Draft beer extraction pressure: mystery solved

The Importance of Draft Beer Extraction Pressure

There is nothing better than tasting your favorite beer, or discovering a new one, and feeling the harmony between flavor and carbonation, right? But that harmony takes care. To maintain beer quality and avoid losses, attention is essential at the moment of draft beer extraction.

Carbonation and Pressure: What You Need to Know

Every beer contains dissolved carbon dioxide (CO2). Manufacturers control the volume of CO2 according to the beer style, in a process known as carbonation. Each style, therefore, has an ideal pressure in the keg. To draw the draft beer, we apply an extraction pressure, which must be compatible with that ideal pressure. That is why it is essential to use individual pressure regulators (manifolds), allowing proper control of the gas pressure on each keg.

Delivering the Perfect Beer to the Glass

The goal is to deliver the beer to the customer with the same CO2 level it had in the keg. When that happens, the draft beer comes out clear, with ideal foam and no waste. And this depends exclusively on the extraction pressure applied. Many establishments fail at this point, hurting the customer experience and piling up losses. If the beer ends up over- or under-carbonated, the customer is unlikely to return. In extreme cases, the keg has to be discarded, wasting both draft beer and gas.

Resistance in the Draft Beer Line

Even with the correct carbonation pressure, the draft beer line offers resistance. For the beer to reach the glass, you need to apply an extraction pressure higher than the carbonation pressure. This happens because of factors such as:

• Hose length and diameter
• Keg height relative to the tap
• Number of pieces of equipment in the line (draft beer dispenser, buffer tank, pre-chiller, sensors, valves, etc.)

Two Common Problems

When dealing with extraction pressure, you may run into two scenarios:

1. Insufficient pressure:
The CO2 pressure is correct to maintain carbonation, but it does not overcome the line’s resistance. The beer does not arrive with the necessary force and foams as it comes out.

2. Excessive pressure:
The pressure overcomes the resistance but exceeds the ideal carbonation level. The beer keeps absorbing CO2 and also foams at the outlet.

How do you know the correct draft beer extraction pressure?

• 1. Check the beer’s current pressure in the keg

As we saw, each beer style will have a different carbonation and, therefore, a different pressure in the keg. So first we need to know the beer’s current pressure in the keg.

This pressure is calculated according to the CO2 level you want to achieve (which depends on the style) and also the temperature the beer is at. The lower the temperature, the more gas is incorporated into the beer and the less pressure is needed to reach the ideal CO2 level. Below is an example of the average pressure for most beers (American ales and lagers, 2.2 to 2.7 volumes of CO2) according to temperature and for two different types of operation:

From the table, you can see that the keg’s operating temperature has a major influence on the extraction pressure, which is why we will separate the tips to help you get the extraction right in the two setups.

• 2. Check whether it is possible to use nitrogen mixed with CO2 for draft beer extraction

Another important piece of information is the possibility of using nitrogen mixed with CO2 for extraction. This mix can be bought ready-made (already in a cylinder and with the percentage you want), or you can use a gas blender, which takes one CO2 input and one N2 input and lets you control the proportion of each gas at the output. By mixing the gases, the proportional amount of CO2 in the volume decreases, making it possible to work with a higher extraction pressure while keeping a smaller share of CO2 and making it easier to keep the CO2 balanced between the carbonation pressure and the extraction pressure. We will give examples of different mixes for each type of operation. To get the CO2 pressure of the mix, just multiply the pressure applied to the mix by the CO2 percentage.

Draft beer extraction with a refrigerated keg

Operating with a refrigerated draft beer keg is highly recommended for places with lower keg sales, either because of low foot traffic or because of a wider variety of styles. The refrigerated keg preserves the beer for longer and you avoid losses in your establishment. In this setup you need to keep the kegs refrigerated at all times, at the ideal serving temperature. Usually a cold room and a refrigerated counter are the main equipment used for this. Keep in mind that a keg can take up to 24 hours to stabilize at the cold room temperature, so always keep a chilled stock available. 

As the carbonation table above shows, a cold keg absorbs more CO2 than a warmer keg, and it is also more sensitive to temperature variation (just a few degrees cause a significant change in carbonation pressure). Because of that, you need to be a little more careful with the adjustments so you do not change the beer’s carbonation. In this setup, the draft beer line is usually short and does not have many pieces of equipment, but there are longer lines that use a python, pre-chillers, and buffer tanks. The longer the line and the more equipment it has, the more pressure will be needed to get a good extraction, but at this temperature the only way to achieve that is by using a mix of N2 and CO2. 

Below is a table with examples of average extraction pressure that can be used as a reference for beer at 4ºC. 

Note that this guide is a starting point to help you begin the process of finding the ideal draft beer extraction pressure under your bar’s conditions, okay?

A 50% N2 and CO2 mix is our suggestion for operating with a cold room or refrigerated counter with a short line. Adding N2 lets you work with a slightly wider pressure range and avoid losses.
** Lines that keep the kegs refrigerated but serve remotely, not directly in the cold room, using a python, draft beer dispenser, pre-chiller, etc., need to use a higher pressure (2.5 to 2.7 kgf/cm²), so the recommended mix is 25% CO2 and 75% N2

Operating with a keg at room temperature

Operating with a keg at room temperature, with equipment to chill the beer at the moment of service (draft beer dispenser, pre-chiller, etc.), is recommended in places where beer sales are high. A room-temperature keg has a very short shelf life once opened, just a few days, and needs to be sold quickly to maintain its quality. This type of system takes up less space, the stock can be kept at room temperature, and you do not need to wait the 24 hours for the keg to reach serving temperature inside a cold room. It is very practical and works very well in bars with few styles (usually just a pilsner and one more complementary style) and good beer sales.

As for extraction pressure, a rise in the beer’s temperature means it needs more pressure to maintain its ideal carbonation. In the room temperature range (24ºC to 30ºC), the draft beer needs approximately 2.5 kgf/cm² of CO2, as shown in the table above. In this case, the very pressure used to maintain the beer’s carbonation is already enough to draw it through the required equipment, without having to add more pressure or an N2 mix.

Finding the ideal extraction pressure for the beer style you are serving and for your specific line will take a bit of care at first. Once you find a good way of working, the result will be a beer with the right carbonation, perfect foam, a happier customer, and you cutting draft beer waste to the minimum.

Mystery solved!

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