Cooling the Wort

Now, your wort is boiling hot. But the yeast needs a temperature of about 70 degrees to survive. It's important to cool the wort quickly so that no other organisms can thrive in the wort and compete with the yeast or create off flavors. No harmful bacteria has proven capable of surviving in beer (that's why it was invented in the first place), but unwanted organisms can ruin a batch.

Remove the socks full of hops and add the 2-3 gal of chilled water. That should bring the wort down to about 100 degrees. If you have a small brewpot, you can empty it into the carboy before adding more water, but insert your thermometer or some other metal object into the carboy first, so that it touches the side. This will prevent cracking.

Cool your wort the rest of the way using whatever methods are availible to you. The most common is giving your carboy an ice bath.For some pointers on how to do this, check out this video: