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Estimating bitterness: Algorithms and state of the art

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SumnerH

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So I figured this is the correct forum for a discussion of various bittering algorithms and what we know about IBUs. I'm going to kick off with a few topics

1. Brief history and state of the art on what IBUs are and how hops contribute to them, mainly cribbed from John Palmer's interview on BBR regarding the 2007 International Brewer's Symposium on Hop Flavor and Aroma.
2. A run-down of the results of BBR's shoot-out comparing 5 major IBU estimation algorithms with actual IBU measurements.
3. A run-down of the major homebrew bittering calculations. As of this moment I've got full information on:
  1. Rager
  2. Garetz
  3. Tinseth

Obviously, at least Mosher and Daniels would be good to add here.
4. A discussion of the issues involved with partial-boil bittering calculations
5. A discussion of issues involved in designing a more accurate bittering algorithm, especially in light of information from (1) and (2).

I'll edit this post as a sort of table of contents for the thread.
 
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SumnerH

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First, a run-down of what IBUs are and what we know about them from John Palmer's interview on BBR regarding the 2007 International Brewer's Symposium on Hop Flavor and Aroma 2007.

First, IBUs are _not_ mg of isomerized alpha acid/1 ml of beer. That's a commonly-given definition (including in Palmer's own how to brew), but it's not right. IBUs take a measurement of the acids in beer and run it through a formula designed to align with empirical bitterness data. That measurement includes not only isoalphas (humulone, cohumulone, adhumulone) but also oxidized beta acids (lupulone, colupulone, adlupulone).

This is important in a few ways. First, the character of the bitterness contributed by betas is different from that contributed by alphas. It's usually described as "softer" or "less sharp" while being equally bitter.

That leads in to a discussion of aged hops. Beta acids are not, by themselves, bitter, but the oxidized forms are. So beta bitterness increases as hops age. Alphas are the opposite, meaning that alpha acids tend to decline as the hops age.

Now, most hops have in the range of 4-6% betas. That means that older hops varieties (your noble hops, east kent goldings, cascade, cluster, etc) aren't all that far off from a 1:1 alpha:beta ratio. As they age, they won't lose that much bittering capability--but the _character_ of that bittering will shift toward the beta kind.

Indeed, Palmer mentioned a test that measured 2 beers of 22 IBUs, one made with fresh hops and the other with aged hops. The former had 23.5 ppm of isoalphas. The latter had just 3.5 ppm. So it's potentially a massive flavor difference at the same level of IBUs. Palmer notes that if you're making historic styles of beer this could be very important, as shipping hops was slow and it was not uncommon to use hops over a year old in brewing (especially in the US).

Also, there's the matter of newer high-alpha hop strains. Things like Columbus, Sterling, etc generally have closer to a 2:1 or 3:1 alpha:beta ratio. That means that when _they_ age, they not only mellow in the character of bitterness but they also lose actual bittering capabilities much faster than more balanced alpha/beta hops. That's might be worth keeping in mind if anyone decides to do American lambics or some other beer with intentionally aged hops.

Okay, so that's the betas.

Now, some other results:
1. The rate at which alpha acids isomerize is pretty constant in worts of various densities. That is, the gravity of your wort has almost zero impact on how much hop utilization you get. But:
2. Isoalphas cling to everything, including hot break. So there's an indirect effect where higher-gravity boils are likely to lose more isoalphas in their (correspondingly greater) hot break material.

This is interesting in practice. It explains why the bittering algorithms that use a gravity correction can be in the right ballpark (the gravity factor is a stand-in for amount of break generated). However, it also suggests that you should not include simple sugars in the gravity calculations for the purposes of figuring out IBUs. It also suggests that extract (which has already beenn boiled, and lost a fair bit of break) may result in somewhat higher real bitterness than you'd otherwise expect, since an extract brew at the same gravity will lose less bitterness than an all-grain to break. Finally, it suggests that wheat and rye (which generate a lot more proteins than barley) might need to be weighted much more heavily in terms of gravity to account for the extra isoalphas that drop out in their break.

Those were the major points I pulled from Palmer's interview.
 

Kaiser

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It's important to put the bitterness estimation problem into perspective as being mostly driven by home brewers. All these tables actually come from home brewers and I have not come across such tables in technical brewing literature.

This leads me to believe that this is not a problem that many commercial brewers deal with. They simply estimate the IBUs that they will get, brew a pilot batch, measure IBUs and adjust from there.

The problem with estimating IBUs is that there are a number of unknown or unaccounted for factors:

- boil pH
- hop age
- loss of bitterness in kraeusen
- loss of bitterness in the yest trub

As a result I'm not estimating my IBUs using these formulas anymore. I simply use guidance from previous batches. But if you are just starting out to gather experience and/or brew a lot of beers these formulas are just fine. Just pick one and stick with it and get an idea how bitter a beer with an "IBU" level estimated by that formula tastes to you. If you estimated 30 IBU and it tastes less more than you expected, b/c you had commercial beers that measured 30 IBU, aim for 35-40 IBU next time. And don't get hung up tweaking the IBUs to less than +/- 1 or less.

For the Tinseth numbers I know that he measured them post boil. Although about 30% of the IBUs after the boil will be lost in fermentation his estimation is surprisingly accurate when it was compared with actually measured IBUs.

Kai
 
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SumnerH

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It's important to put the bitterness estimation problem into perspective as being mostly driven by home brewers. All these tables actually come from home brewers and I have not come across such tables in technical brewing literature.

This leads me to believe that this is not a problem that many commercial brewers deal with. They simply estimate the IBUs that they will get, brew a pilot batch, measure IBUs and adjust from there.

The problem with estimating IBUs is that there are a number of unknown or unaccounted for factors:

- boil pH
- hop age
- loss of bitterness in kraeusen
- loss of bitterness in the yest trub

As a result I'm not estimating my IBUs using these formulas anymore. I simply use guidance from previous batches. But if you are just starting out to gather experience and/or brew a lot of beers these formulas are just fine. Just pick one and stick with it and get an idea how bitter a beer with an "IBU" level estimated by that formula tastes to you. If you estimated 30 IBU and it tastes less more than you expected, b/c you had commercial beers that measured 30 IBU, aim for 35-40 IBU next time. And don't get hung up tweaking the IBUs to less than +/- 1 or less.
Yeah, within 5 is close enough. The problem is (as we'll see when I post the results from the BBR show) that you'll wind up with cases where Garetz is giving you an estimated 10 IBUs, Tinseth is giving 39, and Daniels is giving 64.

In general, if you're just developing recipes for yourself iteratively, you don't need accurate IBUs. And you're definitely better off just picking one algorithm and sticking with it so you know about how things taste on that scale.

The problem is if you're trying to actually meet IBU levels, either to meet style guidelines for competition or to clone commercial beers with known IBUs. Having a more accurate algorithm for estimating target IBUs would be nice, there.

For the Tinseth numbers I know that he measured them post boil. Although about 30% of the IBUs after the boil will be lost in fermentation his estimation is surprisingly accurate when it was compared with actually measured IBUs.
I'll be putting up some measurements later on comparing 5 algorithms' estimates with the actual IBUs (BBR did the test a couple years back).
 

Kaiser

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The problem is if you're trying to actually meet IBU levels, either to meet style guidelines for competition or to clone commercial beers with known IBUs. Having a more accurate algorithm for estimating target IBUs would be nice, there.

Even for competition the judging is based on bitterness perception and not actual IBUs. If you don’t really know how bitter a given style should taste then you don’t know much about that style to begin with.

But yes it would be nice to estimate the IBUs more correctly, but that is actually a quite complex problem and I doubt that it will be solved anytime soon. It would take a lot of experimentation to come up with a model that can include pH and fermentation effects.

Kai
 
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SumnerH

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Even for competition the judging is based on bitterness perception and not actual IBUs. If you don’t really know how bitter a given style should taste then you don’t know much about that style to begin with.
Absolutely.
But yes it would be nice to estimate the IBUs more correctly, but that is actually a quite complex problem and I doubt that it will be solved anytime soon. It would take a lot of experimentation to come up with a model that can include pH and fermentation effects.
Yep. I don't think that anything incredibly accurate is likely, but I think there are some corner cases that can be improved to come up with something that's generally within about 5 or so IBUs.
 
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SumnerH

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IBU testing results from BBR

BBR ran a show testing several different beers with various IBU estimating algorithms and then measuring the actual IBUs. They didn't always specify fully what the boil size was, the OG, or the entire hopping schedule but they often did. For each beer, I'll list the name, any notes they mentioned on the recipe, the Average IBU estimate from all 5 algorithms, the standard deviation, and then the IBUs estimated by each algorithm and the actual measured IBUs.

Mark's Hefeweizen:
Extract, 1 oz Tettnang 4.5% @60mins
Avg: 15
StdD: 2
Rager: 17
Garetz 12 (always lowest)
Mosher 14
Tinseth 15
Daniels 17 (always highest)
Actual: 7

Belgian Brunette
Both added at 60 min: .5oz Styrian Goldings 6% and .85oz Hallertau 5.3%
Avg: 26
StD: 4
R: 30
G: 22
M: 23
T: 23
D: 30
Actual: 18
Beer was 6 months old when measured

Vanilla Porter
Various unspecified hops at 60min, 15 min, 5 min
Avg: 24
StD: 4.9
R: 27
G: 18
M: 23
T: 22
D: 31
Actual: 27

6pack Simcoe
15, 5 mins, flameout, dry-hop
Avg: 41
StD: 17.5
R: 37
G: 15
M: 42
T: 48
D: 63
Actual: 34

Late-hop Simcoe
Malt extract
Some confusion over boil; the calcs are for 10.1 minute boil, but it was actually a 15 minute boil. Numbers in parenthesis are from re-running the algorithm with the proper 15 minute boil length. I have no idea how they treated the 15 minute addition when running with the erroneous 10.1 minute boil, I'm presuming they treated it as a 10.1 minute addition.
2.5 oz @15min, 1 @5, .5 @flameout, 1 oz Amarillo dry-hop
Avg: 38
StD: 19
R: 37
G: 10 (18)
M: 38
T: 39
D: 64 (74)
Actual: 34

IPA
10 gal
18 oz cascade
2 @90 60 30 25 20 15 10 5 1
Avg: 85
StD: 21
R: 91
G: 57
M: 83
T: 78
D: 116
Actual: 77
 
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SumnerH

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Here are the current hops utilization formulae that I have specs for.

For all of these the same inputs are used:
"minutes" is a number of minutes this hop is in the boil
"gravity" is a decimal-point specific gravity (e.g. "1.050")
"aa" is the alpha-acid content of the hops as a decimal (e.g 7.5% is "0.075")
"volume" is a decimal in liters (e.g. 5 gallons is "18.927").
"g" is a weight of the hops in grams (e.g. 1 oz is "28.35")

First, Rager. It definies hops utilization as a function of the number of minutes. tanh is a standard hyperbolic tangent function.

Then it defines a gravity-correction factor (here called "ga"), which is (gravity-1.050)/.2 if the gravity is over 1.050, or 0 if the gravity is 1.050 or lower.

Finally, it calculates the IBUs using these numbers:

Code:
def utilization(minutes):
    return (18.11+13.86*tanh((minutes-32.32)/18.27))*0.01

def ga(gravity):
    if gravity>1.050:
        return 0
    return (gravity-1.050)/.2

def ibu(g, minutes, aa, volume, gravity):
    """g: grams of hops"""
    return (g*utilization(minutes)*aa*1000)/(volume*(1+ga(gravity)))
Next, Tinseth.

Tinseth defines utilization as the product of a "bigness" factor (dependent on the gravity of the boil) and a "btf" factor (dependent on the length of the boil). It then defines IBUs as the utilization times the milligrams per liter of alpha acids.

Code:
# Note: pow(x, y) is "x to the y power".
# e here is the mathematical constant e, approximately 2.71828...
def bigness(gravity):
    return 1.65*pow(0.000125, (gravity-1))

def btf(minutes):
    return (1-pow(e, (-0.04 *minutes)))/4.15

def utilization(minutes, gravity):
    return btf(minutes)*bigness(gravity)

def mgl_aa(g, aa, volume):
    return (aa*g*1000)/volume

def ibu(g, minutes, aa, volume, gravity):
    return utilization(minutes, gravity) * mgl_aa(g, aa, volume)
Finally, Garetz. Garetz is a bit trickier since it requires on a large table lookup for utilization. I'll list it here, but I use a formula to get close results instead:

Code:
def chart_utilization(minutes):
    if minutes <= 0:
        return 0
    elif minutes <= 15:
        return 2
    elif minutes <= 20:
        return 5
    elif minutes <= 25:
        return 8
    elif minutes <= 30:
        return 11
    elif minutes <= 35:
        return 14
    elif minutes <= 40:
        return 16
    elif minutes <= 45:
        return 18
    elif minutes <= 50:
        return 19
    elif minutes <= 60:
        return 20
    elif minutes <= 70:
        return 21
    elif minutes <= 80:
        return 22
    else:
        return 23
If you do a curve fit, you can create a mathematical function that gives a very close result to the table lookup without discontinuities:

Code:
co_a = 2.5251990477100890E+01
co_b = 2.2060400680981388E+01
co_c = 3.3792756276592284E+00
co_d = 5.0643078483394244E-01
def utilization(x):
    return co_a * (1.0 - pow(1.0+pow(x/co_b, co_c), -1.0*co_d))
Whichever method you want, it just gets more complicated from there There are a number of small factors calculated along the way, and then the very broadest level of the algorithm is an iterative process where you make a guess at the final IBUs (called "d_ibu" for desired IBUs), run the equations, and then if the answer isn't close to the guess you try again with a d_ibu closer to the answer you got:

Code:
def calc_ca(final_volume, boil_volume, gravity, d_ibu, elevation=0):
    cf = final_volume/boil_volume
    boil_gravity = cf*(gravity - 1) + 1
    gf = (boil_gravity - 1.050)/.2 + 1
    hf = (cf*d_ibu)/260 + 1

    tf = (elevation/550)*.02 + 1

    return gf*hf*tf

def ibu(g, minutes, aa, volume, gravity, boil_volume, elevation):
    aa = 100 * aa
    d_ibu = 50
    calc_ibu = 0

    # abs(x) means "the absolute value of x"
    while abs(d_ibu-calc_ibu)>0.1:
        correction = (d_ibu - calc_ibu)/5
        d_ibu -= correction
        ca = calc_ca(volume, boil_volume, gravity, d_ibu, elevation)
        calc_ibu = (utilization(minutes)*aa*g*0.1)/(volume*ca)
    return calc_ibu
As you can see, Garetz also takes elevation and boil volume into account.


For any readers who are programmers, note that the above is all well-formed Python code. If you head it up with the following:
Code:
from math import tanh, e, pow, log
you should be able to include any of those algorithms directly in your python program.
 

StoutFan

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Now, would this take FWH and dry hopping into effect also, or am I off base here?
 
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SumnerH

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Now, would this take FWH and dry hopping into effect also, or am I off base here?
None of these do.

I'd guess that a FWH that then goes into the boil could be treated as a beginning-of-boil addition (or, better, a 90 minute addition even if you're doing a 60 minute boil) and ought to get close*, since utilization past 60 minutes increases very slowly, but I'd appreciate more thoughts on that. http://brewery.org/library/1stwort.html has some interesting FWH notes.

If you treat dry-hopping as a 0-minute addition, it's going to contribute nothing except by Rager where it'll have 5% utilization. I'm really not sure how to deal with it. I know dry-hopping is usually much more for aroma than bittering, but I don't know if _no_ bittering is appropriate. Thoughts?

*Assuming at least 60 minute boils
 

StoutFan

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Well, with alpha acids probably not being effected in the fermenter, would the residual bitterness from oxidizing beta acids add to the bitterness, although not by much?
 

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Well, with alpha acids probably not being effected in the fermenter, would the residual bitterness from oxidizing beta acids add to the bitterness, although not by much?
From "Brewing Science and Practice"

Probably the most important oxidation products of the beta-acids are the hulupones obtained by autoxidation...The hulupones are reported to be twice as bitter as the iso-alpha-acids; they are not found in green hops but accumulate during storage when concentrations of 3% have been reported...They are also formed in wort boiling and survive into beer (several ppm). They may be more important in stout brewing when hops are boiled with wort more than once. After the first boil, the resins that have not dissolved will be spread over the surface of the spent hops making them accessible to autoxidation between boils...With regard to bitterness of hulupones, Verzele and De Keukeleire (1991, p. 377) report that beers bittered only with pure hulupone (100 mg/l) were undrinkable but beers with 100 IBU derived from iso-alpha-acids are also likely to be unacceptable.
You have to consider, however, that fermentation occurs under an anaerobic environment, therefore any bitterness from oxidizing beta acids would have to compete with the yeast scavenging O2 during lag-phase growth. Nonetheless, it's all the more reason to siphon "quietly."
 
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SumnerH

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John Palmer Brew Your Own article containing much of the same information from the podcast I linked earlier:
Brew Your Own: The How-To Homebrew Beer Magazine - Recipes - Behind the IBU: Advanced Brewing

One of the papers, on aging hops. I'll try to read this, digest it, and post a writeup unless someone else gets to it before me...
http://www.hopsteiner.com/pdf/Kaltner_Text_proceedings_Hop_ Symposium_Corvallis.pdf
Some quick-shot blurbs about some of the talks:
http://www.barthhaasgroup.com/cmsdk/content/bhg/research/hopscience_newsletter/hs_vol08_2007.pdf

Confirmation of the "gravity doesn't affect hops utilization", from a 1989(!!) American Society of Brewing Chemists journal:
ASBC Journal 1989 - Hop Utilization in the Brewery-An Interbrewery Comparison.
" In the range 10.5-13.5° P, no relationship between hop utilization and original gravity was found."
 

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As a purely empirical data point, I recently did up a bunch of SMaSH experiments with 1.050 Maris Otter wort and 40 IBUs (Rager) each with Perle, Sterling, Fuggle, Northern Brewer, Cascade, and Amarillo. S-05 was the yeast. The perceived bitterness differences between these beers couldn't have been more dramatic. Homebrewers who think they can craft a beer by numbers alone are seriously kidding themselves.

I also gained a serious respect for Perle from these tastings; what a wonderful hop. :rockin:
 
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SumnerH

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As a purely empirical data point, I recently did up a bunch of SMaSH experiments with 1.050 Maris Otter wort and 40 IBUs (Rager) each with Perle, Sterling, Fuggle, Northern Brewer, Cascade, and Amarillo. S-05 was the yeast. The perceived bitterness differences between these beers couldn't have been more dramatic.
Do you mind posting your perceptions of each, if you can remember them?
 

jkarp

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Do you mind posting your perceptions of each, if you can remember them?

Sure. My goal was to refine my palate to the overall characteristics of each hop, so there's other ramblings besides perceived bitterness but anyway...

Fuggle: Head a little weak, nice aroma, but it surprisingly seems under-hopped, even at 40 IBU. Can definitely see why Fuggle is so popular in English beers. Earthy flavor with a hint of pepper. It's definitely not an "in your face" hop however, and therefore the malt flavor clearly stands out.

Sterling: Blah. That's right. Blah. Like Fuggle, at 40 IBU, it still seems badly under-hopped. It does have a very nice aroma, but the flavor is an underwhelming light earthy / spice. Frankly, I'm floored. Being a certified Belgian nut, I've made more beers with Sterling than any other hop. GREAT beers. I'm frankly floored that it makes a poor SMaSH hop.

Perle: I've got very little brewing experience with this hop, and it was clearly the shocker of this batch. From the very first sniff to the bottom of the glass, I thought, OH MY GOD, I'VE MADE CORONA! Now this isn't a bad thing by any stretch - Corona happens to be a guilty pleasure, I'm ashamed to say. I'm just shocked that a German hop and an English malt, brewed as an ale, could be such a dead-ringer for a Mexican lager! Beer was crystal-clear - clearest of the bunch. Hop taste was spicy with just a hint of mint and faded rapidly on the tongue leaving a nice malt finish. I've stumbled onto a perfectly balanced brew here and a full-sized batch of this just went to the top of the must brew list.

Amarillo: Massive frothy head; powerful, pungent aroma. Amarillo is SUCH a fun hop. It's often compared to the "C" hops, but I tend to disagree. There's something distinctively different in their taste I can't put my finger on. Need to do a side-by-side compare with Cascade to further nail it down. Amarillo does leave quite a bit of haze in the beer compared to the others. An Amarillo IPA is definitely going on the to-do list...

Northern Brewer: This hop is getting quite scarce. Glad I've still got a half pound as it's definitely interesting. Somewhat similar to Perle, NB packs a healthy bittering punch, but there's more floral notes going on. Absolutely makes a fine SMaSH beer - I wouldn't hesitate brewing this one again, exactly as-is.

Cascade: Every mainstream American beer came to mind the very moment I opened the bottle. This SMaSH is Budweiser with actual flavor. So, the difference between Cascade and Amarillo? Seems easy now. Cascade is more spicy, Amarillo is more floral. Bittering seems equal between the two. I definitely like Amarillo better.

Gratuitous SMaSH pour pic (Cascade):

beer45.jpg
 

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Well, I guess that IBU ratings are perceived differently to different people. With each hop acting different at 40 IBU's, this throws a wrench in the works for calculation. (and my vote is for your Amarillo IPA, sounds tasty):)
 

pjj2ba

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As a purely empirical data point, I recently did up a bunch of SMaSH experiments with 1.050 Maris Otter wort and 40 IBUs (Rager) each with Perle, Sterling, Fuggle, Northern Brewer, Cascade, and Amarillo. S-05 was the yeast. The perceived bitterness differences between these beers couldn't have been more dramatic. Homebrewers who think they can craft a beer by numbers alone are seriously kidding themselves.

I also gained a serious respect for Perle from these tastings; what a wonderful hop. :rockin:
I'm assuming though that you used these hops for more than just a 60 min. addition. I believe the late additions, particularly if larger amounts of hop were used, will have a significant impact on the perceived bitterness (lowering it). I'm talking strictly bittering here, not flavor and aroma. I'm convinced that what bittering compounds that are released/isomerized from late hop additions (20 min. and less) are different from those that have had the benefit of 60 mins. of boiling. I like to keep track of the IBU's individually, per addition, and not to add them up. ie. I want X IBU's at 60', and Y IBU's at 20', and I don't bother with 5 min. or later. I don't think Z IBUs from a 60 min. addition with taste the same as Z IBUs that is 2/3 from 60' and 1/3 from 20'. I base my 20 min. addition of the flavor I want from those hops, not how many IBU's it will give me.

I've got a lager series I'm in the middle of brewing, not quite a SMASH, but all have the same grain bill, same bittering hop (magnum @ 60 min.) with different hops (one per brew) at 20 min. (1/2 oz) and 5 min. (1/4 oz). I'm very interested to see how the Sterling turns out in term of bitterness as it's alpha acid content was twice that of the other hops I've used. We'll see if the sterling version has a higher percieved bitterness.

+1 on Perle
 

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All were done with 30 minute variable and 10 minute fixed hop additions; the 30 minute quantity being adjusted to meet 40 IBUs, of course. My reasoning was, 10 and 30 min are the crossover points of aroma/flavor and flavor/bittering utilizations. That way hopefully some of each characteristic would be represented in the final beers.
 
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I'm going to add this first hand account of a commercial brewery attempting to get lab tested IBU levels vs their calculations.

http://www.deschutesbrewery.com/blog/2009/02/13/lies-damn-lies-and-statistics/

But 95 IBU&#8217;s turned out to be so much wishing. Our first brewing of Hop Henge this year produced the following result. The very vigorous ferment, with a fermenter at capacity, blew our precious dry hops all over the floor depriving us of all the goodness therein. The result was a beer we calculated to, on paper, 243 IBUs! In the bottle, we only got 80 IBUs. Still, as I mentioned earlier, you apparently loved it. So, what did we do? We made another batch, added more hops, only filled the fermenter half-full and thought we would blow the doors off the beer (and your taste buds). The original calc&#8217;s on batch #2 were the same as batch #1, but without the blow-off on the floor we ended up with a massive 117 IBUs in the fermenter, as determined in our lab this time. We were excited at the possibilities and fastened our seat belts for the ride. The beer has now been centrifuged and removed from the dry hops (which then took our guys and gals 4 hours to remove from the fermenter!) and we sent it back to the lab for analysis looking to tell you of our herculean feat. Meanwhile we tasted the two batches side by side today and were impressed by the huge pucker-factor in the new Henge, much greater than batch #1. So, we sent it off to the lab to await the results. 87 IBUs! We still did not even hit our promised 95 IBUs.
 

pjj2ba

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All were done with 30 minute variable and 10 minute fixed hop additions; the 30 minute quantity being adjusted to meet 40 IBUs, of course. My reasoning was, 10 and 30 min are the crossover points of aroma/flavor and flavor/bittering utilizations. That way hopefully some of each characteristic would be represented in the final beers.
This makes sense then. I think the more you boil the hops, the more you loose the individual characteristics. For my lager series, I'm looking for differences inflavor and aroma, with the bittering being held constant (hopefully).
 

jkarp

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It's fascinating stuff to play with, that's for sure. Looking forward to hearing your results pjj2ba.
 

ssabin

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Well, it's obvious that there is a lot going on and that accurately predicting IBUs is difficult at best at this point in time. Still, I was curious as to which IBU predictor model was "best".

It would be nice to simply cut and paste the data I used behind these summaries, but that's not so easy to do here and keep the formatting (column alignment).

So to summarize, my take on the data:
1) there are a lot of holes in understanding how the data was obtained, what assumptions were made, what process was followed, etc.
2) there is a definite pecking order of algorithms in terms of accuracy at predicting IBUs in the final brew.
3) The top 3 algorithms are likely in a similar range of acceptability, while the worst seems to have a flawed model.

The results:

1. Mosher
Chi-squared statistic (lower is better, and is equal to sum of (Oi-Ai)^2/Ai where Oi is observation i, and Ai is actual value i): 11.8
Std Dev of Chi-square data (lower is better): 2.53
Average Error value (closer to zero is better): 4.33 IBU's (over-predicted)
Std Dev of errors (lower is better): 4.32 IBUs
Worst error (lower is better): 8 IBUs (over-predicted)

2. Tinseth
Chi-squared: 17.97
Std Dev of Chi-sq data: 3.64
Avg Error: 4.67 IBUs (over-predicted)
Std Dev of errors: 6.41 IBUs
Worst error: 14 IBUs (over-predicted)

3. Rager
Chisquared statistic: 25.36
Std Dev of Chi-squared data: 5.79
Avg Error: 7.00 IBUs (over-predicted)
Std Dev of errors: 5.73 IBUs
Worst error: 14 IBUs (over-predicted)

4. Garetz
Chisquared statistic: 30.8
Std Dev of chisquared data: 3.49
Avg Error: -9.17 IBUs (under-predicted)
Std Dev of Errors: 11.27 IBUs
Worst Error: 20 IBUs (under-predicted)

5. Daniels
Chisquared statistic: 114.43
Std Dev of chisquared data: 16.14
Avg Error: 22.33 IBUs (over-predicted)
Std Dev of errors: 15.68
Worst Error: 40 IBUs (over-predicted)

I also notice that a single data point (the 6 Simcoe) sticks out in the Tinseth model, meaning there might have been some issue with the process that wasn't captured in the prediction for that particular batch. At any rate, I think that based on this limited amoutn of data, the top 3 algorithms perform well enough to be useful.
 

SpanishCastleAle

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What is the Mosher algorithm?

I used Daniel's method in my homebrew spreadsheet...no wonder I rely more on 'feel' than anything wrt hops. I trust my color prediction more than my bitterness prediction.

I'm gonna try Tinseth first and see how that goes but I'd like to try all of them...but I didn't see the Mosher method.
 
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SumnerH

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I haven't written up Mosher or Daniels yet. I'll probably skip Daniels since it's not particularly accurate, but I'll get around to Mosher eventually.
 

SpanishCastleAle

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I just need the equation so I can put it in a spreadsheet. I converted the algorithms you posted earlier back to a 'regular' equation so I can use them. Either will do.:)

My last programming was a Fortran class in the late 80's...never really used it and can't remember much of it. So I just use a spreadsheet.:eek:
 

ssabin

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You've inspired me, DEC, to see if the average, or some combination of the top 3 algorithms provides an even "better" algorithm. But I won't be able to look at this until tomorrow.

For the record, I also use Tinseth in my spreadsheet. I won't change unless I can markedly improve the quality of the prediction.
 

Homercidal

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Homebrewers who think they can craft a beer by numbers alone are seriously kidding themselves.

I also gained a serious respect for Perle from these tastings; what a wonderful hop. :rockin:
I agree. I could never figure out how they get this to work. Seems impossible to determine exactly how much bitterness you will get with all of the variables inherent in the whole process.
 
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SumnerH

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Confirmation that utilization is independent of wort gravity:
BBR conducted actual measurements of the IBUs in 3 beers, one with a boil gravity of 1.127, one with late extract addition for a boil grav of 1.077, and one with a full boil at 1.068.

The same hopping schedule was used for all 3, and hop utilization is identical for all 3; the March 4, 2010 - BYO-BBR Experiment III:
http://www.basicbrewing.com/index.php?page=radio

(it also confirms that late addition can help make a lighter beer, though the effect is small).
 
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I recently boiled some hops in water in the microwave in order to boost the ibu's of a batch, Seems to have worked.

Wish there was an easy way to measure the IBU's of home grown hops. I had to guess and I guessed to high.
 
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