I would really like to read about these experiments, do you have a link?
"The tricky part is determining what your hop utilization is. Factors that effect hop utilization
are length of the boil, wort gravity, vigor of the boil, wort pH, age/condition of hops, hop form,
hopping rate, boiling temperature, shape of kettle, filtration losses, etc. Shorter boiling times, higher
wort gravity, increasing the hopping rate, fermenting with a more flocculent yeast and using hop bags
will generally lower hop utilization. Using pellets instead of whole flowers, using fresher hops, and
increasing wort pH will increase utilization. In general, the utilization achieved will be in the range of
20-35% under ideal conditions, with a vigorous 1 ½ hour boil and the hops boiling freely in the wort.
Extractions for homebrewers are generally estimated at 20%. The only way to calculate the actual
IBUs in a finished beer is through lab testing."
Can be found here:
www.mgriesmeyer.com/doatest/bjcp/hop%20topics.pdf
"There are many other factors that affect the iso-alpha-acid utilization in beer, but most of them are very hard to quantify. The only method that even attempts to quantify any other effects is the Garetz method. Garetz recommends
Fhb= 1.0 for hops loose in the boil,
Fhb= 0.9 for hops in a hop bag, and
Fhb= 0.8 for hops in a hop bag stuffed full.
A yeast flocculation rate factor(Fyf ) of 0.95 is recommended for slow flocculation, 1.0 for average flocculation and 1.05 for fast flocculation. The filtration factor (Ffil) varies from 1.0 for no filtration to0.975 for aggressive filtration.
Found here:
http://www.scribd.com/doc/47604590/zymurgy-IBUs
Garetz refers to Mark Garetz who wrote
Using Hops: The Complete Guide to Hops for the Craft Brewer
I can't find anything quantitative online at the moment but if you look into Garetz's research you will see that utilization inside a hop bag is 80-90%. I think the most important thing when using a bag is to make sure it is submerged and make sure that it isn't very full. The hops need to come in full contact with the wort to increase utilization. Obviously, this is much easier without a bag.
