Wort chillers are devices used to speed the cooling of hot wort from boiling temperatures down to a safe temperature to pitch yeast. Yeast usually must be pitched at under 80F, more commonly in the 65F - 70F range. The common concept behind wort chillers is running cold water and hot wort in close proximity to each other, but separated by heat conductive material.

Wort chillers are not strictly necessary, as you can simply use an ice bath, or use the no chill method, but most brewers who perform full boils (>5 gallons) depend on wort chillers.

The two most commonly used wort chillers are immersion chillers and counterflow chillers.

An immersion chiller is simply a coil of copper pipe. Common lengths are 25' or 50' of 3/8“ or 1/2” flexible, soft copper tubing. The tubing should be thin, either type M or type DWV (wall thickness in the .02 - .03 range). The tubing is wrapped around a corny keg or paint can to form a coil, and bent to provide an inlet and outlet at the top. The entire coil is placed into the brew kettle, and then cold water is fed through the chiller.

Water can be fed by connecting to a sink, garden hose, or pump. The water can be chilled additionally by using a prechiller, which is a second coil of pipe placed into ice water. Water flows out of your hose, into the prechiller, into the wort chiller, then out to a drain.

Immersion chillers are significantly more effective than ice baths or waiting for the wort to cool, but they suffer from local conductivity problems. The wort near the coil cools very quickly, but the wort not in direct contact cools much slower. To increase the effectiveness, the wort can be whirlpooled manually or with a pump, or the chiller can be moved around in the wort. If using a prechiller, the same must be done in the ice water.

An immersion chiller is very simple to build yourself with a coil of copper, some silicone tubing, and a few clamps.

Counterflow chillers are the most effective means for cooling wort. With a counterflow chiller, the wort itself is pumped into a metal chamber, and either recycled back into the kettle or pumped straight into the fermenter. Simultaneously, cold water is pumped into an outer chamber flowing in the opposite direction of the wort. The surface area of cold water to hot wort is maximized, resulting in extremely fast cooling.

Counterflow chillers can be larger than immersion chillers if designed as a small copper tube within a large copper tube, or very compact when designed as a series of welded metal plates with tight channels. Tube-within-a-tube models are comparably priced with immersion chillers (and can be built at home), but the metal plate models tend to me more expensive and hard or impossible to build yourself.

One drawback of counterflow chillers is they are difficult, though possible, to use in a gravity-fed setup. Most brewers who use counterflow chillers use a pump to move the wort, which results in a higher cost and more items to clean. Additionally, cleaning a counterflow chiller is more difficult, and an improperly cleaned chiller can be a source of infection.

Copper is known to leach metallic off-flavors into beer if not cleaned properly. It is recommended that any new copper be boiled until the shiny surface becomes dull before allowing it to contact wort. Additionally, periodic cleaning with a light vinegar solution will help maintain its condition.

For more information, see the metallurgy page.

Since cold wort comes in contact with the chillers, they must be properly sanitized.

For immersion chillers, this is usually accomplished by placing the chiller in the wort during the last 5 minutes of the boil. The temperature sterilizes the chiller. The hose connection should be checked for leaks, as the water may not be sterile and there is potential for infection if water drips from the connections into the wort.

For counterflow chillers, the risk for infection comes from particles getting stuck in the chiller. Since post-boil wort contains trub sediment, proteins, grain and hop material can get stuck in the counterflow chiller and harbor bacteria. Brewers generally flush counterflow chillers very thoroughly with brewery cleaner products, followed by a backwash (flow cleaner in the opposite direction) to dislodge as much as possible. The chillers should also be sanitized before use.