Boiling and Cooling
Cooling the Wort
At the end of the boil, it is important to cool the wort quickly. While it is still hot, (above 140°F) bacteria and wild yeasts are inhibited. But it is very susceptible to oxidation damage as it cools. There are also the previously mentioned sulfur compounds that evolve from the wort while it is hot. If the wort is cooled slowly, dimethyl sulfide will continue to be produced in the wort without being boiled off; causing off-flavors in the finished beer. The objective is to rapidly cool the wort to below 80°F before oxidation or contamination can occur.
Rapid cooling also forms the Cold Break. This is composed of another group of proteins that need to be thermally shocked into precipitating out of the wort. Slow cooling will not affect them. Cold break, or rather the lack of it, is the cause of Chill Haze. When a beer is chilled for drinking, these proteins partially precipitate forming a haze. As the beer warms up, the proteins re-dissolve. Only by rapid chilling from near-boiling to room temperature will the Cold Break proteins permanently precipitate and not cause Chill Haze. Chill haze is usually regarded as a cosmetic problem. You cannot taste it. However, chill haze indicates that there is an appreciable level of cold-break-type protein in the beer, which has been linked to long-term stability problems. Hazy beer tends to become stale sooner than non-hazy beer. The following are a few preferred methods for cooling the wort.
Place the pot in a sink or tub filled with cold/ice water that can be circulated around the hot pot. As mentioned in the previous chapter, it is best to keep the pot lid on, but if you are careful you can speed up the cooling by stirring. Gently stir the wort in a circular manner so the maximum amount of wort is moving against the sides of the pot. Minimize splashing to avoid oxidation. Don't let water from your hands drip inside the pot; this could be a source of contamination. If the cooling water gets warm, replace with colder water. The wort should cool to 80°F in about 30 minutes. When the pot is barely warm to the touch, the temperature is in the right range.
People often wonder about adding ice directly to the cooling wort. This idea works well if you remember a couple key points.
- Never use commercial ice. It can harbor dormant bacteria that could spoil your beer.
- Always boil the water before freezing it in an airtight container (like Tupperware). It must be airtight because most freezers also harbor dormant bacteria.
- If the ice will not directly contact the wort, (i.e. you are using a frozen plastic soda bottle or other container in the wort) make sure you sanitize the outside of the bottle first before you put it in the wort.
Copper Wort Chillers
A wort chiller is coil of copper tubing that is used as a heat exchanger to cool the wort in-place. While wort chillers are not necessary for your first batch of beer, especially when you are only boiling 2-3 gallons, this is a good time to make you aware of them. Wort chillers are useful for cooling full volume boils because you can leave the wort on the stove instead of carrying it to a sink or bathtub. Five gallons of boiling hot wort weighs almost 45 pounds and is hazardous to carry.
There are two basic types of wort chillers: immersion and counter-flow. Immersion chillers are the simplest and work by running cold water through the coil. The chiller is immersed in the wort and the water carries the heat away. Counterflow chillers work in an opposite manner. The hot wort is drained from the pot through the copper tubing while cold water flows around the outside of the chiller. Immersion chillers are often sold in homebrew supply shops or can be easily made at home. Instructions for building both types of chiller are given in Appendix C.
Barchet, R., Cold Trub: Implications for Finished Beer, and Methods of Removal, Brewing Techniques, New Wine Press, Vol.2, No. 2, 1994.
Fix, G., personal communication, 1994.