Why Wort Must Be Rapidly Cooled
As a home brewer one of your biggest concerns is quickly cooling the hot wort. If the cooling process is too slow several problems can develop.
There are proteins in the wort that will cause your beer to haze when it is cold (this is called “chill haze”). Chill haze will not affect the flavor of your beer, but it is considered a cosmetic problem. The only way to remove these proteins and keep your beer looking clear and clean is to cool the wort rapidly, which causes most of the proteins to precipitate and settle out. This is called “cold break.”
Keeping Cold Break Out of Beer
The first step to keeping cold break out of beer is to cool the wort rapidly enough that the proteins precipitate out. An ice bath may or may not do this, but a wort chiller almost certainly will.
An immersion wort chiller will cool the wort rapidly enough to reach the cold break and it will allow the proteins to settle in the brewing kettle. The wort can be siphoned from the kettle, leaving the proteins behind.
Counterflow and plate wort chillers are more difficult to deal with when it comes to cold break. Since the wort passes through these chillers to cool there is not a place for the cold break to settle out until the beer is sitting in the fermenter. To remove the proteins the wort should be recirculated from the ‘wort output’ connection on the wort chiller into the brewing kettle in a fashion that causes it to whirlpool. The whirlpool will force proteins and other debris to the center of the kettle, allowing you to siphon off the wort into the fermenter without any proteins or sediment.
There are two main acids in hops that contribute to the brewing process. “Alpha” acid contributes to the flavor of the beer, while “Beta” acid contributes to the aroma. Alpha acid is released from the hops in boiling water over a long period of time (thus the hour or longer boil while brewing) but beta acid evaporates out in the heat. Hops that are added in the last minute or two of the brewing boil are meant to strictly provide aroma to the beer.
Hop Aroma Problems
Problems arise with hop aroma in beer when a counterflow or plate chiller is used to cool the wort.These chillers only cool part of the wort at any one time, so the hot wort spends extra time sitting in the kettle before it is run through the chiller, allowing more beta acid (and thus hop aroma) to boil off. This is not a problem with immersion chillers because they cool the entire kettle of wort at once.
Preserving Hop Aroma – No Easy Fix
There is not an elegant way to fix this problem. Counterflow wort chiller and plate wort chillers may cool the wort faster overall, but immersion chillers give the entire wort the initial cooling that it needs to prevent loss of beta acid. It is an accepted fact that some hop aroma will be lost when a counterflow chiller or plate chiller is used to cool the beer.
Brewers of lighter beers and lagers may have experienced beer that has the aroma of cooked corn. In wort there are compounds that come from lighter malts which convert to dimethyl sulfide (DMS). The DMS provides the lovely aromas of cooked corn in the beer.
Preventing DMS in Beer
The formation of DMS can be prevented by rapidly cooling hot wort below 140 degrees Fahrenheit. This is easily achieved with most wort chillers, but counterflow chillers and plate chillers cause the same problem as with hop aroma loss. The hot wort sitting in the brew kettle, waiting to run through the chiller, can still form DMS and contribute some of that bad aroma to the beer.
Once again, immersion wort chillers will cool the entire batch of wort below 140 degrees quickly. To discourage DMS buildup in the wort if you are using a counterflow wort chiller or plate wort chiller, it is best to use a pump to move wort through chiller rather than allowing gravity to feed it. Pumps are much more efficient and will get all of the wort cooled faster, even though only a small percentage of the wort is being cooled at any one time.
Have you ever had problems with cold break, hop aroma loss, or dimethyl sulfide? How did you solve the problems in other brews?