Magic Smoke: Cool and Curly Counterflow Chiller

The Magic Smoke Brewhouse is a fine place to chill. Especially since we put together this heat exchange coil for cooling wort.

It's Wort(h) Chilling

Here at Magic Smoke we are very fond of beer — a tasty and refreshing beverage made by fermenting boiled wort. The boiled wort must cool down before the yeast can get going on it. The quicker it can be chilled the better, because while the wort remains hot it is liable to contamination and off-flavours. Dropping the temperature of the wort rapidly also helps eliminate chill haze.

A counterflow chiller is a heat exchanger made from concentric tubes. Wort flows through the inner tube, cooling as it goes. Coolant flows through the outer pipe in the opposite direction becoming progressively warmer. It is an efficient way to chill wort when there is access to plenty of cool water.

Making a Counterflow Chiller

Home brew shops are fun places to go, and will gladly lighten your wallet in exchange for all manner of equipment. Fortunately it's not too difficult to make your own counterflow chiller. The most expensive component is the central pipe which is best made of soft copper refrigeration tubing.

Fortunately we had a coil of copper water pipe salvaged from an indirect hot water cylinder. Its outside diameter was 10 mm which is close enough to 3/8". For the outer jacket we used 25' of 5/8" ID water hose rated to 180°F. After cutting off a few inches off one end of the hose, we could see that the inner lining was black rubber (probably EPDM) bonded to a burst resistant mesh and protective sheath.

The coil was scrap metal and essentially free, but unlike refrigeration tubing it was stiff and prone to kinking when bent. Also it was discoloured and partly corroded on one side. These sections were very resistant to bending. The solution was to anneal them by heating to red hot with a propane torch and allowing the metal to cool. The next stage was to open out the coil little by little, taking care not to kink the coil. We removed the tightest turns, but didn't straighten it completely or the copper would have work hardened to the point where it would have been difficult ever to bend it back into a coil.

The hose was lubricated by pouring soapy water inside, and then pulled slowly over the coil. By trial and error, we found the easiest way to manoeuvre the hose was to stand with the coil over one shoulder. It was a tricky operation and at one point the hose got stuck and had to be pulled back off the coil. As the hose went over the coil it tended to pull it straight and by the time the hose was all the way on, the coil was only 1½ turns. After trimming the hose there was about 8' left over so the coil must have been about 17' long.

Coiling the tubes back up was an even more critical process. Applying too much force at any point would have kinked the copper tube, especially at the annealed sections which were much softer than the surrounding metal. We called a halt after winding the coil back up to the original 7 turns. It didn't seem possible to wind another turn without great risk of ruining the coil.

The next step was to solder T-shaped copper assemblies for the coolant lines (above right). One end of the tee had just a short length of ½" ID copper tube soldered inside, whose OD (5/8") matched the ID of the hose. The other end took a ½" to ¼" reducer: ¼" ID is equivalent to 3/8" OD, matching the diameter of the copper coil. The end stops of the reducing coupling were filed out so that the coil could through the fitting and out the other side. On the side arm was soldered a female threaded adapter to attach a camlock fitting for the coolant lines. (The usual approach is attach the cut off hose fittings and use garden hoses for this purpose.)

In addition, we soldered female threaded adapters to ½" to ¼" reducers so that camlock fittings could be attached to the coil to carry wort in and out (see left).

Soldering these fittings to the coil required a little bit of know-how. Hose clamps were placed over each end of the hose, then the copper fittings were slid onto the coil. The coil was fluxed where the solder joints would be and wet rags draped over the hose and fittings that had already been soldered. Strong heat was applied to solder the coil because the wet rags acted as a heat sink, wicking away heat to protect the materials underneath. After cleaning up the hot solder joints by applying flux and wiping with the rags, all that remained was to pull each end of the hose over the respective tee and clamp it in place. A few cable ties keep the coils in place.

Sanitation is of the utmost importance in brewing. We gave the coil a thorough wash to remove grime and oxidation by recirculating a mixture of hot citric acid solution. Before use the chiller will need to be thoroughly cleaned and then sanitized.