Is the Rager IBU formula real-world-accurate?

Rager seems to give me seriously inflated numbers but I thought I'd try it because it is the formula used throughout a Jamil Zainasheff recipe book I picked up recently.

I'm working through my recipes now and am trying out the different formulas to see which IBU formulas fit my "real world" experience.

Plugging in Rager gives some of my brewed recipes IBUs up in the IPA-range...even for brews that aren't particularly hoppy.

As an example, my current recipe for a winter warmer is 64 IBUs via Rager and 26 IBUs via Tinseth! I'm shooting for around 50. Should I just take the average of the two and call it good? LOL!

What formulas are you guys using? What jibes best with your taste experience?

I use Tinseth because I have always used Tinseth.

there is a nice archive Basic Brewing podcast where they compare all the available curves to actual tested samples and very few were close, IIRC.

GilaMinumBeer said:

There is a nice archive Basic Brewing podcast where they compare all the available curves to actual tested samples and very few were close, IIRC.

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That's disheartening.

Have you got a link to the podcast or remember which, if any, equation was "close enough for jazz"?

Basic Brewing™ : Home Brewing Beer Podcast and DVD - Basic Brewing Radio™ 2007

July 5, 2007 - Measuring and Predicting IBUs

It's been a long time since I listened but I think the results showed Tinseth was closer than any, consistently.

My apologies if my memory is .

Thanks! I'll check that out tonight when I get home.

I use Tinseth, to my taste it undershoots by a few IBUs, but on the whole, it is what i'm used to and what I work with.

They are all very rough guesses. I use Rager, but only because that's what I used when I started.

As an example...If I'm trying to design an APA with around 30 IBUs for a medium OG (45), based on my experience I figure maybe I'll need somewhere around an ounce and a half of 5.5AA Cascade at 60 mins then maybe another ounce at 15 mins.
I just plugged that into my software:

Tinseth - 28.2

Rager - 38.5

That's a 10 IBU difference and, even though Tinseth doesen't look quite right, to my mind Rager seems way out of whack.
I'm thinking I'll start checking commercial clone recipes with software against the commercial brewer's published numbers to get a feel for how far off the different calculation methods are...

Since I've recently started formulating my own recipes after years of brewing set recipes, brewing has gotten much more...um..."interesting". LOL!

None of the formulas are right if you expect exact numbers. There are many factors involved that are outside the simple here is the boil time here are the hops. For example, the yeast pitching rate affects the final IBUs of the beer, but none of the formulas take that into account.

Why use a formula at all then? Well, at least it gives you a benchmark you can use in your own brewing. That is why it is important to always use the same formula for all of your brewing. When you brew something that was 50 IBU by formula, remember what it tastes like. Next time you want something with that level of bittering use a setting of 50. It really doesn't matter if the real world IBUs were 10 or 100. You're just trying to have something as a a bench mark for your own brewing.

Pick a formula, stick with it, and learn how the results match your expectations.

Some software will uses an average. That's what I do.

yeah. What JZ said....

jamilz said:

None of the formulas are right if you expect exact numbers. There are many factors involved that are outside the simple here is the boil time here are the hops. For example, the yeast pitching rate affects the final IBUs of the beer, but none of the formulas take that into account.

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Understood. I'm not expecting exact numbers but wanted to get a feel for which formula came closest to real-world numbers. I listened to the aforementioned basic brewing episode and Rager did better than the other formulas most of the time but when it was off, it was way off.

jamilz said:

Why use a formula at all then? Well, at least it gives you a benchmark you can use in your own brewing. That is why it is important to always use the same formula for all of your brewing. When you brew something that was 50 IBU by formula, remember what it tastes like. Next time you want something with that level of bittering use a setting of 50. It really doesn't matter if the real world IBUs were 10 or 100. You're just trying to have something as a a bench mark for your own brewing.

Pick a formula, stick with it, and learn how the results match your expectations.

Click to expand...

Thanks! My main issue was trying to nail down which formula to stick with.

I have been using Tinseth regularly, but I think its numbers are a trifle low and I may switch to Rager.

BTW - The thing that made me start this thread, your book on brewing to style is excellent and I've learned a lot, not to mention made some great brews along the way. Thanks!

bakins said:

Some software will use an average. That's what I do.

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Not a bad idea. It kind of harks back to the joke I made in the initial post in this thread.

They're all screwy at one point or another. I think lots of people prefer Tinseth and lots of people started with Rager. Either is really fine and if you have any reason to pick one over the other, then it is a good reason.

More and more I'm finding Rager seems to reflect later boil additions more accurately.

I've had a couple of Pale Ales I designed using Tinseth come out way too hoppy recently.
(...still drinkable but definately not what the doctor ordered )

I've pretty much decided to switch to Rager when formulating my recipes from now on.

do pro brewers favor one formula over the other? say if i read the IBUs posted by Rogue on a particular beer, how do i know if they used rager or tinseth?

Pro brewers will often not estimate IBUs but actually measure the IBUs in the final product via chemical analysis.

Unfortunately that's just not economically feasible for home brewers.