Cooling the wort
Once the boil is finished, it is important to drop the temperature of the wort as quickly as possible. As a general rule, while temps below 105f will probably not kill most yeasts, it is recommended to bring your wort down to 70f or below prior to pitching the yeast, in most cases. However, this range depends highly on the recommended temperature range for the particular yeast this is being used.
Once the wort drops below 165f or so, the danger of infection from various airborne bacteria and stray yeasts becomes a factor. As such, it is important to keep the cooling wort covered as much as possible, and to cool it as quickly as possible. Below are 5 methods used to accomplish this:
In this method, a sink, bathtub or other large tub, is filled with ice and water. The hot kettle containing the wort is then placed in this ice bath until the wort is cooled to the desired temperatures. This method takes the longest and is costly unless you have a large-scale icemaker.
An immersion chiller is comprised of a length of copper tubing, similar to refrigerator ice maker supply lines, formed into a coil, with an inlet and outlet coming out of the top so as to clear the top of the kettle. The coil, after being sanitized, is submersed in the hot wort. One end of the tubing is attached to a hose, and cold water is subsequently run through the tubing. This water absorbs the heat from the wort, and is discharged through the outlet end of the pipe. This is an effective method of cooling the wort quickly.
A simple method of sanitizing an immersion chiller is to immerse the coils into the wort 20 minutes before the end of the boil. This remaining boil time will serve to sanitize the chiller. This will also add trace amounts of copper to the wort, which some claim to be beneficial.
A counter-flow chiller is comprised of one tube that is fed through another, larger-diameter tube. The wort is sent through the inner tube, while cold water is sent the other direction through the outer tube, thus transferring the heat from the wort to the water. This is the most effective wort-chilling method, but is typically more costly and more difficult to clean than immersion chillers.
This chiller works along the same mechanics as a counterflow chiller, but instead of flowing through pipes, the wort passes over a series of plates that are cooled by water flowing through the unit. This is a more water-efficient way of chilling than using a counterflow chiller, but it is far more difficult to clean, as break can get stuck between the plates and be a potential infection issue.
The no-chill method is used by brewers who do not have a chiller or view the use of chillers as being a waste of water (this is of great concern in Australia, which has had varying levels of water restrictions for some years). The wort is racked, generally into a cube or other container and the air removed by squeezing the sides (this requires a plastic container). The wort is left overnight to cool and when it reaches pitching temperature, the wort is aerated and the yeast is pitched.