dilutions is C1V1 = C2V2.

Lets say that you do a 1 gal boil and use 20 oz of hops at 60 minuts. Your max IBU for that 1 gallon is 100 lets say (what ever the cap is). What does your final (theoretical) IBU come out to when you dilute?

C1=100 IBU
V1 = 1 Gallon
C2 = ? IBU
V2 = 5 Gallon

C2 = C1*V1 / V2 = 100*1 / 5 = 20 IBU


One thing that I have thought about for a while is the isomerization. It is well known to happen over temps of 100C so if you are boiling water for an hour, you should be creating more than 100 IBUs worth of isomerized alpha acids. Where do the others go? They have to evaporate off. Anything that doesn't dissolve in the water will be an oil floating at the top of the wort and is most likely being evaporated off. This is probably important to note because it will really impact partial boils. You are most likely converting more than plenty of alpha acids over but you are in turn just boiling them off.

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Old 01-11-2014, 02:02 AM   #16
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Originally Posted by ColumbusAmongus View Post
One thing that I have thought about for a while is the isomerization. It is well known to happen over temps of 100C so if you are boiling water for an hour, you should be creating more than 100 IBUs worth of isomerized alpha acids. Where do the others go? They have to evaporate off. Anything that doesn't dissolve in the water will be an oil floating at the top of the wort and is most likely being evaporated off. This is probably important to note because it will really impact partial boils. You are most likely converting more than plenty of alpha acids over but you are in turn just boiling them off.

My understanding is that the conversion will slow as the max solubility is approached.
Another factor which plays into hop usage in a partial boils is that as you approach the 100 IBU limit, you need exponentially more hops to get another IBU.
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Old 01-18-2014, 12:33 PM   #17
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Any thoughts to what happens the other way?

Eg. suppose you manage to max out at the ~100IBU level and continue boiling so the wort volume decreases through evaporation. Then either solubilized iso-alpha acids remain in solution and break through the 100IBU barrier, or they start to precipitate to maintain the 100IBU barrier?

Hops for thought.

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