Article

The Nitrogen Effect

It’s common for Americans, particularly those Americans who may not fully appreciate the diversity of all the world’s beer styles, to say that the English “like to drink their beer warm and flat.” On the other hand many a Brit when confronted with standard American commercial beer has been heard to mutter some comment about “freezing seltzer water.” Both statements are overcritical and somewhat exaggerated, but both have a basis in fact.

Mainstream American commercial beers are brewed to be very light. That is, they are very short on the critical ingredients, malt and hops, that produce most of the flavor in beer. This lightness is not a defect; it is in fact the distinctive characteristic of this beer style, and there is good reason for it. These beers are crafted to be light and refreshing and, as the commercial says, “less filling.”

Because of the composition of these American beers, they are meant to be consumed very cold (below 42° F) and with a high level of carbonation. The CO2 bubbles enhance the refreshing characteristic, and a hefty level of carbonation particularly brings out what hop bitterness and flavor there is. As we all know, mainstream American commercial beers are not very pleasant if they are allowed to go “warm and flat.”

English ales, served as they should be, are the opposite. These beer styles were developed long before the invention of refrigeration and forced carbonation, so they are brewed for the conditions of that time. Traditional stouts, porters, milds, bitters, and other ales have a lot of flavor from both malt and hops. They are made to be cask-conditioned, originally in wooden barrels. Wooden casks obviously wouldn’t hold much CO2 pressure, so these beers are crafted to be very low in carbonation. They are served at cellar temperatures, about 55° F.

Far from being just “warm and flat,” traditional English ales are rich and creamy. The higher temperature and lower carbonation showcase the full flavor of the malts. Homebrewers can replicate the taste and feel of these traditional styles.

Introducing Nitrogen
Traditionally, cask-conditioned English ales were served with a hand pump, or “beer engine.” The barrels in the cellar of the pub were connected to the tap faucets on the bar upstairs, and the beer was drawn up by pumping air into the barrel. These hand pumps delivered about 25 to 30 pounds per square inch (psi) — and at one time you could tell an English barmaid by her well-developed arm and shoulder muscles!

Air is 78 percent nitrogen, so they were pumping beer that had a low level of carbonation with something that was mostly nitrogen.

The trouble with using air to pump beer is that the remaining 21 percent of air is mostly oxygen. If a keg is going to be consumed quickly, using air is okay. But if the beer is consumed over a period of more than one day, it quickly becomes oxidized. To avoid oxidation but duplicate the effects of traditional cask ale, modern pubs pump their low-carbonation draft ales with a mixture of 75 percent nitrogen and 25 percent carbon dioxide at high pressure, about 28 to 30 psi. Homebrewers can do this too, but using nitrogen is not as easy as CO2.

It’s important to understand some basics. Nitrogen doesn’t behave like CO2. Nitrogen doesn’t have the affinity for going into solution like carbon dioxide does. Professional breweries “nitrogenate” their beer by chilling the beer to 32° F and forcing nitrogen into it under extremetly high pressure. Nitrogenation helps brewers re-create the smooth feel and thick head of cask ales. If you tried brewing a batch of homebrew, moving it into a keg, then pressurizing with nitrogen for a number of days, the only result would be a tap delivering very flat, high-pressure homebrew. As a safety note, most homebrew equipment is not designed to handle the pressure needed to force nitrogen into beer.

In the pubs nitrogen is also used as a pusher to deliver the beer to the taps. The benefit of nitrogen-tapped beers that homebrewers want to emulate are those delicious, tiny, creamy bubbles. And yes, you can do that.

The Nitrogen Effect
A good example of the nitrogen-as-a-pusher idea is those great Draught Guinness cans, also used now to package and distribute Murphy’s Irish Stout, Boddington’s Ale, and others. In the bottom of those cans is a hollow plastic disk pierced with a tiny laser-cut pinhole.

The 16.9-ounce cans are filled with 14.9 ounces of beer and a minute amount of liquid nitrogen. Then the can lid is quickly attached. As the liquid nitrogen warms, it turns to gas, raising the pressure inside the can and forcing about 1 percent of the beer into the hollow plastic disk. When the can is opened, the pressure is released. That small amount of beer streams out through the tiny hole, creating a geyser effect inside the can. This agitation causes carbon dioxide to be physically knocked out of solution, creating the little creamy bubbles. It’s just like a draft beer in a traditional English pub — high pressure, low carbonation.

It’s actually more difficult for pubs and bars to achieve an authentic cask-conditioned effect in dispensing their beers than it is for homebrewers. In a pub, especially in a brewpub, the beer often has to be moved a great distance under pressure to get it to the taps. It’s quite common for the brewhouse to be in another room or in a cellar, and sometimes it’s even in another building.

Kegged beer has to be kept under serving pressure in the delivery line 24 hours a day until the keg is empty, and since the line may be quite long, the pressure has to be high. Obviously, if CO2 pressure were used for this (as it is for American beer styles), the effect would be to put a high level of carbonation into the beer. This is not wanted in traditional English cask ales, and it is rather difficult for the pub to avoid doing it.

The most simple solution for a brewpub is to pressurize these beers with “G-mix” gas, a mixture of 75 percent nitrogen and 25 percent carbon dioxide.

Some of the larger brewpubs mix their own gas, but this is a very technical and expensive method. By doing so, they can use bottles of pure nitrogen and pure CO2 in combination, running the hoses through a “blender box” that precisely controls the mix.

Nitrogen for Homebrewers

After overcoming some minor technical problems and some expense, any homebrewer can follow brewpubs and pressurize his kegged beer with G-mix gas. Instead of using CO2, hook up the G-mix and apply it at about 25 psi. The nitrogen supplies the push while the CO2 maintains the low carbonation of the beer.

G-mix gas is not always easy to find. If you live in a rural area or small city, you may be out of luck for nitrogen experiments.

There are some minor technical problems and some expense involved any time bottled nitrogen gas or “G-mix” is used. For one thing, sellers of compressed gases won’t put nitrogen in a CO2 bottle. CO2 bottles are only rated at 1,800 psi, though they are tested at about 3,000 psi. When a small CO2 bottle of the kind usually used by homebrewers is filled, it is filled by weight. The CO2 inside the bottle is actually a liquid, and a five-pound bottle is filled with five pounds of liquid CO2, which delivers a pressure of about 900 psi.

Five pounds of liquid CO2 goes a long way, because the liquid inside the tank keeps generating more CO2 gas as the pressure drops. When the pressure gauge says the tank is half full, about 450 psi, the tank is almost empty because all the liquid has been changed into compressed gas at that point.

Nitrogen is just a compressed gas. It won’t liquefy at normal pressures and temperatures, so the only way to put a supply into a tank is to compress it as a gas and just pump as much as possible in there. Nitrogen (or G-mix) tanks have to be much larger than CO2 tanks to hold any usable amount of gas, and they have to be much thicker. Nitrogen and G-mix tanks are usually filled to 2,250 psi, so the construction and expense of the tank is much greater than that of a CO2 bottle.

Because it remains a gas in the tank, a large bottle of nitrogen or G-mix holds much less than a smaller bottle of CO2. Since the pressure is so much higher, a different pressure gauge is usually required as well. CO2 gauges often won’t go high enough for nitrogen. And in any case, an adapter is required to fit a CO2 gauge to a nitrogen bottle, because the neck sizes and threads are different.

An Authentic Alternative
Fortunately, homebrewers don’t have many of the problems that pubs and brewpubs do in dispensing authentic cask-conditioned English ales. Because you are dealing with smaller volumes, have shorter delivery lines, and don’t have to maintain a constant serving
pressure, you can re-create the nitrogen-pushed authentic English ale effect easily and cheaply, without nitrogen.

First, make sure the beer recipes you want to dispense will be good at 55° F with low carbonation. Some beers are great when served in this way and others are not. Many brewpubs and microbreweries have been disappointed to find that some of their best beers became one-dimensional and bland when served with low carbonation. The best candidates for this treatment are traditional stouts, porters, milds, and bitters.

Good hop flavor and aroma and the flavors from specialty grains are important in beers with low carbonation. If you have some of your favorite beer bottled, open one and let it sit for a couple of hours before drinking it. If it seems better that way, that recipe is a good candidate for a traditional English draft beer.

To be prepared for traditional serving, a beer must have a low level of carbonation. If you are adding priming sugar when kegging, cut the amount to one-third cup of corn sugar in five gallons of beer. If you are artificially carbonating, put the keg in the refrigerator, apply 20 psi CO2 pressure and give it a shake. The next day, take the keg out of the refrigerator, let it warm up to 55° F, and draw off some beer to check; there should be some carbonation, but not much. Stir the beer with a spoon and see if some CO2 bubbles are knocked out of solution.

When you feel that the beer has the proper low level of carbonation, keep it at 55° F and reduce the CO2 pressure to 5 psi to maintain it. A stick-on strip thermometer on the keg is very helpful for checking the liquid temperature.

To get the proper head you need a restrictor on your tap. Restrictor tap faucets can be ordered specially for you by your homebrew supplier, but they cost more than $100. The Guinness tap system in pubs uses a disk about the size of a penny that is inserted into the tap faucet. The disk has five tiny holes drilled in it. High-pressure nitrogen forces the beer through those five holes, creating the “creamy” effect by knocking the low-pressure CO2 out of solution and creating those tiny bubbles.

Try drilling five holes in a food-grade pastic disk the size of a penny. The disk should just fit the inside diameter of your tap faucet. Here’s the place to do a little experimenting and to be inventive.

Then comes the time to serve the beer, and nothing could be easier. With the keg at 55° F, increase CO2 pressure to 25 psi, but keep it there only while you are drawing the beer! Pressure this high would increase the level of carbonation in the beer in time, but in short spurts it won’t hurt anything. Carbon dioxide at 25 psi will push the beer through the restrictor and knock tiny bubbles of CO2 out of solution, producing the desired creamy effect. Immediately after tapping a beer, turn the pressure back down to 5 psi.

That’s all there is to it. With a little practice, you can even achieve that “cascade” effect when drawing a pint of your favorite traditional English ale.