First Wort Hopping
First wort hopping is an old, yet recently rediscovered process consisting of adding a large portion of the finishing hops to the boil kettle as the wort is received from the lauter tun. As the boil kettle fills with wort, the hops steep in the hot wort releasing their volatile oils and resins. The aromatic oils are normally insoluble and tend to volatlize during the boil. By letting the hops steep in the wort prior to boiling, the oils have more time to oxidize to more soluble compounds and a greater percentage is retained during the boil.
Only low alpha acid finishing hops should be used for First Wort Hopping with the amount being less than 30% of the total amount of hops used in the boil. Therefore, hops used for First Wort Hopping should be taken from hops intended for the finishing addition. Although the hops are in the wort during the long boil, the bitterness is increased only slightly. First Wort Hopping results in a more refined hop aroma, a more uniform bitterness (i.e. no harsh tones), and a more harmonious beer overall.
First wort hopping is a mystery. An interesting recent study by Preis and Mitter (Brauwelt Int. 13:308-315, 1995) found that first wort hopping significantly increased IBU's and lowered the content of known hop aroma compounds. Taste panels showed preference for first wort hopped beers and indicated a cleaner, finer bitterness and a fine, more rounded hop aroma. Two caveats here are that they were looking at German pilsner beer where all the hoppings were with noble hops, and they moved more of their total hop charge to the first hopping. This strategy may not work well for beers where different kettle hoppings are with different hop varieties. Late hoppings are often important for an intense hoppiness that the Germans are not looking for. It was suggested by Bill Pengelly (New Brewer, 19(5), 19-22, 1995) that this phenomenon may be due to the antioxidant properties of hop polyphenols. Normally during sparging and kettle fill there is significant aeration and heat to promote wort oxidation, and hop polyphenols from first-wort hops may help in this regard. However, this is speculation at present.
You will lose a lot of IBUs in the foam you skim. If you whirlpool and use a kettle coagulant (i.e. Irish Moss), protein denaturating in the foam should not be a problem. However, predicting hop utilization with first wort hopping and skimming is difficult and some experimentation is necessary.