How would you calculate IBUs for a continuously hopped beer

[malc]

IBU's for a continuously hopped beer like DFH 60 min? We are doing an IPA and were thinking of trying to do something like that.

 

[Cliff897]

I have no idea. I suppose that you'd need to be tracking the extraction rates and the time in the boil. I'm guessing that it would probably require some pretty sophisticated equipment along the lines of a mass spectrometer. This because you really can't quantify with any precision how a particular hop will infuse the wort and boil temperature changes with altitude. So I'd guess you'd have to have sample the wort itself.

However, the process of adding hops at different times during the boil is one I use most.
I usually end up with a couple gallons worth of spent hops.
It's well worth the effort.

 

[Beernik]

You'll want to find the Tinseth equations. If you know calculus, integrate with respect to time.

Otherwise, and this is what I'd do because it would be much easier, set up a spreadsheet and step through it. Figure out what fraction of an ounce you add each minute and calculate that IBU addition. Then add them all up.

 

[malc]

That's what i figured beernik. Been a while since calculus, so I think if I bother I will go with the second method. Thanks guys.

 

[Beernik]

Now that I have my computer I can post the reference.

http://www.realbeer.com/hops/FAQ.html

To calculate IBUs, the formula is simple:

IBUs = decimal alpha acid utilization * mg/l of added alpha acids
For those who want to make adjustments based on their own brewery, he offers the following:

Metric Units

mg/l of added alpha acids = (decimal AA rating * grams hops * 1000) / (liters of wort)

Non-Metric Units

mg/l of added alpha acids = (decimal AA rating * ozs hops * 7490) / (gallons of wort)

The decimal alpha acid utilization is calculated using Tinseth's two empirical factors: the Bigness factor and the Boil Time factor.

Decimal Alpha Acid Utilization = Bigness Factor * Boil Time Factor


The Bigness Factor accounts for reduced utilization due to higher wort gravities.

Bigness factor = 1.65 * 0.000125^(wort gravity - 1)

The Boil Time Factor gives the varying utilization based on boil time:

Boil Time factor = (1 - e^(-0.04 * time in mins)) / (4.15)

Some comments from Tinseth:

"The numbers 1.65 and 0.000125 are empirically derived to fit my data. The number 0.04 controls the shape of the util vs. time curve. The factor 4.15 controls the max util value--make it smaller if your util is higher than mine.

I'd suggest fiddling with 4.15 if necessary to match your system, only play with the other three if you like to muck around. I make no guarantees if you do.

You might notice that the shape of the util curves is very similar to that of Randy Mosher's. He and I seem to have independently arrived at the same conclusion.

The really cool thing about these new equations is that they are easily customizable. I believe the basic form is correct--by playing with the different factors, different brewers should be able to make them fit their breweries perfectly. The root of the equations is the basic first order chemical reaction, i.e. the AA isomerization seems be first order (or pseudo-first order)."

 

[maskednegator]

The integral of (decimal AA rating * (ozs hops*t)/(boil length) * 7490) / (gallons of wort)*(1 - e^(-0.04 * t)) / (4.15) with respect to time is a huge pain in the ass. Excel can give you an iterative solution much more easily.

 

[Beernik]

I think you did something wrong. I think the only t is in the e^t.

Everything that isn't t can be pulled out of the integral, which should something of the form:

A * integral of [dt] + B * integral of [e^(-0.04t)*dt]

evaluated from t = 0 to t = 90.

that should be easy to find in a table of integrals.

But unless someone has a way to actually hop at an equal rate continuously, I think stepwise in excel is more accurate to what's being done by the brewer.

 

[maskednegator]

I think you did something wrong. I think the only t is in the e^t.

Everything that isn't t can be pulled out of the integral, which should something of the form:

A * integral of [dt] + B * integral of [e^(-0.04t)*dt]

evaluated from t = 0 to t = 90.

that should be easy to find in a table of integrals.

But unless someone has a way to actually hop at an equal rate continuously, I think stepwise in excel is more accurate to what's being done by the brewer.

The other t is for hop quantity as a function of t. total hops/boil time * t = hops in solution at time = t. It's still easier than I made it out. You get something that looks like t-t*e^ct. not too hard.

 

[Cliff897]

You'll want to find the Tinseth equations. If you know calculus, integrate with respect to time.
[...]set up a spreadsheet and step through it. Figure out what fraction of an ounce you add each minute and calculate that IBU addition. Then add them all up.

That would take all the pleasure out of brewing for me.
But, I don't have a head for numbers.

 

[aliu630]

NERDS!!! jk

 

[Beernik]

LMAO!

This post is at least ten characters.

 

[malc]

I found this site while searching for a calculator. Maybe some of you have seen it before. If you scroll down there is a calculator that uses the Tinseth equation Beernik mentioned. I just plugged my values in and added up the results. Nice and quick. Although, the teacher in me was yelling at myself to show my own work.
http://www.rooftopbrew.net/ibu.php

 

[BendBrewer]

BeerSmith offers a free trial. Does all the work for you.

 

[malc]

BeerSmith offers a free trial. Does all the work for you.

I do have beersmith, but couldn't find exactly what I was looking for without doing an awful lot of typing. I guess I was looking for the lazy way out.

 

[GilaMinumBeer]

Subjectively.........

 

[BendBrewer]

I do have beersmith, but couldn't find exactly what I was looking for without doing an awful lot of typing. I guess I was looking for the lazy way out.

Start with one of the supplied recipes and start changing things.

Volume of boil water affects hop utilization and this is reflected in the Expected IBU number.

So will changing hops, AA% and boil times of each of the hop additions.

I try to stick within the beer guidlines, and tweek the amounts accordingly to reach the correct Expected IBUs and gravities. A lot of it is just point and click.

 

[moose123]

Wow

 

[el_caro]

I found this one - maybe it is worth a try
&#8730;( -e^( &#960; i )) + sin^2(e) + cos^2(e) + sup{ x in R : x^3<343 }

I am going for a beer let me know if it works.