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Hop Isomerisation Temperatures

Discussion in 'General Brewing Techniques' started by losp, 12/10/12.

 

  1. losp

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    Posted 12/10/12
    Now, I know there has been a lot said about Hop Isomerisation times. Apologies if this topic has come up many times.

    But i am wondering if anyone has a graph or something like that showing the average isomerisation amount in relation to the temperature.
    I have been no chilling for some time and have noticed that my beers have been a little too bitter and a little too lacking in aroma.
    I have sinse read/realised that i the wort might be hot enough for quite some time to add bitterness/flavour and take away aroma. I feel stupid for not having realised this soon enough.

    I usually whirlpool for some time (i dunno lets say 10 minutes) and tap it to the cube. I have no idea what temperature it is by this stage, or how long it takes overall, nor have i tracked the temperature drops over time. If i had some figures relating to the Isomerisation amount at each temperature, i may be able to do something here.

    I boil in a 50L - 8mm thick stock pot outsite and no-chill in a blue Jerry can. As this is a very common setup, so i doubt my results would vary too much to what other people would experience.

    From what i have read online, it seems that the minimum temperature is around 75-80c (this is from memoery and is in no way accurate), i would imagine that there is a certain logarithmic curve from there on.

    Anyone?
     
  2. Rob S

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    Posted 12/10/12
    Can't help you but it seems we got the same setup - 50 L pot into blue jerry can.

    I was having the same problem.

    I'll be following this thread.

    As a general rule of thumb, I reduce the hop additions by 15 to 20 mins.

    15 min hops are done at flameout.

    Anything less is divided up into other steps like into the cube before transferring wort. Into the cube halfway through transfer and into be cube just before I put the lid on.

    All this depends on how much I've drunk by this stage.......YMMV.

    Although I'm sure you've researched & tried all of this yourself as have many many others on here.

    Works good for me but.
     
  3. felten

    Homebrew Conjecturist

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    Posted 12/10/12
    I don't think there has been any research on a formula for calculating isomerisation below 100c, because it's not that important in the industry. If I'm wrong here I'd love to see the research as well.

    My homebrew conjecture says to add between 10-20 mins on to your late hops in your brewing software to get a guesstimate of how many IBUs they will add. I use 10 mins myself.
     
  4. Liam_snorkel

    كافر

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    Posted 12/10/12
  5. JDW81

    I make wort, the yeast make it beer.

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    Posted 12/10/12
    I can't help you with formulas or numbers, but have you tried a mini boil prior to pitching?

    I tried to find Argon's method, as he has an excellent description (with pics) on how he goes about it, but I didn't have all day to search.

    In a nutshell:

    Add your any bittering hops at 60 minutes and then any subsequent additions 10 minutes after you would normally add them (i.e. a 20 minute addition at 10 minutes). Once you get below about 20 minutes don't add any extra hops and cube as normal.

    Once cooled, draw off 10L of wort and bring to the boil and add your 10, 5 and flameout additions then chuck the pot in a sink full of ice water to chill.

    Strain into your fermenter with the wort from the cube, pitch your yeast, and hey presto; flavour and aroma from late hop additions.

    I've been doing this for a while now, and have been able to capture excellent flavour and aroma across a variety of styles. Yes, you don't get as much hop utilisation from late additions as you are boiling in a smaller volume of wort, but I see it is a small price to pay.

    My 2c.

    JD
     
  6. Damien13

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    Posted 12/10/12
    I agree JD, I do the same thing (but only use a couple of litres and don't strain) and I have noticed a massive jump in hop flavour and aroma.

    I have a sneaking suspicion my next purchase is going to be a Chillout however. Doing the extra step is little tiresome at times....
     
  7. Malted

    Humdinger

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    Posted 12/10/12
    I have started writing about this topic but have been too lazy to finish it. I have cut and pasted some of it and chucked some other things in.

    When we try to calculate how much isomerisation has occurred and contributed bitterness to our finished beer, this is where we use the term utilisation. It is what percentage of potential bittering compounds added to the wort (through the process of isomerisation) were actually turned into bittering compounds in the finished beer.

    Isomerisation is a process in which there is a structural change in a molecule without changing the overall composition of the molecule. There are a number of similar compounds of alpha-acids: humulone, co-humulone and ad-humulone are the most common and are the ones most of interest to brewing. These compounds do not contribute bitterness to the beer until they have undergone structural change.

    Utilisation is simply calculated as the amount of iso-alpha acid in the finished beer divided by the total alpha acids that were added to the beer multiplied by a factor of 100 to give a percent. In practice only 10-40% of the total alpha-acid added to the beer wort make it through to bittering iso-alpha-acids in the finished beer. For example, up to 38% of alpha acids bind to kettle trub.

    There are a whole wedge of factors at play. For instance, utilisation is influenced by temp, time, wort gravity, wort pH and a raft of other things.

    Palmer has a table that relates to utilisation over time vs wort gravity. http://www.howtobrew.com/section1/chapter5-5.html
    You can graph it like such:

    Utilisation_vs_time.jpg

    The important thing here is that gravity of the wort is important to determining hop utilisation and potential bitterness. Moving on, the above results are of wort at a constant of 100oC.

    I too have heard that 80oC is about the bottom limit for isomerisation of bittering compounds in wort. There does not appear to be a lower limit that I could find in literature. Moreover, it would appear to be that alpha acids are less soluble at lower temperatures* and isomerisation of alpha acids that are in solution slows down. I found discussion stating that isomerisation will occur at 50oC but it may take 204hrs for a significant proportion to isomerise.

    *Some folks I know made hop hash extract by seperating the lupulin etc in an ice bath.

    Hop literature suggests that hop acid isomerisation follows the Arrhenius equation. That is a formula for the temperature dependence of the reaction rate constant, and therefore, rate of a chemical reaction. For many common chemical reactions at room temperature, the reaction rate doubles for every 10 degree Celsius increase in temperature. Hop literature indicates that isomerisation halves for every 10oC below 100oC.

    How much extra bitterness might we expect from our 20 minute or 10 minute additions if they are left in the wort for an extra half or whole hour? I suppose it depends on what volume of hops you have added, their alpha acid%, cohumulone%, wort gravity, how quickly the wort cools and many other variables that can make trying to plot a curve quite irrelevant. One curve would not fit all.

    Flavour and aroma loss has a few factors too. Hops can contain hundreds of oil components and can contribute almost half of the aroma to beer. Temps lower than boiling may well volatise and drive off many of the hop oils, aromatics and flavour compounds. The majority of hop oils are easily oxidised and this leads to them loosing their ability to contribute aroma to beer. They are volatile in CO2 and can also be lost due to yeast scrubbing. There are lots of ways to lose flavour and aroma.
     
  8. losp

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    Posted 12/10/12
    Very interesting Malted.

    However, Given that we know all of the above factors that you mentioned.

    Following the Arrhenius equation, could some smart cookie not plot a line after making some assumptions such as the gravity is 1050, and it took 20 minutes to cool down to 80c. (i would be happy to do an experiment and take a temperature reading every minute until it gets down to 80c).

    Otherwise i guess i would have to line up 10-20 pots under a constant whirlpool and and put in the same weight and then tap samples out of them all by the time they are down to 80c and send it to someone with a spectro-whatchamacallit.... yeah.... no... :eek:
     
  9. Muggus

    Case swap whore

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    Posted 12/10/12
    This sounds interesting.
    I could imagine it would be a highly ineffective/inefficient means of bitter, but it would be interesting to see the difference in bitterness (harshness, etc), not to mention the amount of aromatic/flavour you get out of the hop.
     
  10. micblair

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    Posted 12/10/12
    Yep Hop isomerisation follows the Arrhenius equation for first order reaction kinetics:

    k = Ae^(-Ea/RT),

    where k= rate constant; A = pre-exponential factor; R = universal gas constant, T= temp (Kelvins) and Ea = activation energy (calc. 98.6 kjmol-1, J. Agric. Food Chem. 2005, 53, 4434-4439).


    All you need to know is that for every 10C change in temperature the rate of isomerisation doubles, i.e. at 120C you would get the equiv. hop utilization of a full 60 min boil in just 15 min; likewise at 80C you would require 4h to achieve what boiling would utilize in 60 mins.

    I'm not quite sure at what stage temperature then becomes a limiting factor for the solubility of humilinic acids, but I would certainly imagine it compounds with isomerisaton kinetics to result in even lower hop utilization. I have stopped worrying about all this and have purchased an immersion chiller. :beer:
     
  11. micblair

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    Posted 12/10/12
    Sorry, should have mentioned that Malowicki and Shellhammer (J. Agric. Food Chem., 2005, 53 (11), pp 4434–4439) study down to 90C.
     
  12. drsmurto

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    Posted 12/10/12
    Some of the papers i have read that may be of interest.

    A Kinetic Study on the Isomerization of Hop alpha-Acids. J. Agric. Food Chem. 2008, 56, 64086415.

    Factors affecting hop bitter acid isomerization kinetics in a model wort boiling system. J. Am. Soc. Brew. Chem. 2006, 64, 2932.

    Isomerization and degradation kinetics of hop (Humulus lupulus) acids in a model wort-boiling system. J. Agric. Food Chem. 2005, 53, 44344439.

    You could also try - Brewing Science and Practice (Briggs, D. E.; Boulton, C. A.; Brookes, P. A.; Stevens, R) but from my readings of it there is no discussion on kinetics, in fact the section on hops is quite sparse.

    The problems in trying to understand what on paper looks to be quite a simple chemical reaction are the large numbers of factors that impact on it - pH, wort matrix (which by itself is several theses), particulate formation. Add onto that the question no chillers want answered - how many extra IBUs do i get by not chilling which involves another plethora of variables in addition to those already mentioned, air temperature, air pressure, surface to volume ratio of the kettle, volume, density of kettle material, all of which change the rate of cooling which changes the rate of alpha acid isomerisation.

    Cheers
    DrSmurto

    p.s. no, I won't provide these papers in pdf format as that would break the licensing agreements between my organisation and the journals, which would result in me being unemployed (best case scenario). Google Scholar is your friend.

    p.p.s buy a chiller you lazy, tight arse bastards ;)
     
  13. losp

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    Posted 12/10/12
    So from all that then, i can assume that it is half as effective at 90c and 1/4 at 80 1/8 at 70 and then small/negligible after that.

    Or do i have it wrong?
     
  14. bignath

    "Grains don't grow up to be chips, son"

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    Posted 12/10/12
    Have been trying to get my head around this since malted posted this chart, but i can't find an answer.....sorry if i missed it..

    In the above chart, it appears to read that you get more utilisation at a lower gravity than a higher one, specifically 1030 compared to say 1040/50.
    However, i was always under the impression that 1040 was a kind of target that we were aiming for for utilisation of hops and also for the most appropriate conditions for building yeast starters etc...

    am i wrong in this? if not, how come the 1030 line shows a higher level of hop utilisation.

    Once again, sorry if this has been covered but i find the more technical side of stuff a bit daunting sometimes.

    .....i need a cigarette.
     
  15. micblair

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    Posted 12/10/12
    In essence. Bear in mind it's a reaction rate (time dependent), so a cube somewhere around 70-80C for a prolonged period (i.e >8h) will see significant hop utilisation from any late additions irrespective if they've been added directly to the kettle or the cube. I'm not going to discount mechanical forces such as boiling which will no doubt aid dissolution of hop components out of organic material, but until I know more about this, then I'm not going to comment further.

    So if you want to nail your calculated IBU (keeping all other things constant such as bitterness loss to trub, yeast, walls of the fermenter, kettle etc) the least you can do is chill the cube by submerging it in a bathtub till it cools to ambient, which will be better than doing nothing.
     
  16. micblair

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    Posted 12/10/12
    You should read this paper: http://journals.usamvcj.ro/agriculture/article/view/876/873
     
  17. losp

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    Posted 12/10/12

    I have just been running through the numbers (playing with half-life).
    If i put all of those numbers in a spreadsheet for example, and then take the mean temperature over the time taken from boil-out to 80C (anything less than that on a 0-30m boil is not likely to be more than a couple of IBU) it appears to be a reasonably close solution (or atleast nothing that i would be able to taste) for addition that occurs during that cool down period, and more so for anything that was added before.

    I think this information is useful to know, because assuming that this graph is correct i might be able to approximate how to get 7 minutes worth by putting it in at a certain temperature somewhere in the cool down process, and maximize my ROI B)

    [​IMG]
     
  18. felten

    Homebrew Conjecturist

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    Posted 12/10/12
    That graph is about as accurate as an airlock is for measuring fermentation.
     
    1 person likes this.
  19. Thirsty Boy

    ICB - tight shorts and poor attitude. Fuck yeah!

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    Posted 12/10/12
    theory shmeory.

    No chilled beers are measurably more bitter than beers which are not no-chilled. I know, I have in fact measured the difference. Enough measurements to be statistically significant for the fussy science types out there, iso octane extractions if you care.

    I made graphs and tables and all that shit.... dont ask, they are all gone in the great hard drive crash of years past. However, I have retained the useful result.... the useful result being that if you take a recipe and you look at your hop additions - the difference that will be made by no-chilling the beer is the same as you would get if you made your last hop addition and at the time you were meant to turn off your kettle... you forgot and left it run for an extra 10-15 minutes (ignoring volume changes) - then chilled it. Fast with an immersion chiller.

    That was all worked out using Pro-mash and the Rager ibu formula, which is what I use. Basically i just plugged in numbers till things worked out. So wort A ended up say 5% more bitter in the NC version vs the Chilled version, so i plug the recipe into pro-mash and click the boil time up till the IBUs have gone up by 5%. Repeat for all samples. Work out a range and call it as good a guess as any.

    Turns out its 10-15 mins. If you happen to shove an amount of hop pellets (loose) into your actual cube and not boil them at all, that'll add bitterness as though you had boiled them for 20-30mins.

    You want to "compensate" for no chill but use software that assumes you do chill? - calculate your bitterness as though you were going to make all your additions 10-15 minutes earlier in the boil (including your bittering charge) and then simply reduce the bittering charge till your expected IBUs match the recipe. DONT actually change when you add the hops. Not that hard really.

    And sweeties.... thats just about as close as you are ever going to get. I used to chill with an immersion chiller and swapped to a plate chiller... all my hops sat in a kettle full of very hot wort for 20-30 minutes longer than they used to. would that have changed my bitterness?? Of course it would. Does the brewing software take it into account? Hell no, but you dont see fucking thread after thread on AHB about how people cant calculate their bitterness properly anymore because they bought a plate chiller.

    How about the different IBU calculators that DO assume you chill? Try going into the settings of your software and changing from Rager to Tinseth, or Daniels, or "generic" and see what that does to the expected IBUs over a few different recipes. Or how about FWH?... my software defaults to FWH reducing IBU levels significantly vs a normal boil, other software defaults to it increasing IBU levels?? Oh - and how many of you take note of the date your hops were picked, then plug their proper age & the type of material they were stored in & the temperature they were stored at, into your software to estimate their degredation in IBU potential during storage. And what effect did the repackaging and storage conditions that happened at the HB shop before you even bought them have? Do you compensate for potential between hop flowers and hop pellets? - what about type 90 pellets vs Type 45 pellets and each of those vs flowers? What about different varieties of flowers whose cones have different physical structures which will affect the way that the hops resins are able to be physically dissolved in the boil? what about the vigor of your boil? What about the difference in utilisation potential between dark and light worts with different pH levels? hmmm? I could keep on going for a while too.....

    What I'm kind of unsubtly trying to get accross, is that ALL the hop formulas are just a moderately educated guess - and none of them are very accurate at all (able to measure remember). They ALL require you to stick with them and not change your technique, over a few brews and feedback the way the beer tastes into your recipe development. Adding a 10-15min "No-Chill Factor" into the mix is barely even going to make a ripple in the lake of mixed bullshit and guesswork that makes up Homebrew IBU calculations.

    Brew your beers the way the recipe says.... if you notice that your No-Chill beers (or all your beers if you only no-chill) are always a little more bitter than you'd like. Reduce the bitterness you add! Its that simple. If by chance you'd like a hint on how much to reduce it - well then, a good place to start is to calculate the bitterness in your no-chill beer, as though you'd boiled all your hops for 10-15min longer than you actually plan to. the increase in bitterness you get is how much you should reduce your bittering addition by.

    See how it works out - tweak as required to suit your brewery - sorted.

    TB
     
  20. Ross

    CraftBrewer AHB Sponsor

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    Posted 12/10/12
    Very wise words indeed, exactly what we do for our commercial beers & also our FWK production.

    Cheers Ross
     

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