How do bar pumps and kegs work?

venquessa · 02-08-2012, 08:57 PM

I'm throwing this out there for discussion as something I don't really understand.

All I know is beer comes to the pub in an aluminum keg. There is CO2 cylinders involved.

So, from standing at the bar on a Saturday night watch the guy pour a pint... I'm thinking...

The keg comes flat, CO2 is used to pressurize the system with the tap on one end and the keg on the other. CO2 is used to force the beer out of the keg and to the pump. I'm suspecting that CO2 is also injected directly either before or at the tap.

The thing that puzzle me in the two position tap... pulled towards them seems to be "normal pour" with plently of gas, but momentarily push away from the pourer it pumps lots more gas.

Here a pint is pulled with the glass tilted so that no head forms until the last few inches when the glass is righted and the volume is topped up. This generally, with lagers results in head forming, if it doesn't or is not enough, the barman pushes the tap away from him which seems to inject much more gas for head. If he gets too much head, he pours it off and re-tops up.

**TomSD** · 02-08-2012, 09:03 PM

The keg comes already carbonated and under pressure. CO2 is hooked up to both maintain the carbonation and to push the beer through the lines for serving. The CO2 isn't injected into the beer at any point in the process as it is already in solution from the keg.

As for pouring... pouring down the side of the glass is done to minimize the CO2 coming out of solution by pouring it gently. Head is formed when CO2 comes out of solution (the beer) and rises to the surface. At the end of the pour straightening the mug and pouring the last bit right into the beer causes more CO2 to come out of solution forming the head. If you just poured it straight you would get a lot of head and very little beer when the mug was filled up.

Fiddling with the tap will depend on the type of tap but it is the same principle. Partially opening the tap, or with some taps there is actually a position for it, causes more CO2 to release from solution giving you more foam.

RDWHAHB · 02-08-2012, 09:08 PM

Quote:

Originally Posted by venquessa

All I know is beer comes to the pub in an aluminum keg.

You might not know that either....

Most all keg are stainless steel.

**weirdboy** · 02-08-2012, 09:13 PM

I note that the original poster is from the UK, where if one is speaking of "real ale" the beer is carbonated in the keg/cask, but then (typically) gradually loses carbonation over time as it is poured, because there isn't a cylinder on the other end pushing it and filling the empty space with pressurized CO2. Instead the space is filled with either air, or CO2 at essentially atmospheric pressure.

The method for getting the beer from the keg/cask to the faucet can involve either gravity, or a pump, hand pumps being common. There is sometimes a "sparkler" attached to the faucet which aerates the beer a bit while it is coming out so as to create a bit of foam.

**TomSD** · 02-08-2012, 09:14 PM

Since they mentioned kegs and CO2 I assumed they weren't talking about a beer engine. I've been wrong before though, lol.

**scottland** · 02-08-2012, 11:26 PM

The faucet you're thinking of is a 'creamer' faucet. It's used to pour beers that are served on 'beer gas' which is a mixture of co2 and nitrogen. If Guiness is an example of what you're thinking of, then we're on the same page. When they pull the faucet towards them it pours beer, then at the end, they push the faucet the other direction it forces the beer through the 'creamer' which causes the beer to foam, and leaves a nice head.

Teromous · 02-09-2012, 12:00 AM

All you ever wanted to know and more, from Perlick

venquessa · 02-09-2012, 07:51 AM

Quote:

Originally Posted by Teromous

All you ever wanted to know and more, from Perlick

This looks very much like it. But it's not just Guinness that's poured that way here (besides Guinness has a special way of being poured that a lot of "foreigners" don't get and usually makes you frown when you get a pint of Guinness in a naive English pub). I had a friend hand a pint of guinness back and ask for it to be poured properly, because it arrived at the table in under 1 minute. Guinness (and some other beers) also comes in Guinness Extra Cold form in pubs here, where it is pumped/piped through a refrigeration unit on the way to the tap.

Lager is also poured this way. In a pub here if someone hands you a pint of beer with any more than 5mm (1/4") head you might ask for it to topped up, you paid for a pint of beer, not 90% beer 10% foam. Guinness is the exception, where the head should be about 10mm-15mm or 1/2".

I'm in Northern Ireland, which is both UK and Ireland. So, Guinness is one of the breweries supplying a lot of pubs. In Dublin they have a saying that bus lanes are only allowed to be used by Buses, Taxi's and the Guinness lorry.

**firstRWD** · 02-09-2012, 08:22 AM

I wish I could add to this and answer your question, but I just wanted to say I LOVED the beer when I went to Ireland and the UK and you're incredibly lucky. Most any place you went here would make you a little sad(just the beer in general compared to there) and the head would make you give a beer back every time, which would probably result in a bar tender being somewhat rude to you for their lack of caring/ability and you expecting a decent head. I pretty much always expect at least 1" (15cm) of head on a normal beer and closer to 25cm on a nitro(Guinness) when I go to a normal bar/brewpub in the US. From what I learned at the Guinness brewery while I was in Dublin, it's that the beer there is lightly CO2/Nitro'd when they pull the tap handle toward them, and a good bit more CO2/nitro when they push it away, basically as someone else said above. Here in the US it's just standard pull toward them (I don't think they even have taps that push away with different gas) and you get lots of head or more carbonated beer depending on the beer/pour. Like I said, you're lucky your taps are even designed that way, that your bar tenders actually care, and you guys have way better beer in general. Next time I visit I'm planning an extra 100euro/lbs just for beer.

Edd · 02-09-2012, 09:28 AM

Quote:

Originally Posted by venquessa

This looks very much like it. But it's not just Guinness that's poured that way here (besides Guinness has a special way of being poured that a lot of "foreigners" don't get and usually makes you frown when you get a pint of Guinness in a naive English pub). I had a friend hand a pint of guinness back and ask for it to be poured properly, because it arrived at the table in under 1 minute. Guinness (and some other beers) also comes in Guinness Extra Cold form in pubs here, where it is pumped/piped through a refrigeration unit on the way to the tap.

Lager is also poured this way. In a pub here if someone hands you a pint of beer with any more than 5mm (1/4") head you might ask for it to topped up, you paid for a pint of beer, not 90% beer 10% foam. Guinness is the exception, where the head should be about 10mm-15mm or 1/2".

A couple of points on this - firstly almost all keg beers you will find on a bar will pass through a refrigeration unit at some point. Cellar temperature in the UK is usually between 10 and 14C, keeping at the preferred temperature for lagers would keep it far too cold for ales and there is of course the expense factor, keeping a cellar at 5C or below would be prohibitively expensive.

Secondly when you get a pint over here you can ask for a top up if more than 5% of the beer is head. A small but vital detail when you consider the disparities in glass style you can get!