• Control within + - 1 degF.
• Cooled by either ice or by a heat exchanger in the brew fridge
• Small foot print when in use and easily stored when not.
• Doesn't eat alot of ice.

The Heat Exchanger
The guts of the gizmo is the heat exchanger inside the keg. It's made from a 3' corrugated stainless steel connector that's intended for connecting gas to gas appliances. I got it at Home Depot. Hack the fittings off of the ends leaving as much of the uncorrugted tubing as possible. Assemble as shown in the detail above and solder with Stay-Brite silver-like solder (available at hobby shops). The fit between the connector and the coupling is a bit looser than what I like, so I enlarged the ends of the SS connector with a swaging tool. The compression fittings in the keg disconnect posts allow the heat exchanger to be fitted inside the keg and allows for removal for cleaning. Drill out the compression fitting so tthe 1/4" copper tube will pass through. Turn down the MPT end of the fitting so that it's a friction/interference fit inside the keg disconnect post. I used a "vertical lathe" for this (a.k.a. a drill press and a file). For one keg, I heated the post to enlarge it then pounded in the fitting. For another keg I used LockTite. Both have held up well. Use delrin rather than brass inserts in the compression fitting and don't torque down the compression nut too tight or the heat exchanger won't be easily removable! (I'm now using 1/4" SS tubing since it isn't dented by the compression fitting.)

Hacking the Keg Lid

The fittings indicated in the above drawing are all mounted via tapped holes in the lid. Allow for enough space between them for a wrench on the 1/4 fittings and a socket on the larger fitting and use telfon tape on each fitting. Don't over-torque the fittings or they will strip- particiliarly the larger one since there's not a lot of thread engagement. I did a mostly-hydro pressure test to 20 psig after assembly by filling the keg almost completely full of water, pressurizing slowly with CO2 and then soap testing the joints. I've not shown it, but I also modified another keg lid as above but used a 1/2" hard tubing fitting to allow a bigger cross-sectional area for blow-off.  Rather than tapping the lid, I soldered the fitting to the lid with Stay-Brite solder after peening over the end of the fitting on the inside surface of the lid. The temperature probe is a thermistor at the end of a 6" length of 1/4" copper tubing (it's now stainless tubing).  The business end of the thermistor is exposed and the gap between it and the tubing is sealed with silicone sealant. The racking/sampling port has a length of 1/4" tubing installed during fermentation. It's used for taking samples for s.g. testing and evaluation. Like the compression fittings on the keg, both of the above ports use delrin compression inserts and the compression nut isn't torqued too tight.   It can be replaced with a longer piece of tubing for racking, but, unless you pressurize the keg with CO2, it makes for slow racking due to the small ID of the tubing. I usually remove the elbow attached to the blowoff port and drop in a racking cane. The blowoff port is fitted with an elbow with a short lenght of vinyl tubing overlapping the joint. A longer length of vinyl tubing is fitted to the end of the elbow. If I was doing the lids again. I'd go with the 1/2" hard pipe fitting soldered in the lid for the primary fermenter and maybe a 1/4" elbow for the secondary fermenter. Eventually, I'll replace all of the copper and brass fittings and tubing on the lid and the two fittings on the keg disconnect posts with stainless steel to avoid any dielectric corrosion. So far (6 batches), this hasn't been a problem. The hassle with the lid is that you have to sung it place on the keg and then attach the temp. probe, sampling and racking tubes and blowoff. When filling from the boiler, I rack in via the blowoff opening and have foam stoppers on the other openings for air venting.

Keg Insulation
The keg has an insulative jacket made of 3.5 layers of ordinary sleeping pads (about 5/8" thick from WalMart).  Foam carpet padding can also be used and it's a lot cheaper than sleeping pads.  Can't remember how many pads were used but they were taped together at the ends and wrapped around the keg with a some paper temporarily plcaced between the keg and jacket so that the jacket is a bit larger than the keg OD- that way, the jacket can be easily slipped on and off.. The jacket is covered with aluminiized bubble wrap. The later cuts down on radiant heat transfer (and it gives a NASA like look that's cool). The jacket is sealed tight against the top of the keg with a hose clamp (actually it's 2 long hose clamps jointed end-to-end). The two "ears" at the top of the jacket are made from regular duct tape secured to the projecting layer of sleeping pad for easy removal of jacket. All raw edges are covered with aluminum (not fabric) duct tape. Here's a drawing with the details:

• Wire the controller to my PC for data logging
• A heater for fermenting in the garage in winter.
• Hack the controller so it controls the brew fridge also.
• Add a gizmo to measure the rate of evolution of CO2 during the ferment. Best brain-fart so far is:


When the fluid in the smaller diameter tube overflows via bubbles from the overflow, the probes on the fluid sensor detect the brief rise in the level of fluid. If this doesn't work, maybe a microphone connected to a filter and flip-flop circuit to detect the "glugging" sound. The spikes from either device can be counted and the off-gas rate calculated by the Stamp.
• If there's enough program memory left in the Stamp after all of the above (doubtful...), add programming for automatically changing the temp. setpoint so that it can automatically do dicetyl rests and automatic drops to lagering temps.