IBU Calculations - How and Why?

I recently started to use your program more closely and i have a few questions concerning how you are calculating IBU's using the Tinseth method.

1.)First Wort Hop - your calculations actually raise the total IBU's but in ProMash the IBU's are lowered.  Why?

2.)According to www.realbeer.com/hops they use the OG (gravity factor) of the wort and a utilization table along with boil time (utilization factor) to calculate IBU's.  Does beersmith do this?

3.)Why do you use the pre-boil volume to calculate IBU's while ProMash uses the tinseth concentration factor which is preboil vol./postboil vol. (around 1.3)

4.)Beersmith is designed with pellet hops as its basis. Have you done an automatic hops utilization increase above and beyond the reported alpha acids reported for whole hops?  ProMash's basis is whole hops and they add 10% utilization for the pellet form.

5)Do you use the Hop Stability Index in any of your calculations?  It would be great if we could just enter the age of the hops right into the recipe to account for acid loss with time.

6.)How about adding the 5 major hop oil levels for each hop in the Hops Categories?  Could be helpful for designing beers.

The reason i started to look into this was b/c of a Sierra Nevada Clone from http://forum.northernbrewer.com/viewtopic.php?t=15532  
The hops and grain schedules were taken right from the head brewer's mouth, Steve.

According to Sierra Nevada's website the IPA is 37 IBU's and i don't know what calculation they used.

When i enter this recipe in ProMash like the author did it is 36.7 IBU's and it is 32.7 in Beersmith.  Everything is set to tinseth using their tinseth concentration factor of 1.3.  All other parameters are identical including volumes, OG FG efficency etc.  Why such a large discrepency even after the head brewer says it 37 IBU's and ProMash says its 37 too?  This is about a 10% difference.  If i change the Hops Utilization Factor in beersmith under my Equipment to 112.5% the IBU's are now 36.7.  Is this correct?  Thanks for a great program.  Much easier to use than others.

samsonite

Samsonite,
 Lots of questions - I will do my best!

1) The independent research I did on first wort hopping (process of adding hops during sparge and keeping it in boiler through the boil) indicates it increases utilization by approx 10% due to the extra soak time.  It would be counter-intuitive to have it reduce the utilization.  It is adjustable via the bitterness tab in the options dialog, however.

2) Yes, the OG and tables are all inside BeerSmith to calculate IBUs (depending on the method used).

3) I don't quite understand this question - the preboil volume drives the concentration factor and wort SG which factors into the calculation, but the final volume is certainly also used in the tinseth calculation.

4) I use pellet as the basis (most users use pellet) but if you change a hop type to Whole Leaf by editing it, BeerSmith will reduce utilization by 10% (default).  You can also customize this in the Options dialog, bitterness tab.

 5) The HSI is not used by default in a recipe, at the moment you need to use the hops age tool and enter the adjusted alpha instead.  Perhaps a future feature?

 6) I thought about adding these - the challenge is finding good data for every type of hop.  It was easy to find alpha and beta values, but many of the other parameters are hard to find and vary by grower and location.

 Last - I'm not sure what might account for the difference between the two programs.  Perhaps it is a difference in the way the original gravity is calculated based on the volumes used.  Tinseth specifies that the wort gravity is the gravity used during the boil.  However, depending on whether you use starting, ending or average boil volume your wort gravity and volumes can be different which will produce different utilization factors.  Also the other program adds in an additional 10% alpha for pellet hops which might be part of the difference.

 You can certainly up your utilization if you feel your numbers are consistently low.  Tinseth in general will produce lower utilization numbers than other IBU formulas.

Cheers!
Brad