Author Topic: Variations in IBU  (Read 5958 times)

Offline topremf

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Variations in IBU
« on: May 10, 2012, 01:00:19 PM »
I'm fairly new to this brewing business and a novice with BeerSmith, although have completed about ten batches and notice that the recipes from outside of BeerSmith (such as Brew Magazine) have significant IBU variations when added to BeerSmith, when all else is seemingly equal.  Is there something I'm not understanding?   This is also true of most SRM.

Offline MikeinRH

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Re: Variations in IBU
« Reply #1 on: May 10, 2012, 06:01:04 PM »
I totally agree with you. I was reading that there's actually a point where you simply can't add any more IBU's ... much like the point of absorbsion of sugar to iced tea. I'm experimenting with my last batch by just tossing hops into the boil vs muslin pouches or stainless steel balls (like tea strainers). I think Beersmith helps a great deal by illustrating what IBU's you "should" be getting. The reality, I think, is how the hop additions are conducted. Right now, I've got some nasty-looking stuff at the top and bottom of my fermenter. I'm looking forward to racking it off ... carefully! My plan is to condition in the fermenter for a total of three weeks, then stick the carboy in the fridge for a few days to see if I can get most of the "undesirables" to settle to the bottom.

Offline glienhard

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Re: Variations in IBU
« Reply #2 on: May 11, 2012, 12:04:44 AM »
Remember, all values are estimates from complex calculations.  BeerSmith takes into account everything from your brew equipment, to temperature, to the type of ingredient and everything in between.  For instance, IBU calculation can very depending on the efficiency/gravity, type of hop, AAU value and boil time based on your equipment profile, just for example.  I know brewers that have switched to always just adding the same amount of hops to the batch and not paying any attention to the AAU.

You also asked about the SRM, or color of the beer.  Again, this is an estimate based on calculations.  If you are going by the picture on the screen, this will almost never be accurate.  I say that because, unless you spend thousands of dollars on a monitor that is calibrated to true color and it is kept calibrated, colors on the screen are never true to what you would see in real life.  It is more just a point of reference.

I hope all this helps.

Cheers!

Offline MaltLicker

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Re: Variations in IBU
« Reply #3 on: May 11, 2012, 01:06:36 PM »
....... notice that the recipes from outside of BeerSmith (such as Brew Magazine) have significant IBU variations when added to BeerSmith, when all else is seemingly equal. 


Two things going on here.  The various hops models (Tinseth, Rager, etc.) use different assumptions about utilization/extraction of alpha acids.  Many magazines use Rager, as does Jamil in his oft-quoted book.  To precisely recreate the recipe in BeerSmith, you need to know what model they are quoting. 

BeerSmith uses Tinseth by default, so if you're trying match a recipe, try toggling the method under Options \ Bitterness. 

One of my favorite features in BS2.0 is being able to show both Tinseth and Rager onscreen at once.  This reveals that there is not just one IBU number (as fact) but actually multiple estimates of the likely IBUs.   I have an IPA I'll brew soon with 9.1 IBU difference between Rager and Tinseth.  The Rager at 69 is just under the style limit of 70 while the Tinseth is comfortably under at 60. 

Offline topremf

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Re: Variations in IBU
« Reply #4 on: May 15, 2012, 11:55:25 AM »
Thanks folks for your sage advise/comments.  Interesting about the difference between Tinseth vs. Rager.  Did not know that.  Guess a closer look at the various BeerSmith functions is certainly warranted.  Regarding IBU variations based on equipment boil size and SG.  Not sure I understand why the difference if the end batch size is the same amount and SG.  Must be something going on there.  Will research that as well.  I do a lot of partials and so use an abbreviated boil, topping up before tossing the yeast and do notice some significant IBU differences with that method vs. all grain.  I'm still struggling learning to correctly use the boil equipment function and oft times get it wrong.

Offline jomebrew

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Re: Variations in IBU
« Reply #5 on: May 16, 2012, 09:29:51 AM »
The higher the calculated IBU, the more the IBU will be off.  Measurements using a Spectrophotometer always show much lower IBU values than those calculated. 

Once you plug in the hops and alpha acids into beersmith, you simply ignore any suggested  IBU from the source.  As mentioned, Beersmith takes more elements of the system into consideration to give you a guideline.

As you are experiencing, your own process also affects the perceived bitterness in the beer.  This is where you focus doing the same thing over and over and adjust your hop additions to match your process.  Being fairly new to brewing, you should focus on a few of the basics.  Clean and Sanitize everything, twice.  Get a process down that you are comfortable with and stick to it for a while.  Finally, control your fermentation temperature.  The first and last will get you good beer.  The middle helps get good beer each time.   When you got those down, start tweaking recipes or build your own.

Happy Brewing

Offline MaltLicker

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Re: Variations in IBU
« Reply #6 on: May 18, 2012, 08:05:25 AM »
...........Regarding IBU variations based on equipment boil size and SG.  Not sure I understand why the difference if the end batch size is the same amount and SG. 

Tinseth in particular focuses on two factors:  boil time.....longer boils isomerize more bitterness from the AA% there; and wort gravity........higher gravity has a negative impact on that ismomerization.  So those factors off-set each other somewhat.  Long boils of a low SG wort will isomerize lots of AA% from the hops, and 60-min boils of a 1.090 wort (esp. a partial boil) will isomerize less.   Any model is just an estimate of what to expect for bitterness, and neither will be exactly right very often. 

One tip for partial boils of extract batches is to add a portion of the DME late in boil, so AA% from hops has better chance to isomerize in lower gravity wort over the full 60 mins boil. 


Offline topremf

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Re: Variations in IBU
« Reply #7 on: May 19, 2012, 07:25:08 AM »
Hey MaltLicker,  I have noticed that most recipes specify that the DME is added at the beginning of the boil and that LME can be at the beginning, end, or in batches.  Why is DME then seemingly always up front?  I have never seen a recipe calling for it to be added in the middle or the end.

Offline MaltLicker

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Re: Variations in IBU
« Reply #8 on: May 20, 2012, 12:33:53 PM »
Maybe b/c the powdered form mixes less well?  Dunno.  But I know many people do it. 

With any extract, turn off the gas when adding extract to avoid scorching it as it falls to bottom unmixed. 

 

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