Irish Moss
Almost every decent recipe includes Irish moss so if you haven't used it before, you're missing out. This wonderful clarifying agent is neither Irish nor moss - it's actually an algae called Chondrus crispus.
Although this ingredient is in nearly every recipe people still tend to misuse it, so my goal is to help you understand what it does a bit better so that you can reap the most benefits from this wonderful red algae.
Irish moss grows all around the Atlantic coasts of North America and Europe, in fact, if you've ever swam in the north Atlantic you've probably been tangled in your fair share of it! There is so much of this wonderful algae that it is the main (only?) industrial source of carrageen that's used as a thickener in many foods like ice cream and lunch meat.
As a brewer you will use it not to thicken your beer but instead to clarify it. The process works in a similar way to a rain cloud. A cloud is formed of water vapor that has condensed enough to be visible. This condensation happens on something called a condensation nuclei; small particles that attract water vapor. Eventually these nuclei catch enough water to become droplets and then we get rain! Irish moss works in a similar way by being the condensation nuclei for proteins and other trub solids that float throughout your wort.
The way you can most benefit from the moss is simple; toss in 1 tsp, 15 minutes before your boil is done. After your beer has cooled to about 75F; stir it, creating a whirlpool and encouraging the particulate to migrate to the center, cover it and let it sit for an hour or so. By doing this you're giving the particulates more than enough time to settle to the bottom and thus clarifying your beer before you even ferment it! To make sure to keep those particles out of your fermenter, simply siphon off the top and leave as much of the particulate behind. You will find that clear wort will run through your siphon and although the yeast will need it's turn to settle later on, this step will ensure that the protein by-products of the boil will not make it into your fermenter or your final beer.