keg volume

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keg volume

Postby mccarty » Wed Sep 19, 2001 1:34 pm

I have read that you must leave some headspace in a keg. Can someone please answer the following question? What is the volume of a 5 gallon keg, 3 gallon keg and a 2.5 gallon keg. If I make a 5 gallon batch, do I have to be concerned with headspace if I use a 5 gallon keg? Will it be completely filled up? If you need to split up a 5 gallon batch for refrigerator purposes, would it be better to use two 3 gallon kegs or two 2.5 gallon kegs.

Thanks in advance.

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Joined: Wed Sep 19, 2001 5:32 pm

A 5 gallon keg is a 5 gallon keg...

Postby Mesa Maltworks » Wed Sep 19, 2001 4:25 pm

I assume the 5, 3 & 2.5 gallon "kegs" you are referring to are Cornelius (TM) cylinders. Depending on the country you live in, there are sanke and other comercially fitted kegs in those increments.

Assuming these cylinders are what you have, the net capacity is that embossed on the cylinder. These cylinders were designed to hold soda syrup that is thick and uncarbonated. They were filled to this capacity when released from the factory.

Beer, on the otherhand, is carbonated and in a home brewing situation is typically force carbonated in the cylinder as well. If you do not leave a headspace, you can damage the internal workings of the pressure relief valve for 2 reasons: 1) when you apply high pressure to carbonate the beer, the beer can rush into the relief diaphragm and 2) the inital burst of pressure can rupture the diapragm due to a lack of equalization space. (ie.. get ready for a beer shower !) Also, homebrewers typically shake the cylinder to disburse the CO2 into the beer quicker. If you don't leave a headspace, the foam has nowhere to go but up into the valve.

Another consideration (this has happened to me !) is if you aren't paying attention to the regulator setting on your gauge and the pressure in the cylinder is higher than the CO2 setting, when you connect the fitting and hose to the gas inlet you end up ruining your regulator by filling it with beer !

Heres a goodie... a friend of mine that was unaware that the cylinder side of the gauge had gone bad AND the cylinder was empty. He had not checked first to see if he could pressurize the gas line and guess what.... he shot a bunch of the beer into the CO2 cylinder due to the pressure differential between the two AND killed his regulator as well !!! This is what led him to purchase a stopcock with a check valve in it for the CO2 out line !!!! (I recommend to everyone do this).

While on the topic of gas in lines... most CO2 is not especially clean due to the production methods which can include recovery from corn based fermentation. This can lead to vegetal flavors being transferred into force carbonated beers. Another problem, if that one doesn't get you, is that vendors almost never clean CO2 cylinders ! You can just imagine what can happen to one of these in a bar setting with the example I illustrated that my friend experienced. Not only can they have beer sloshing in them, they also are an incredible source of contaminants from oils to bacteria.

The solution to this is to install a .02 micron in-line gas filter (about $ 8) between the cylinder out and the gas in of your cylinder. These filters last a long time and are worth the protection. I change mine about every 6 months, you wouldn't believe the crap they filter out !

A novel use I came up with for this same filter is to place it on a hose that allows oxygen from the air (and anything else for that matter) in casks while on beer engine dispense. This greatly extends the life of the beer that has been casked and does not violate any of the CAMRA edicts on proper real ale cask dispense.

Anyway... leave a headspace to avoid problems and to this end, if you split a batch, use 2-3 gallon cylinders, not 2-2.5s.

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