Tinseth modification for pellets compared to whole hops?

[man_beach]

I've been happily using Glenn Tinseth's formula to estimate IBU (using leaf hops) for the past 16 years. But now some of the hops which I use are only easily available in pellet form. I've read online that you should use anything from 10% to 20% less pellets that whole hops for the same IBU. So, if you also use Tinseth's formula, how much do you adjust it for pellets vs whole please?

I'm assuming that if (for example) you need to use 10% less pellets, a simple modification of the alpha acid value would work. So treat 6% alpha acid pellets as if they were 6.6% in the formula?

Thanks.

[RobP]

Do you use any brewing software? If you do, the software does it for you. You just input whether you use hop cones or pellets.
Anyway, the difference is in the order of 5%, which probably wouldn't be detectable in the real world.

[man_beach]

I devised my own software spreadsheet when I started all grain brewing back in the 1990's. It's worked fine for me so far - until hop pellets became more common. The hopping is calculated using Glenn Tinseth's formulas. The malt is based on Graham Wheeler. Additional information from Zymurgy magazines.

Surely I can't be the only person out there who uses their own formulae for working out their recipe?

[MTW]

Is it not a utilisation factor? This article says perhaps 25% for leaves and 35% pellets. Also factoring in the hop storage index, with pellets retaining AA better, due to reduced oxygen exposure (less surface area).

http://www.uvm.edu/extension/cropsoil/w ... -Panel.pdf

[man_beach]

Thanks, MTW. The article gets a bit heavy as you go on, but the basic information there is something that I can work with and adapt Glenn's formula to suit.

(For information, here is a link to Glenn's original article if anyone wants to devise their own spreadsheet for calculating IBU rather than use someone else's software (such things weren't available when I started brewing!) - http://realbeer.com/hops/research.html)