Wort Chilling

This month's question: Why do I need to chill my wort quickly? What types of equipment are available for chilling?

Answer: One of the things that most homebrewers are first taught is that is important to chill your wort quickly. There are several reasons for this:

To minimize the risk of bacterial infection. If you just let your wort cool naturally, it will cool fairly rapidly at first. It will slow down once it approaches room temperature, though. This means it will spend a lot of time in the range of "moderately warm". Under these conditions, many types of bacteria can breed rapidly. They will love nothing better than a pot of ready-made sugar solution, complete with protein and other nutrients. By the time it has cooled to the point where you can pitch yeast, a raging infection might have already taken place.
To minimize dimethylsulfide production. Dimethylsulfide, or DMS, is a compound that forms while wort is hot. While boiling, it is driven off with the steam. It builds up in hot, but not boiling wort, and cannot form in cool wort.
To improve cold break. A number of proteins precipitate out of solution while wort cools. Rapidly chilled wort forms bigger chunks of this protein, making it easier to settle out during subsequent racking.

The bottom line is that you will make better beer with rapidly cooled wort. The simplest method of chilling wort is to put your boiling kettle in the sink at the end of the boil. Fill the sink with water, so that no water gets inside the kettle. One of the double-sided sinks is best, so that you can let the water continue to run and overflow into the empty side and down the drain. Stir the wort with a sterilized spoon to increase the cooling rate. I know of one guy who uses his swimming pool instead of his sink. Another guy in Pennsylvania uses a snowbank.

A more elegant approach is to get an immersion wort chiller. This is a copper coil with fittings that you can hook up to tap water. It fits into the kettle, and provides a considerable amount of surface area for heat transfer. Stirring isn't required with a wort chiller, but is works faster if you do. You need to make sure the chiller is sterile before stuff gets cold. The simplest method is to drop it in the boiling kettle about 10 minutes before the end of the boil. Immersion chillers are simple to use because there is not doubt about if they are clean, and they rarely have any flow problems.

The top-of-the-line cooling method is a counterflow chiller. These are a bit more complicated, but they make the most efficient use of cooling water. Your brewing setup will either need to have room below for gravity draining, or else you need a hot wort pump. Three plumbing connections are needed, with the fourth typically draining straight into one of your fermenters. The inside coil of the chiller needs to be sterilized before attaching it to the boiling kettle spigot. Some people will flush hot wort through to sterilize it, though this results in a loss of wort. One critical extra thing needed is a strainer on the inside of the wort spigot to strain out hop leaves, unless you have used a hop bag. Counterflow chillers are subject to plugging if the strainer gets plugged, or it is comes loose, letting hop leaves into the coil. This can be bad news, since you will inevitably risk infecting your wort while you try to clean it out. If you go with a counterflow chiller, make sure you understand its workings with a practice run before brew day.
Whatever method you use to cool your wort, you're sure to find that the beer is cleaner tasting and has better clarity, so the extra effort really pays off.