How does Irish moss work?

Proteins are one of the primary constituents of hot break. Some of these proteins are known as haze active (HA) and negatively affect beer clarity (they make yer beer cloudy). The proteins are complex molecules folded up into three-dimensional structures that give them a positive charge.

Irish moss (Chondrus crispus) is negatively charged. When present in the boil it attracts the positively charged proteins like a magnet. While proteins would normally remain in suspension bonding to the irish moss forms a particle heavy enough to drop out.