Calculating IBU's. Is Brewing software accurate enough, or is my recipe off?

I'm just wondering do most people here use software to calculate their beers specs? I was using tastybrew.com which I've used before to check individual specs such as IBU's and priming sugar volumes. I decided to check the IBU's on an Avery New World Porter Clone I am doing. The recipe states it's 44 IBU's, however, this calculated just around 17. How accurate are these things? It could well be my recipe? I got it from BYO so it should be decent.

I tried to copy and paste the specs, but it was all over the place, the schedule is basically:

0.33oz Coumbus@60
0.25oz Columbus @30
0.96oz Columbus @0
1.960z Fuggles@0

In order to correctly estimate the IBUs, you also need to know the boil size and the ingredients of the brew.

You also need the percentages for the alpha acid units to calculate them correctly and the percent changes year to year so that could be throwing off the math as well.

Which issue of BYO is it in? I can take a look at the recipe, and see why it's so different for you.

Thanks Yooper, it's BYO's 150 classic clones. I had entered all percentages and boil volumes, I tried to copy and paste the results here but it was messed up

Ok, I found it. What size boil are you doing?
Extract or AG?

Also (most important, actually!) take a look at the hops schedule in the book. Thay have .33 of 13% AAU Columbus. If you're entering Columbus at 10% AAU, the figure will drastically change. So, check your hops, and check the calculator to make sure you're comparing apples to apples.

I'm doing the partial mash extract version. I'm boiling 23 liters (6 gallons)

My columbus are actually 14.2%. The fuggles are slightly less in AA% but they are being added at whirlpool and won't contribute much to the IBU's

You're right- that recipe has you do a late extract addition, which increases hops utilization but it's no where near 44 IBUs. I come up with 16.7 if you follow their recipe, with the 2.5 gallon boil and late extract addition. With a full boil, I come up with 20 IBUs.

I never had that beer, but would think that the recipe is jacked up. I have the issue, but I've never brewed anything from it so I don't know if it's just this one recipe, or many of them.

Thanks Yooper, thought so, It's not a huge deal I guess, I can just adjust the bittering hops slightly to get to 44 or so IBU's

Graeme said:

Thanks Yooper, thought so, It's not a huge deal I guess, I can just adjust the bittering hops slightly to get to 44 or so IBU's

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I've never had that beer- but 20 IBUs isn't out of line for many porters. I guess that is what you have to decide- is it a 44 IBU porter? Or is it a 20 IBU porter? I can't help you with that, since I don't know the beer. Can you go to Avery's website or google it, and see what others think of the bitterness level?

yeah I just had a look on their site, it comes up as 45 IBU's.

Graeme said:

yeah I just had a look on their site, it comes up as 45 IBU's.

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You can increase the bittering hops (only) to get you to the 45 IBUs, then, if you want to get it closer to the original IBUs.

Yeah, the last porter I did was around 40 IBU's and it was pretty spot on. I know around the 20 IBU mark isn't unheard of for a porter but I reckon this would benefit from a little higher. Thanks for your input on this Yooper, you've been a great help on more than one occassion