Photo of disassembled cap

I use it with either an  small CO2 inflator (below) or a simple air pump when the brew in the keg will be consumed in a day or less (any longer and the brew will get oxidized and taste terrible).  The CO2 inflator uses the high pressure of a small, 12 gram CO2 cartridge.  The downnside is that the cartridges are a bit expensive.  The inflator is real handy for traveling tho'- especially if your CO2 source is otherwise a 20 pound CO2 cylinder!

Caveats

• Don't use damaged pop bottles- they could rupture.  I've never had one to do so, but have discarded some questionable ones.
• Pressure test (below) the rig before using.
• Don't plan on storing brew in the mini-kegs for much longer than a month or two assuming you keep them cold. YMMV with delicate brews and warmer temps.   Long term storage is said to cause the brew to become oxidized since the PET plastic the bottles are made of is not a good O2 barrier. Yes, the CO2 pressure in the bottle after filling is much greater than atomspheric pressure, but, as counter-intutive as it seems, oxygen will still pass through the plastic.

The only problem I've had with the depressors is the small o-ring in the end that attaches to the access fitting will somethimes fall out.  I just keep a male flare fitting handy and screw it into the end when it's detached from the access fitting- this retains the o-ring..

1. Use one of the "blocky" type street elbows- they afford more surface area for soldering in the beer tube.  A street elbow has both a male and female outlet while a regular elbow has two female outlets.  The downside is that the nut won't run up tight against the washer/cap/gasket.   To remedy this, either 1) chase the male threads  (i.e. using a threading die turned around "backwards" on them) or 2) use additional washers to take up slack between the nut/washer and the cap.
2. First drill a 7/32" hole completely through the elbow from the 1/8" MPT end then enlarge with a 1/4" drill BUT don't drill completely through the elbow!   This is shown in the drawing above.  A drill press/vise is good for doing this since the bit will tend to grab and hence increase the chance of drilling to deep.
3. The 7/32" OD brass tubing is avaible in 1' lenghts at any decent hobby store and at some hardware stores.   Install the tube and the washer and solder them to the elbow.  Clean the joint areas first and use lead-free solder.  Be sure to remove all flux after soldering.
4. Saw off any tubing that comes on the 1/8" MPT end of the access fitting and screw into the elbow using teflon tape.
5. If the nut doesn't run up far enough on the male end of the street elbow, either  1) reduce the size of the male threads by using a threading die "backward"  or 2) use multiple  washers to take up slack between the nut/washer and the cap.  Don't try to enlarge the threads on the nut while holding it in a vise- it'll likely deform during the process.
6. The 3/16" ID vinyl dip tubing in the bottle is whacked off via  two 45 deg. cuts-  the end is shaped like ">".  A single-cut end may come to rest against the bottle and cause dispensing problems.
7. To prevent the 3/16" ID vinyl dispensing tubing outside the keg from getting detached from the cap (results in a beer geyser!), secure it with a couple of nylon tie wraps or or wrap wire over it.
8. Don't sweat finding a washer with the precise ID hole to match the male end of the streat elbow-  shoot for "too small" and enlarge the hole with a rat-tail file.
9. Cut your own gasket rather than trying to find/buy one the correct size.   I use /16" red rubber gasketing material purchased from my local Ace Hardware store.

Surface Lead Removal
If you are concerned about getting lead in you brew from the brass tubing, remove any lead on the surface of the fitting by following John Palmer's lead removal method:

A solution of two parts white vinegar to one part hydrogen peroxide (common 3% solution) will remove tarnish and surface lead from brass  parts when they are soaked for 5-10 minutes at room temperature. The brass will turn a buttery yellow color as it is cleaned. If the solution starts to turn green and the brass darkens, then the parts have been soaking too long and the copper in the brass is beginning to dissolve, exposing more lead. The solution has become contaminated and the part should be re-cleaned in a fresh solution.

Hydro Test
After assembly, do a hydro test on the assemblied keg. Don't skip the "hydro" part and use just air or co2- it's a safety thing. If something ruptures during the test with water filling the bottle, less energy will be imparted to targets in the blast zone since water is practically imcompressible- OTHO, there's lots of energy in a compressed gas.  Fill the bottle with water and secure the top to the bottle. Pressurize with air or co2.    I use 20 or so psig but once took a plastic 3L bottle up to my water tap pressure (55 psig) without any problem. You'll note that the bottle expands a bit and there is a bit of air or co2 atop the water in the bottle. This violates my advice on hydro testing but it's only a little gas space and it's actually a good thing since air or co2 will escape through any leaks more readily than water would. Assess leakage by applying a soap/gylcerine solution or submerging in a water bath and watching for bubbles.

Preserving the brew's carbonation during the filling operation isn't as critical as it is when filling bottles since the carbonation can be "topped-off" by applying co2 via the mini-keg cap.  When I'm filling more mini-kegs than I have keg tops, I cap the bottles with unmodified plastic caps then replace this cap with a keg top and top up the pressure.  Flat brew or pop can also be force carbonated in 3L using either the tap cap or a cap fitted with a metal air stem.

I used to fill the bottles from a corny keg with a counter-pressure filler.    A caution tho': if your experience with counter-pressure filling is limited to regular glass bottles, be prepared to use ~3 times more force to hold the filler on the larger diameter 3L bottle tops when co2 pressure is applied!

There are two faster and easier ways to get brew from a cornie keg into a mini-keg:

FAST/EASY:  This method is basically counterpressure filling by connecting the cobra taps on the minikeg and cornie keg together using a bit of 3/8" OD vinly tubing fitted over their snouts.   I usually relieve co2 pressure in the minikeg by simply loosening the minikeg's cap.   A brief description:   Connect the snout of the cornie and a sanitized and purged/sanitized  mini-keg together, connect both kegs a source of regulated co2, open the co2 valve at the regulator and loosen the cap on the mini-keg to allow the co2 to further purge the bottle,  tighten the cap on the mini-keg to pressurize the bottle,  latch open both of the the cobra taps,  barely loosen the cap on the mini-keg to allow the brew to flow into the mini-keg and control the flow by adjusting how much the cap is loosened and fine-tune by pressing down on the cap, when just about full, tighten the cap on the mini-keg to stop the flow of brew, close both cobra taps (this is very important- don't ask how I know! :-)   and disconnect the taps.   This is MUCH faster and easier to do than sanitizing and connecting up the counter-pressure filler.  In fact, I can fill a mini-keg about as quickly as it took me to write the above!

FASTEST/EASIST-  Where the brew will be consumed without much delay, simply fit a 1' or so length of 3/8" ID vinyl tubing to the snout of the cobra tap from the cornie keg, place a (maybe purged- more below...) 3 liter bottle at a lower elevation that the cornie keg, reduce the co2 pressure in the keg a bit by cracking the pressure relief valve, open the cobra tap fully to fill while adusting the co2 pressure regulator to adjust the flow of brew into the bottle.   You'll loose more carbonation than with the above method, but, it can be restored by force-carbonating.   I seldom bother anymore purging the bottle with co2 before filling.  Instead I "cap on foam"- withdraw the end of the filler when the bottle is about full and fill the headspace with foam by cracking open the cobra tap.  The foam will displace residual air in the bottle.

If you want to use use a co2 powered pocket tire inflator gizmo for dispensing, you'll need an adapter to fit it's tire valve end to the minikeg.   Remove the rubber from tire air stem.  That'll leave a brass tube exposed.  Fit and solder it onto a flared  piece of copper tubing with female flare nut attached.  The later attaches to the thumbscrew core depressor.

Better yet, add a 0-60 psig tire pressure gauge between the inflator and the depressor so the mini-keg pressure can be determined. Here's a drawing of how I did it.

The end of the 1/8" NPT pipe cap has a half-round slot filed in it too match the OD of the tire air stem.  A hole is drilled in the air stem and, if needed the filed end of the pipe cap.

WARNINGS- if you don't open the access valve before applying pressure, the pressure gauge will be pegged and ruined (don't ask how I know this :-).   Even worst, the gauge could explode.  The reason for this is the inflator has no pressure regulator.  When using the inflator, just apply the co2 in very breif bursts- especially when the minikeg is full of brew!  A safety factor or sorts can be provided by not fastening the vinyl tubing to the air stem or core depressor too securely so that if the depressor is not operated, the tubing will (hopefully...) blow off before the gauge is overpressurized.  A pressure relief valve would be even better.

Dispensing with a CO2 tire inflator without a pressure gauge is pretty easy with a bit of practice.  What I do is add the CO2 only as I'm actually dispensing brew- i.e. when brew flows too slowly, give it a brief blast of CO2.   You'll know when you've over-pressureized by the brew foaming too much as it's being dispensed.

Air from a bicycle pump works well but you'll need to consumme the brew in a day or less- otherwise it'll get oxidized and taste really bad.

If you want a tap cap that allows the use of both an access valve and a tire air stem, use a 1/8" NPT  tee and  close nipple instead of the street elbow.  You'll have to either chase the threads (i.e. a threading die turned "backwards") on the exposed part of the close nipple or use multiple  washers to take up slack between the nut/washer and the cap.

Photo	Description	Model No, '02 Price & Source
	Reusable 6-liter (1.5gallon) blue bottle. The bottles are 14" from end to end, and 6.25" in diameter with a 38mm top (a standard 3-liter bottle fits it).	KEG930  $6.95 (from Beer Beer & More Beer)
	CO2 Injector Only.   Does not include ball lock or adaptor hardware. Use to flush kegs or carboys prior to transfer or to flush the headspace in wine fermenters. Uses 12g cartridges	KEG954  $9.95 from Beer Beer & More Beer)
(no picture)	12 gram CO2 cartridges- pack of 12	KEG955A $7.80 from Beer Beer & More Beer)

6 Liter Minikeg Cooler

The Rubbermaid cooler above is too small to containg a 6 liter minikeg so I made one using a small plastic garbage pail inside a 5 gallon plastic pail.  It keeps homebrew well chilled when at room temperature for a day with a quart or two of ice.  To reduce the height of the assembled minikeg, I soldered some 1/4" copper elbows together to made a "U" atop the tap.

>I have made 3 different versions of your minikeg, but I have a big problem with foam. Whatever I try - I get ONLY foam.

Don't give up- the rig has worked for many folks.  If you are just starting out with kegging, it seems that everyone (me included) has a foaming problem.

>What's the secret? Can you help?

The basic secret is to have a sufficent and gradual pressure drop between the brew in the keg and that tap so there is not much pressure at the tap- just a psig or two at the tap is enough.  A related secret is to have the dispensing pressure the same as the carbonation pressure, assuming the temperatures are the same.   The following tips are all based on this basic secret.

The first time folks (me included!) dispense from kegs, they only open partially open the tap.  This always causes foaming.  Too much dispensing pressure encourages this- the brew will flow from the tap will flow too fast and foam so the dispenser will throttle back on the tap.  This does slow the flow but results in even more foaming at the tap due to the excessive pressure drop from the partially open tap.

If the tap line is too short, the pressure at the tap will be too high and the brew will foam due to the sudden change in pressure at the tap.  The same goes for a tap line with too large of a diameter.

Too much dispensing pressure will cause foaming.  There are two ways to aid in getting the dispensing pressure correct- install a pressure gauge downstream of the inflator so you can better assess and thereby control the pressure or pressurize while you are dispensing.  The gauge is the better approach IMHO.  The basic technique is too start with a  dispensing pressure which is too low (i.e. very little or no flow), gradually increase the pressure until too much foaming starts then stop pressurizing.  Be aware that it takes very little additional co2 or air to overpressurize a minikeg that is nearly full.  With a co2 tire inflator used for dispensing, a burst of co2 that's a mere fraction of a second too long will cause foaming with a full nearly keg.  Control of pressure is easier (and cheaper) with a simple bicycle air pump.  The downside is that you have to consume all of the brew in the keg in a day or it will become oxidized from the air.

If the minikeg warms during dispensing, there will be more foaming since the co2 will want to come out of solution.  I had this happen when I used a just an insulated jacket over a 3 liter bottle minikeg to keep it cool.  The jacket I used kept the brew cool enough for 3-4 hours- longer than that and it warmed too much and foamed when dispensed.  I now keep the brew in a cooler with ice during dispensing.  In a similar way, if the tubing to the tap is at a warm enough temperature, it will cause the brew to foam.  Keep the tubing cold by stuffing it down inside the cooler with the minikeg.

Over-carbonated brew can cause foaming.  The ideal is for the dispensing pressure to be just a bit above the carbonation pressure- just enough more pressure so you get a slow flow out of the tap.  When I started force carbonating in kegs by shaking the keg while adding co2, I tried to speed the process by using more pressure than called for and attempting to stop pressurizing before the bubbling of CO2 into the brew ceased.  This ALWAYS resulted in foamy brew.  Now I pressurize only to the target (and dispensing!) pressure while shaking the keg.  Getting the brew to the planned dispensing temperature before carbonating helps but you can use a co2 pressure/carbonation/temperature table to account for differnces in force carbonating and dispensing temperatures.

If you force-carbonate still brew in the minikeg by shaking it while pressurizing with CO2, let it settle down for at least a day before trying to dispense- otherwise, you will defintely dispense alot of foam.  I've never naturally carbonated brew in kegs so I can't offer advice for that.

Changes in flow direction or changes in diameter in the flow path (especially, and nonintutively, going from a smaller to larger diameter) will cause a pressure drop and hence tend to cause foaming.  A trapped vapor/gas pocket/bubble in the beer flow path reduces the effective diameter of the flow plumbing and can cause foaming.  As a data point, I just fitted a minikeg tap with a inverted "U" soldered together with two 1/4" copper elbows and tubing to reduce the overall height of the rig so it'd fit into a new cooler I cobbled together.  I was really concerned about the changes in diameter, flow direction and the obvious (and opaque) trap caused by the inverted U causing foaming during both counterpressure filling and dispensing but I noticed no difference compared with the previous arrangement which was just the brass beer tube going straight through the top of the brass elbow fitting atop the cap.  But I did change the filling process to ensure there was no trapped air or co2.  After sanitizing the bottle, I filled it completely with water and rapidly (to flush air out of the beer line and the trapped inverted U) by connecting the cobra tap to a water faucet using 3/8" ID vinyl tubing fitted over the snout of the tap and leaving the bottle cap loose.  I then tighten the cap and forced out *most* of the water out via the cobra tap by pressurizing the rig with CO2.  I left about 1/8" of water over the dip tube at the bottom of the bottle.  This ensured there was no air in the bottle (which could oxidize the brew) and ensured the beer line was full of water and hence had no trapped pockets of air or co2 which would cause foaming.  I then connected the cornie and the minikeg cobra taps together with a short lenght of 3/8" ID vinyl tubing fitted over their snouts and locked both taps open to start filling.  I can't say it helped since there was no more foaming than normal (1/16 to 1/8") while filling but, it did make me feel better.

As you can probably see, the above factors are interrelated- changing one factor usually requires fiddling with another one to ensure a good glass of brew.

Finally, as a data point, with both cornie and pop bottle minikegs at 10-12 psig and 32-45 degF (that's both the force carbonation and dispensing pressures and temperatures!), I use 6' to 8' of 3/16" ID vinyl tubing.  It takes me about four seconds to dispense 10 oz. of brew and wind up with an inch or so of foam in the glass.  Four seconds seems fast but it feels like forever when one is actually dispensing.  A higher dispensing pressure or serving temperature will require a longer length of tubing- ditto for larger diameter tubing.

Minimizing foam when dispensing- some tips in answer to an email I got.
John Schnupp's TapCap. (or at his page)

My old 3 liter mini-keg which uses a metal tire air stem.  It's more difficult to make than the one on this page and I've not found an air chuck to attach to the air stem that either didn't leak if left connected or wasted too much co2 when it was connected or disconnected.  I recommend the one on this page instead.