Cooling, Racking, and Aerating

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There are a few steps required to get the wort ready for pitching the yeast and fermentation:

  1. The wort must be cooled to a temperature low enough that it will not kill the yeast
  2. The wort must be transferred from the brew pot into the fermenter
  3. Enough oxygen must be introduced into the wort to allow for efficient fermentation

This article explains why and how each of these intermediate steps is performed.

Cooling, Racking, and Aerating for the Beginning Homebrewer

Each of these three steps can be done with expensive, specialized equipment although it is not necessary for the beginning brewer. There are cheap and simple, and effective methods for each; some of which are still used by many more advanced brewers. In some cases, the high-tech methods may actually be less effective.

Cooling for the Beginning Homebrewer

Assuming the brewer's first batch will be a partial boil batch on a kitchen stove, with a total volume of two or three gallons, the easiest way to cool your wort is with an ice bath. When the boil ends, place the brew pot in the kitchen sink, then fill the sink around the brew pot with a mixture of crushed ice and water and leave it there until the wort is cooled to approximately 80°F. The cooling can be expedited by stirring gently with a sanitized spoon, being careful not to splash or agitate the wort which might introduce oxygen.

Racking for the Beginning Homebrewer

The Beer Brewing Process
1. Preparing the Ingredients
2. Cleaning and Sanitation
3. Making the Wort
4. Boiling the Wort
5. Cooling, Racking, and Aerating
6. Pitching the Yeast
7. Primary Fermentation
8. Conditioning the Beer
9. Packaging and Carbonation
10. Dispensing and Serving

Racking or siphoning is a system of transferring liquid from one vessel to another through a series of gravity-fed tubes. Essentially, it provides a way to get liquid to travel up a tube and out of one vessel, then back down and into another.

The equipment sold with most beginning brewing kits eliminates the need for racking and siphoning. Assuming the primary fermenter is a plastic bucket fermenter and the brewer is only doing a partial boil of a few gallons of wort, simply pick up the kettle of cooled wort and carefully pour it into the fermenter bucket.

If using a carboy as a fermenter, the wort can be carefully poured into a sanitized funnel. If it's a full wort boil, however, read the section on racking and siphoning below.

Aerating for the Beginning Homebrewer

While introducing oxygen to hot wort is bad, yeast needs oxygen to thrive, and fermentation will go more smoothly if oxygen is introduced into the cooled wort before pitching the yeast.

The simplest method, and one of the most effective, is to simply shake the wort. Pick the fermenter up, put the lid on tightly, and shake it vigorously. This can be done with a partially full fermenter and then filled with the rest of the liquid if a full fermenter is too heavy (45 lbs.).

Some beginning homebrew books advise you to aerate the wort by pouring the cooled wort into the fermenter from a height. However, wort aeration is important enough that a little bit of extra shaking would still be a good idea.

Cooling, Racking, and Aerating for the Advanced Homebrewer

Eventually, most homebrewers start doing a full-wort boil, boiling five gallons (or more) of wort in a larger brew pot. This increased wort volume requires a few extra steps, and in some cases extra equipment, to prepare the wort for pitching.

Cooling the Wort

Cooling the wort quickly is important to avoid both oxidation or staling and infections, and five gallons or more of wort doesn't cool quickly in a simple ice bath.

See the main article on cooling wort for a discussion of why cooling is important and a discussion of the different types of chillers available to the home brewer.

Racking and Siphoning

Various methods for transferring the wort to the fermentation vessel can be used. The object here is to leave behind as much of the solid hot break material, as well as hops and any other solids. Once cooled, the wort is either poured or racked into the sanitized primary fermentation vessel. While not absolutely necessary, it is highly recommended that brewers strain their wort to some degree prior to fermentation. The hot break solids and hop debris can lend tannins and off-flavors to the beer, and it is best to remove as much of it as possible.

Typically, the cooled wort is poured, racked, or pumped from the kettle into the primary fermenter. During this process, various straining methods are utilized. These include:


As the wort is cooling, it is stirred in a circular motion with a large sanitized utensil. This creates a whirlpool effect, which concentrates many of the solids in the center of the pot (where they eventually settle out), allowing for easier racking.


In the hop-back method, the cooled wort is sent through a filter, such as the false bottom in the mash tun, leaving behind the hop leaves. The bed of leaves also acts as a filter for some of the other solids.


A standard piece of equipment for homebrewing is the funnel. It is large enough to accommodate pouring, and comes equipped with a removable fine screen. With funnel straining, the wort is poured or racked into the funnel, which is placed in the neck of the primary carboy, or on the side of the primary bucket. Since the strainer tends to get clogged fairly easily, it is often a good idea to filter the wort through a larger-scale filter (such as the hop-back method) prior to sending the wort through the strainer. In all likelihood, with most beers, the brewer will also have to constantly stir the strainer (a sanitized butter knife or spoon works well) while scraping the screen in a circular motion. This continually agitates the solids on the screen, which allows liquid to pass through.

Aerating the Wort

During the boiling process, most of the oxygen is removed from the wort. In order for your yeast to achieve an optimal healthy metabolic rate during fermentation (generally resulting in higher attenuation levels and a healthier overall fermentation), the brewer must re-introduce oxygen into the wort prior to fermentation. While not absolutely necessary, this practice is highly recommended.

It is important that the wort be allowed to cool to pitching temperatures prior to deliberate aeration. In order to cut down on lag time, some brewers may opt to pitch the yeast prior to aeration.

There are several methods by which aeration is accomplished:

  • When doing partial-boils, unboiled (and thus, still oxygen-rich) water is added after the boil, thus introducing oxygen back into the wort. However, this alone is typically not adequate.

  • When straining the wort from the kettle into the primary fermenter, the splashing and agitation that occurs introduces some oxygen back into the wort. However, this alone is typically not adequate.

  • After the wort has been transferred to the primary fermenter, the brewer can seal the vessel and shake it vigorously. While this method is used alone by many brewers, it is typically less reliable and efficient than mechanical aeration/oxygenation.

See Also:

Mechanical Aeration

Most homebrew supply shops sell aeration kits specifically designed for wort aeration. They are comprised of an air pump, an in line air filter, and vinyl tubing with an aeration "stone" on the tip. Alternately, brewers may opt to build their own aeration kits using fish aquarium parts. The pump is turned on, forcing air through the lines, while the sanitized aeration "stone" is placed in the cooled wort; the stone diffuses the oxygen and aerates the wort. 20-60 minutes is typically adequate using this method.

Mechanical Oxygenation

Similar to mechanical aeration, many homebrew supply shops sell oxygenation kits. The advantage of oxygenation kits is that the time required to introduce adequate amounts of oxygen into the wort is reduced to 15 minutes or less. The disadvantage is that these kits require the brewer to purchase bottled O2 from the hardware store.

What do I do next?

Once the cool, aerated wort is in the fermenter, you are ready to move on to the next step in the beer brewing process: Pitching the Yeast.