Using a 12.5 aa hop with a 20 minute boil, this software shows 28.51 IBU which seems correct. When I change "boil" to "whirlpool" the utilization goes to 10% which seems ok. I then put 180 degrees for 20 minutes in and it shows the IBU to be 17.2. This seems excessive. If I change the utilization to 100% it goes to 170 IBU. Am I doing something wrong?

Whirlpool IBUs are pretty much from the twilight zone when it comes to the various calculators. It generally isn't the fault of the calculators, it's more that the various forumulae out there haven't kept up with how brewers add hops these days. Listening to some of the people who've created their formulae they're astounded how far they're applied from the original research (Tinseth's research was just whole cone hopping, none later than 15 minutes left in the boil). And the post boil additions are even more difficult with many more variables than just temperature and time affecting how we actually perceive those IBUs (and how relevant IBUs are once you move past the boil stage). From the analysis I've heard discussed the liklihood is that there's more IBUs than the standard 10% assumption gives, but most tasters don't perceive those IBUs as being as bitter as boil IBUs. So the 10% is probably an OK guess based on the knowledge people have at the moment. I tend to use it more as a point of reference, rather than some prediction of the number you'd see from the actual test. So if it was a mythical 17 IBUs last batch and I need more bitterness I adjust it up, knowing that the number may have been as high as 50 IBUs. Any reason in particular you're looking for a number that may match a lab based assay for that step?

I've found that if I use a 4% setting I get the results I want, based on the hops that I usually use, the temperature and length of whirlpool. I've adjusted my personal settings based on comparing commercial beers of known IBU rating to beer that I've brewed with very similar malt and hop profiles. I think most folks settle on a fairly low number. As far as the calculator goes, the only function that does anything to change the IBU contribution is the percentage of utilization. Neither the time or temperature change the IBU calculation, even though changing those in the brewing process will, of course, have a substantial impact. The only thing that the time and temp boxes are good for is documenting what you actually did during the brew. Bottom line...the calculator is useless in the predicting whirlpool IBU contribution and you have to do some trial and error, preferably in conjunction with consistent time and temp in the process, to come up with your own fudge factor.

The calculator gives you a starting point, an initial estimate. Once you brew a beer, adjust up or down to get the IBUs to where you need them. Come to think of it, all calculators are estimates. Use them to create your first try at a recipe, then adjust. Brewing ingredients are variable so you can't treat a calculator's results as gospel for any of the brewing variables.

Thanks for the input guys. I am trying to get to a particular number of IBU's and I know from Flameout additions that they add a ton of bitterness and this is first time doing an neipa where I'm whirlpooling at 180 which is much lower than a flameout addition so just trying to get a starting point. As mentioned above, I will just use this first batch as that starting point and go from there. Just don't want it to get to bitter as that's not what I'm going for.

I'd caution that IBUs are themselves at best a guess. They are a specific unit, mg iso-alpha acid per liter (ppm). Unless you have some very pricey equipment in your basement, you can't measure IBUs, only estimate. But as you mention, use the calculators to get to an approximation, then refine.

Sort of...At least with boil IBUs there are established mathematical formulae that the recipe editor uses. When you change the length of the boil time, the IBUs change in the recipe. When you change the whirlpool time or temperature (definitely both are strong factors in actual alpha acid uptake) the IBUs stay exactly the same. Only when you change the percentage is the IBU count changed. The 10 percent default is pretty much a WAG...that's not the case with the calculator for the boil function.

Well, it's not a complete WAG................... It's a studied WAG. Understanding the utilization of lower-than-boiling temperature hop additions is a brand new area of brewing, and at first experienced brewers and those who wrote brewing texts strongly stated that 0 isomerization happened at temperatures lower than at boiling. But we all know that isn't true. Trying to determine a formula that takes into account things like wort gravity, temperature, time, etc isn't that easy when there are that many variables, and some research still needs to be done to even come up with a formula for this. The best we could do was add the whirlpool/hopback hop additions to the software, give a default utilization percent that start with the boiling temperature, and allow the brewer to make the decision based on his results, his palate, and (hopefully) some lab testing on his own. I chill faster than some, but not as fast as others, so even if we had a perfect formula at the outset, the results would still vary greatly among brewers. By allowing each brewer to either go with the default or choose their own number based on their research and results, we can still have the whirlpool hops "count" toward the IBUs if desired. In my Beersmith 2 software, all late hops added at flameout or whirlpool always had a 0, and I knew that wasn't so for my big IPAs. This software allows me to make the decision on what to do with those numbers and I like that.

I understand that there's some research behind the effort to arrive at any figure to use as a default and that it's difficult to pin down a formula for the purposes of calculation where one doesn't exist. My point is that using 10 percent for every whirlpool scenario from 5 minutes at 180 an hour at 160 is arbitrary. I'm not suggesting that there's another or better way to include it in the calculator. I'm just saying that every brewer is on his/her own to figure out what their particular procedure is likely to yield and that's a fact that new brewers, especially, should be aware of.

I've come up with a way to use "aroma" rather than flameout so I can assign a percentage to the hops that I leave in from flame-out until late in the cool-down process.

That's what I was trying to say. The equations may be the most solid math since Newton invented Calculus but the inputs are variable and we can't reasonably QC them. I boil at 200 degrees, affecting my hop utilization.... You are right in saying that every brewer must figure out how to get the results they want on their own systems with their own procedures and the only way to do that is trial and error.

My wife used to work in a macro lager brewery doing QC (West End for the crow eaters out there). She still thinks the IBU assay was one of the least reliable of all the procedures she did. She's sure the machines are much better now, but it was a flaky number and would vary widely from the number on the packaging (or recipe, as it wouldn't be seen on a macro lager label).

I use the BrewersFriend calculator and found out that 4% utilization for the whirlpool is where I am at with my system. I did 3% for a long time, but got more bitterness and adjusted to 4%, which is more realistic for me. I haven't tested any of my beers for the actual IBUs, but have no reason to believe that something around 40 IBUs, could be 50, 60 or more. I find that a margin of + - 5 IBUs from the total calculated IBUs is OK. I do my whirlpools at 70C or 158F and I can tell you that if you are using a generous amount of hops, you will still get plenty of bitterness from it, even when the temperature is low. Anything upwards 5 oz will still add lots of bitterness.