Irish moss is a species of red algae that grows along the rocky parts of the Atlantic coast of Europe and North Ameria. It is a major source of carrageenan, used as a thickener and stabilizer in processed foods like ice cream and processed meats. It is also used in homebrewing as a clarifer. It acts as a coagulant to pull proteins and small particles out of solution to clarify the beer.
Usage: Add 1 teaspoon to the wort at the final 15 minutes of the boil. It works best when rehydrated.