Wort Chilling Techniques

Wort chilling is a simple part of brewing that can have a major impact on your finished beer. The process can be as simple as tucking a brewpot of hot wort into a convenient snowdrift or as complicated as running the wort through a high-tech stainless steel heat exchanger. However you choose to accomplish the cooling process, it is a vital step to achieving the best flavor and appearance of your beer as possible.

Why cooling is critical

There are many important factors to keep in mind as wort makes the transition from the hot side to the cool side. Rapidly cooling wort after the boil facilitates the formation of cold break material, the tiny pale-colored stringy bits of protein-tannin and coagulated protein that slowly sink to the bottom of the kettle as the wort is chilled below 140 °F (60 °C).

Cold break is the same stuff as hot break (which forms during the boil) but the cold break material typically forms in smaller clumps. If the hot and cold break material does not form during either the boiling or chilling process, the uncoagulated proteinaceous material can come back to haunt you later as a haze when the finished beer is cooled below room temperature. Therefore, a vigorous boil followed by rapid cooling of the wort will help limit the potential for chill haze to occur in your glass.

Rapid wort cooling also limits the amount of unwanted volatile compounds such as dimethyl sulfide (DMS) that can continue to be formed from the conversion of S-methyl methionine, a DMS precursor, to DMS while wort is still hot (140 °F/60 °C or higher) but no longer boiling. Boiling drives DMS off in the steam. DMS lends a cooked-corn flavor to beer.

Temperature control

Rapidly chilling your wort will also control what lives and grows in your fledgling batch of beer. Wort must be chilled to get it into the proper temperature range where your chosen strain of yeast can ferment the beer and produce the desired flavor profile for the style of beer being brewed. For ale yeast this is typically 62–75 °F (17–24 °C) and for lager yeast 46–58 °F (8–14 °C).

Lager fermentations may be started around 70 °F (21 °C) and slowly cooled, after fermentation begins, to reduce lag time. Many professional brewers will actually begin a lager fermentation at the coolest end of the temperature range and allow the temperature to rise to what they feel is an acceptable maximum. Cooler wort also allows more oxygen to go into solution during aeration. This oxygen is important for the formation of sterols and unsaturated fatty acids that yeast need to synthesize their cell walls.

Ways to chill

In years past, wort was initially cooled with the aid of a coolship, a large shallow vessel that provided a large surface area for heat to be lost by convection, evaporation and radiation. Once the initial cooling occurred in the coolship, the wort was allowed to flow over a Baudelot cooler, which consists of a set of tubes with cold water flowing through them. This would effectively cool the wort the rest of the way down to fermentation temperatures. This method of cooling allowed DMS to volatize off and the wort to be aerated as it flowed over heat exchange tubes, but also exposed the wort to the open air and a significant risk of contamination.

Most modern-day breweries use some type of heat exchanger where the wort is cooled within an enclosed arrangement with cold water or coolant recovering significant amounts of heat that is used to heat additional brewing or cleaning water.

When I started brewing my first extract-based beers I had very little in the way of equipment, particularly any sophisticated apparatus for chilling wort. As I alluded to earlier, my first wort chiller was a snowdrift outside of my garage. Homebrewers today can use a variety of methods to cool wort, including placing the brew pot in a snowdrift or cold water bath, adding ice to the wort itself, placing an immersion chiller in the brew pot, running the hot wort through a counter-flow chiller or coil placed in an icewater bath, or some variety of plate-type heat exchanger.

I have personally progressed from the snowdrift to an icewater bath, to adding ice directly to the hot wort, to a homemade immersion chiller. My immersion chiller consists of 36 feet (10.8 m) of 1⁄4″ (6.25 mm) inside diameter copper tubing in which I run 52 °F (11 °C) tap water to cool a full-wort boil (5 to 6 gallons/19 to 23 L) down to 68 °F (20 °C) in about 20 minutes.

The table on the previous page lists various wort chilling techniques and the factors of speed, sanitation, cost, and other possible limitations imposed by the brewing environment to help you decide which approach might work best for you.

Methodology and equipment

If you are brewing from extract and not boiling the full volume of wort, the snowdrift, ice-water bath or ice/cold make-up water methods work reasonably well since you are not attempting to cool a full 5-gallon (19-L) volume of wort. A less-than-full-wort boil leaves room to add cold water or ice to both cool the wort and bring it up to full batch volume. To cool wort using either the snowdrift or ice water bath methods; simply place the brewpot of hot wort in the snow or water bath being careful to not let the pot tip or float (and spill any of the wort) or allow any snow or water to enter the brew pot. Leaving the lid off of the pot will hasten wort cooling by convection and evaporation, but will greatly increase the risk of contamination. The snowdrift or ice-water bath methods of wort cooling are effective, but can also be slow. They also provide greater opportunity for contamination and the accumulation of DMS in your brew. (Read “Beginner’s Block” on page 12 for more about chilling wort for stovetop).

Immersion and counterflow chillers or other types of heat exchangers work well whether you are performing a full or partial-wort boil. These types of chillers all need to be sanitized before use. An immersion chiller is sanitized by simply placing it in the brew pot during the last ten minutes of the boil. An immersion chiller is a coil of copper or stainless steel tubing usually between 25 and 50 feet (7.6 to 15 m) long. After the boil is complete and the heat source turned off, cold water is run through the coil, picking up heat from the wort. A variation on this concept involves supplying water from a container with ice floating in it, and continuously recirculating the water to cool the wort. This method uses less water than a flow of water directly from the tap. (See the “Projects” column “D.I.Y. Wort Chiller – Turn an immersion version into a recirculator” by Forrest Whitesides in the December 2007 issue of BYO). An immersion chiller is easier and less expensive to build than a counterflow chiller, and is easier to clean by simply scrubbing the outside surface of the coil.

Since an immersion chiller sits directly in the brew pot, both the hot and cold break material settle to the bottom of the pot and are left behind when the wort is drained or siphoned into the fermenter. This leaves most of the break material and hop residues (collectively referred to as trub) behind in the brewpot. Additionally, an immersion chiller can be gently swirled to stir the wort and increase the volume of wort that comes into contact with the coils to speed the cooling process. This can also create a whirlpool that helps to concentrate the trub in the center of the pot away from the outflow valve.

Counterflow or plate heat exchangers can be sanitized either by running boiling water through the chiller for 30 to 40 minutes or flushing the chiller with a sanitizing solution followed by a potable/sanitized water rinse (if the type of sanitizer used requires rinsing). If your chiller is made of stainless steel you should not use bleach as a sanitizer as it may lead to corrosion of the metal surfaces.

A counterflow chiller consists of a tube within a tube, often copper tubing within copper tubing or copper tubing within rubber or vinyl garden hose. The outer tube is enclosed around the inner tube with fittings on each end that allow water to flow through the outer tube in one direction while hot wort runs through the inner tube in the opposite direction, hence the name counter-flow. In this manner the hot wort must pass by an oncoming flow of cold water creating a very high volume of cold water to hot wort interaction. Some of the newer counterflow chillers have coiled or otherwise convoluted inner tubes or inner tubes with fins to increase the surface area for heat exchange. A variation of the counterflow design allows the hot wort to flow through a coil of tubing placed in an ice water bath. This method requires the use of ice, but uses less water than a typical counterflow set up.

A counterflow chiller is more difficult and expensive to build than an immersion chiller and the user must be very diligent about cleaning the chiller after use. A counterflow chiller should be rinsed with hot water and cleaning solution (such as Powdered Brewers Wash) immediately following use to be sure the inside coil (where the wort flows) is clean prior to the next application.

Another slight disadvantage of a counterflow chiller is that development of some of the cold break material occurs within the chiller and is subsequently delivered to the fermenter instead of being retained in the kettle with the rest of the trub. There is continuing debate among brewers as to the effect on beer flavor of excessive trub in the fermenter. Some trub in the fermenter provides nutrients necessary for healthy yeast, while an excessive amount of trub can lead to off flavors.

Advantages of using a counterflow chiller are that it cools the wort very quickly and a hopback may be placed between the brewpot and the chiller. This can increase hop flavor and aroma in the wort and help filter out trub that may flow from the kettle. Using a hopback is not as practical when using an immersion chiller as the wort is cooled before it leaves the kettle. Use of a hopback in combination with an immersion chiller would necessitate some sort of intermediate vessel (often called a grant) between the hopback and fermenter where the immersion chiller would have an opportunity to cool the wort in the grant before being delivered to the fermenter.

If you live in a relatively warm climate, the tap or ground water used for cooling in an immersion, counterflow or plate heat exchanger may not be very cold (warmer than 60 °F or 15.5 °C). If this is the case, a water pre-chiller becomes necessary. A pre-chiller will cool the water down enough to be effective before it runs through the wort chiller. Pre-chilling cooling water can be accomplished by placing a coil of tubing in a bucket of ice-water in the line supplying water to the wort chiller. Even in a cold climate like mine (North Dakota) where a pre-chiller is not necessary, I have laid the hose supplying water to my immersion chiller in a snowdrift for increased chiller effectiveness.

Wort chilling may be a relatively simple part of the brewing process, but its effect on beer flavor and appearance is critical. Choose a wort chilling technique that suits your brewing environment and budget to help you accomplish this important step in making better beer.

Issue: March-April 2008