Rapid cooling of the hot wort is needed so that:
The cold break is analogous to the hot break that happens during the boil. By rapid cooling, more protein matter precipitates out of solution and eventually sinks to the bottom of the fermentation vessel with the spent yeast.
A very popular cooling solution for homebrewers, this consists of a coil of small diameter copper tubing (10mm or so) with hose fittings on either end. The device is immersed in the hot wort in the boiler and cold water circulated through the coils.
Immersion chillers are simple and effective and are also easy to make and easy to clean. They are the ideal solution for the home brewer.
With this type of chiller, the beer flows from the boiler tap through a coil of small diameter copper tubing (10mm or so). The tube passes through a section of outer sleeving through which cold water is passed, resulting in the wort coming out of the bottom being chilled to fermentation temperature.
While counterflow chillers are more efficient and can chill to quite low temperatures quickly, they are more difficult to make and can be difficult to clean effectively. Despite that, commercial breweries invariably use counterflow chillers and so do many homebrewers (myself included). A variation of the counterflow chiller is a 'plate chiller' which works in exactly the same way but is much smaller and more compact.
My chiller is home-made and consists of about 20 feet of garden hose with a length of microbore copper pipe shoved through it. Plumbing at the ends allows the hot wort from the boiler to enter the microbore pipe and exit into the fermenter, while cold tap water enters the hose at the bottom and exits from the top into the kitchen sink.
The cooled wort is directed onto a thermometer sitting in a sieve. I set the output temperature to around 22 º C by adjusting the flow of cooling water.
The sieve serves the dual purpose of straining out any hop debris and producing a spraying action which aerates the wort. The system is gravity fed and whole process takes around 40 minutes. The video below shows my chiller in action.
Even with the best brewing set up, you won't get every last drop of wort from the boiler into your fermenter. There will always be a few pints left behind in the hops and 'trub' that remains in the boiler. It is pointless to squeeze the hops in an attempt to retrieve this - you will only succeed in getting trub into your beer.
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