During the wort boil, certain types of proteins can be coagulated. These proteins are primarily responsible for haze formation in the finished beer. However, the boiling temperature alone will not coagulate the proteins. Coagulation and precipitation require the action of the bubbles formed during a vigorous boil. Because these proteins are electrically charged molecules, providing a substance of the opposite
charge will enhance the coagulation. Irish Moss, carragheen, is a seaweed that when added when added at the rate of 1 teaspoon to a 5 gallon batch the last 15-20 minutes of a rolling boil helps attract coagulated proteins into clumps causing their precipitation during the cool down period.
The importance of a vigorous, rolling boil for protein coagulation cannot be emphasized enough.