hop utilisation - late hopping.

[steve_flack]

Not until next week at least as I've got the rest of the week off.

[oblivious]

I will try and throw it up in the morning

[Gurgeh]

I keep forgetting some of the great stuff we have in the archives

do we!
it's an amazing achievement that this forum caters for idle chat & banter, newbie stuff or intermediate stuff, and yet when serious questions are asked, they are taken seriously and serious answers, solutions, and workarounds are presented.

[Graham]

I'm in my hop phase at the moment.

I'd never have guessed

Well every true artist works in phases, even P-artists. At least I cannot be accused of not thinking things out. It doesn't stop me getting things wrong, but at least I have though the subject out thoroughly before getting it wrong.

It's all looking very interesting. Very much looking forward to see it working

Well, it gets a little further advanced as time goes by in dribs and drabs. At the moment it is focused on doing the recipes for BYO, which it does. When that (ruddy) book is out of the way, I'll add the things that make it usable, like ingredient editors and a method of saving and retrieving recipes, which are the major things that it lacks at the moment.

Don't expect too much of it though. It will just calculate recipes, but well, I hope, and in a more brito-centric manner than current offerings. It will not do inventory stuff, or anything like that; If someone is too lazy to get up and look in the freezer to see what hops he has in stock, then tough - go out and PAY for something that saves the walk.

It will not suit Americans in its current form because it is all metric, DKL, and EBC, but that might change at some point.

[Graham]

If someone is too lazy to get up and look in the freezer to see what hops he has in stock, then tough - go out and PAY for something that saves the walk.

I can cut and paste or 'print screen', paste a print so I don't need a recipe archive either

You do seem keen. You are the one of the very few that has shown any interest in it so far. Perhaps I'll have to arrange a pre-beta version for you, when my broadband is on a surer footing. I expect it to go off any time now.

You actually don't need to cut and paste. It will save in .rtf and HTML as it stands. What you can't do is import it back in again if you want to modify the recipe further. The rtf format probably will not be in the final version; that is only there so that I can import recipes straight into my word processor for the book, it is not "complete" rtf, just the bits I need, and probably does not meet any standards - it'll probably go and I'll just keep HTML, plus some basic save and retrieve format. HTML is good enough if people want to save a recipe in some hard-copy or printable form.

[oblivious]

Isomerization and Degradation Kinetics of Hop (Humulus lupulus) Acids in a Model Wort-Boiling System

In conclusion, the experimental data were consistent with a reaction order of one, for the isomerization of alpha acids to iso-alpha acids. This agrees with previously published work, which examined isomerization kinetics in both model systems and actual wort boiling (3, 4, 8 ). The reaction rate k1 is a function of temperature (eq 9), with corresponding activation energy of 98.6 kJ per mole.

Extended boiling times (beyond two half-lives of alpha acid concentration) showed significant degradation of iso-alpha acids to uncharacterized degradation products. Although degradation products could not be directly quantified, their concentrations were inferred from the difference between starting alpha acid concentration, and the sum of alpha acid and iso-alpha acids present at each data point. Assuming the degradation reaction had an order of one, rate constants were also determined for the conversion of iso-alpha acids to the degradation products. The reaction rate k2 is a function of temperature (eq 10), with a corresponding activation energy of 108.0 kJ per mole. The two rate constants can be used to calculate the concentration of iso-alpha acids at any given time, accounting for both the amount of iso-alpha acids produced by isomerization and the amount of iso-alpha acids lost to degradation, as described above.

The results obtained indicate that the rate of isomerization roughly doubled for every 10 C increase in temperature (average change was 229% per 10 C increase). Isomerization of cohumulone to isocohumulone proceeded at a rate equivalent to that of humulone and adhumulone. High temperatures quickly led to degradation products, as evidenced in the dramatic decrease of iso-alpha acid concentration beyond 18 min of heating at 130 C. While the rate of isomerization slowed at temperatures below 100 C, substantial amounts of iso-alpha acids were still produced at 90 C. This is significant if hot wort is held at temperatures just below boiling after the kettle boil is completed, while in the whirlpool, or awaiting transfer to a heat exchanger.

Beer presents the brewing researcher with a complex matrix of chemical compounds, and study of a model system is often necessary to secure reliable data pertaining to a single particular area of research. While the application of the results achieved herein may be restricted, such study is undoubtedly necessary to break down the complex process of utilization into its subcomponent parts and begin a complete understanding of the entire process. The model employed in this research allowed calculation of the net amount of iso-alpha acids produced during heating under specific conditions and defined how the kinetics varied with altered conditions. While isomerization kinetics can thus be defined, the model is yet incomplete in terms of utilization. Knowledge of the rate of loss to trub formation (and other interfering factors) would be required to fully define the concentrations of iso-alpha acids in a real-world wort-boiling system. Nonetheless, this new knowledge of the kinetics of isomerization allows estimations to be made regarding how bitter acid concentrations would be affected by altered boiling conditions.

Equation 9, 10

[maxashton]

He can do science, he can.

[Aleman]

I think the most pertinant part of that article is

The model employed in this research allowed calculation of the net amount of iso-alpha acids produced during heating under specific conditions and defined how the kinetics varied with altered conditions. While isomerization kinetics can thus be defined, the model is yet incomplete in terms of utilization. Knowledge of the rate of loss to trub formation (and other interfering factors) would be required to fully define the concentrations of iso-alpha acids in a real-world wort-boiling system.

so while the amount of isomerisation changes the iso alpha acids may not be utilised (Loss to trub ect) which a lot of the mathematical models take into account . . . which is where I think the Gravity factor comes from, higher gravity beers have higher amounts of protein and subsequently more iso alpha acids lost to trub. Just a thought

[oblivious]

Protein denaturation is a very ramdom event, probably more so when combined with hop acids. It would not surprise me if this was also suited of chaos modeling

[Graham]

so while the amount of isomerisation changes the iso alpha acids may not be utilised (Loss to trub ect) which a lot of the mathematical models take into account . . . which is where I think the Gravity factor comes from, higher gravity beers have higher amounts of protein and subsequently more iso alpha acids lost to trub. Just a thought

'Tis true that the gravity factor should really be trub factor, and based on the nitrogen in the grist. Obviously a grist that has a lot of crystal malt or sugar will have less nitrogen / protein than an all pale malt grist, less trub and thus better utilisation. It is true that gravity is probably a good enough approximation; crystal malt, sugars and adjuncts are only used in small quantities in quality beers, but gravity isn't the true story.

My major objection Tinseth's work, among others, is that his gravity factor follows an exponential law, which clearly it cannot be. It has to be substantially linear - twice as much trub, twice as much bitterness lost - linear.

I have done some sums comparing a linear model to Tinseth and, quite frankly, there is not enough difference to worry about, roughly +/-10% difference worst-case between 1030 and 1100, and with a 30 IBU beer that is an error of 3 EBU, well below taste threshold.

However, the fact remains that Tinseth's assumption as to why this happens is wrong and the shape of his curve is also wrong, even if it doesn't make much difference.