Kegs themselves are considered either open system or closed system:
- Kegs with a bunghole on the side that allows the interior to be readily accessed for inspection and cleaning (ie: Hoff-Stevens and Golden Gate kegs) are examples of an open system keg.
- American Sankey-style kegs, which require specialized automated equipment for cleaning and filling, represent the closed system design.
Open-system kegs can be accessed without extracting the valve body or spear by way of a bunghole in the side of the keg that is closed by a wooden or plastic bung plug. The openings allow the kegs to be visually inspected before filling and for the kegs to be cleaned manually.
Hoff-Stevens systems are the second most common type of keg, are sometimes called a “two-probe” keg. The Hoff-Stevens keg has a centered valve protruding from the top in addition to the bunghole in the side. Due to their tipsy shape and lack of chime they are frequently stored and shipped on their side, though they must be in the upright position when tapped for dispensing. Hoff-Stevens kegs are larger in circumference than the American Sankey kegs and are without handles, making them more difficult to move and stack than Sankey kegs.
The valve in the top center of the keg is threaded on the outside. In the center of the valve is a hole, which is blocked by a spring-loaded ball. This part of the valve is connected to the bottom of the keg by a plastic internal pick-up tube. To the side of the center hole is a slightly smaller hole, which is also blocked by a spring-loaded ball. When the Hoff-Stevens tap is inserted, and the wing-nut collar tightened down, the two tubes of the tap open the check balls of the valve and allow CO2 to flow through the small probe into the headspace of the keg. Beer is then pushed up the center tube to the tap. Unlike the Sankey keg fitting, the Hoff-Stevens tavern head does not control the CO2 at the valve, so you must cut the flow of CO2 at the regulator when changing kegs.
Hoff-Stevens kegs require more attention than Sankey kegs. One drawback is the plastic pick-up tube can be damaged or separated from the valve during racking. It’s rare but if this happens the keg cannot be repaired without first being emptied, then pulling the valve. Fortunately this can be accomplished with a removal tool or standard tools, but you lose a half barrel of good beer. Another potential problem involves the small “figure-8″ gasket that seals two-probe valve. If the gasket is damaged or lost, both beer and CO2 will leak from the keg when tapped; often with considerable force.
For those reasons, many people choose to purchase Hoff-Stevens kegs that have been retrofitted for the Sankey-style valve system. Hoff-Stevens kegs do have some positive aspects. The bunghole allows them to be cleaned, inspected, and filled without automated equipment, and kegs with bungs are decidedly less expensive than kegs without bungs, both in terms of cooperage price and cleaning/filling equipment.
Golden Gate Systems – The Golden Gate keg is very similar in shape to the Hoff-Stevens; it is barrel-shaped, has no chime or handles, and has a bunghole. The difference is in the tapping device. A Golden Gate keg has two valve housings instead of one: one at the top center of the keg for adding CO2, and the other near the bottom on the side for drawing beer out. These kegs are difficult to empty completely; the keg must either be tilted or a “snorkel” device used to reach the last bit of beer. Thus, two-valve kegs usually leave from 6 to 23 oz in the keg, whereas single-valve kegs rarely leave more than 2-3 oz of beer. Furthermore, the beer outlet is difficult to reach and frequently leaks when the rubber washer is not seating well or is getting worn.
Golden Gate kegs are very difficult to find today. In a market almost completely dominated by single-hole kegs, it is quite possible that distributors or draught accounts will reject Golden Gate kegs. Most Golden Gate kegs have been converted to single-hole kegs by welding closed the bottom valve and bunghole and installing a Sankey or Hoff-Stevens fitting on the top. The few intact Golden Gate kegs still in use are best used to serve cask-conditioned beers, because they can pour by gravity through the bottom valve while venting through the top valve. Open system kegs all suffer the same downside of leaking bungs and gaskets, offsetting those sweet initial savings with off-condition beer, returned kegs, shorter shelf life, and loss of customer confidence.
Closed-system kegs are upright, cylindrical vessels, usually straight-sided. Available in stainless steel, stainless steel cylinder covered with polyurethane (designed to reduce noise), and FDA approved molded polypropylene plastic. Older kegs may have an aluminum cylinder. Closed system kegs have a rim, called a chime, on each end. The top chime has integrated handles for easy handling and can have the brewery’s name embossed on the side. The top of the vessel is a concentric valve fitting (aka coupler) in the center allowing for easy dispensing, cleaning, and filling.
Introduced in the 1960s from the UK, the advent of Sankey-style kegs offered huge labor savings for the beer industry compared to the old bung-style kegs previously in use. Brewers and Draught accounts preferred the closed-system keg over the open-system keg for several important reasons, ease of tapping, ease of storage and handling, and the improved profit margin due to the reduction of beer loss commonly associated with the open system keg design.
Unlike open-system kegs, closed-system kegs can be accessed only through the valve housing. All cleaning and filling is accomplished without extracting the valve. The interior shape of a closed-system keg is designed for efficient cleaning by means of automated equipment that opens both valve ports, injects cleaning agents, rinses, and sanitizes while the keg is inverted with the valve down. The keg can be filled inverted or upright. Closed-system kegs are less vulnerable to infection than open-system kegs because they restrict the access of air to the interior more than bung-style kegs do. The downside is that closed-system kegs require automated cleaning, which involves an initial investment in equipment.
Half-barrel keg - The half-barrel keg, or half keg, is the standard keg available in the United States. It measures 23 inches tall and has a diameter of 16 to 17 inches. It can hold 15.5 gallons and weighs 160.5 lbs. when filled to capacity. Quarter-Barrel Keg – A quarter-barrel keg is the second most common keg type available in the United States. It has a capacity of 7.75 gallons, and is commonly referred to as a pony keg.
Sixth barrel keg - The sixth barrel keg is the smallest option available. Sixth barrels technically hold 5.1 gallons of beer, but some kegs that hold 5.5 gallons are sold as sixth-barrel kegs. Sixth barrel kegs are commonly referred to as torpedo kegs because of their long, cylindrical shape. Import Keg – The import keg, is the common keg type used in European countries. It has a 13.2-gallon capacity, making it the size between a half-barrel keg and quarter-barrel keg.
Cornelius keg - also known as a Corny keg, has a five-gallon capacity. Corny kegs were originally used by the soft drink industry for storing the soft drink mix for fountain drinks.
Mini keg - A mini keg has a storage capacity of only 1.32 gallons of beer. These kegs are made of aluminum and can be recycled after use. Unlike other keg types that you would rent from a distributor, mini kegs can be purchased from most alcohol retailers. They are popular for their compact size that easily fits on your refrigerator shelf. This keg type might also be called a bubba keg DIN-keg and Euro-keg
In European countries the most common keg size is 50 liters – this includes the UK with its non-metric keg system where the standard keg of 11 imperial gallons is almost exactly the size of 50 liters in the metric system. The German DIN 6647-1 and DIN 6647-2 have also defined Kegs in the sizes of 30 and 20 liters. A newer Euro regulation defines 50, 30, 25 and 20 liters where the Keg shape is usually thicker but less tall than the German keg specifications.
- D Coupler (aka “Sankey”): Standard coupler, for most types of American kegs-domestic & micros, as well as the Canadian, Mexican, and many Asian imports
- S Coupler (“Euro-Sankey”): Many UK and Euro imports (Newcastle, Heineken, Stella, Beck’s, Pilsner Urquell, etc)
- A Coupler (“German-Slider”): Most German imports (Paulaner, Spaten etc)
- M Coupler (the “other” German-Slider):
- A couple of German, like Schneider
- U Coupler (“Guiness”): Guinesss, Harp, a few others from Ireland/UK
- G Coupler (“Bass”); Bass, Anchor (SF), a few others
- Twin Probe (“Hoff-Stevens”): An older style slowly being phased out and used by few.
GoldenGate: Uses an attachment at the top for gas/air pump and another attachment on the side near the base of the keg for the faucet.
American Sankey-style valves. This valve arrangement consists of a stainless steel rod housing, called a combination fitting, that is permanently installed into the top center of the keg and sealed with a spring-loaded check ball. The tapping device, or tavern head, fits into the lug housing of the valve. When the tap is opened, a probe extends and opens the check ball of the combination fitting. Carbon dioxide enters the keg and forces beer up the rod into the beer line and on to the faucet. Virtually all large breweries, and most micros, are now using this combination. The fittings are easy to use with one hand and control both the beer flow and CO2 flow at the valve. Closed-system kegs must use Sankey-style valves. These types of kegs are the most expensive on the market, both in terms of cooperage cost and cleaning and racking costs. The fact that maintenance of Sankey kegs is minimal and the failure rate is far less than that seen from a two-valve keg offsets this initial investment, however. In fact, the only regular maintenance needed on a Sankey keg is replacing the gaskets in the combination fitting, and this only rarely needs doing. When it does, a specialty tool is required to get the valve out of the keg. With considerable effort the valve stem can be removed without this tool, but for safety reasons this method should not be used except in dire emergencies, and should not be attempted at all before pressure is vented from the keg. The tavern head gaskets themselves, however, are both inexpensive and easily replaced. Adding to the up-front cost is the price of the necessary automated cleaning equipment.