What is Hot Cubing? No Chill Brewing

All grain brewers finish off the all grain brewing process by bringing the collected sugary wort to a boil for 60 minutes. This allows the brewer to add bitterness through the addition of hops, remove DMS and pasteurise the wort, leaving a sterile environment for the yeast to ferment without allowing other microorganisms to ferment the wort which could produce off flavours. At this point various methods are used to quickly cool the wort down to a temperature that is suitable for a brewers yeast to be pitched. Typical methods of cooling the wort at home involve counterflow chillers or immersion chillers which use tap water to remove heat from the boiled wort.

In cool climates these chillers are effective at quickly cooling the wort. Unfortunately Australia's sweltering heat means our groundwater can exceed temperatures of 30°C. A counterflow or immersion chiller can only cool the wort to within 5-10°C of the ground water that is being used to cool the wort.  This means the average homebrewer will then have to use a fermentation fridge to cool the wort another 10°C+ to yeast pitching temperatures. This process can introduce a risk of infection as temperatures in the mid 30°C are a prime breeding ground for bacteria. This is where hot cubing can be used as an effective cooling system. 

Instead of using any counterflow or immersion chiller the boiling wort is transferred into a clean hot cube as soon as the boil finishes. The cube is then filled completely to eliminate any dead space in the cube and sealed to cool naturally as it radiates heat over the next hours. Since the wort enters the clean cube at 100°C the internal surfaces of the hot cube are pasteurised with the boiling temperatures giving rise to an aseptic environment until the cube is opened. The benefit of hot cubing is as long as the cube is clean before use and the wort enters at boiling temperatures the liquid inside the cube will stay aseptic until the cube is opened; which normally wont happen until the wort has cooled sufficiently and is at pitching temperature. This also offers a great solution to time poor brewers as the time taken to fill a hot cube is substantially less than it would take to use a chiller.

There are some considerations to take into account when hot cubing. The first is ensuring to thoroughly clean the cube before use. Failure to do so can lead to a buildup of material on the internal surface of the cube which could potentially harbour bacteria or yeast that may not be pasteurised with the boiling wort. Using a good quality cleaning product such as PBW, Sodium Percarbonate or an Alkali Salt mixture will ensure any buildup is broken down and the cube is adequately clean before use. Clean the cube thoroughly after adding the contents to your fermenter to stop mould or bacteria growing inside the cube between batches.

The second consideration pertains to bitterness. Bitterness is a result of Alpha Acids in hops isomerising in hot wort. Temperatures above 80°C are much more effective at isomerising alpha acids. Since the wort will spend a substantial amount of time above 80°C inside the cube the wort will continue becoming more bitter. To avoid beers coming out overly bitter you may want to decrease the amount of hops added late in the boil which could substantially increase the IBU's in the wort. Cooling the cube as quickly as possible to below 80°C will also help to minimise the unintentional bittering of the wort. If you have a pool throwing the cube in the pool will drastically speed up the rate of cooling.