Dear Mr. Wizard,
I am an extract/specialty grain beer brewer. I keg 90 percent of my homebrew, brew in 5-gallon batches and use oxygen to aerate my wort. I make full-wort boils, use forced cooling and I also use liquid yeast. I am interested in using nitrogen to carbonate some of my brews. However, I have no information on how to do this. Do I use only nitrogen? Or do I use a mix of carbon dioxide and nitrogen? Do I use the same pressure charts that I used for carbon dioxide, or are there different charts? Does the gas come in a pre-mix (nitrogen and carbon dioxide) bottle? How does temperature affect nitrogen’s solubility in beer? Any help that you could give on this subject would be greatly appreciated.
Mr. Wizard replies:
The process of adding nitrogen to beer is referred to as nitrogenation. This is somewhat of a misnomer since nitrogenated beers also contain carbon dioxide and the gas blend used for the process is usually 75 percent nitrogen and 25 percent carbon dioxide. This mix is used to dispense draught Guinness Stout and is easy to find in markets that have draught Guinness.
Nitrogenated beers typically contain very low amounts of carbon dioxide, around 2.4 g/L or 1.2 volumes, and an even lower concentration of nitrogen of about 20 mg/L. “Typical” beers contain about 5 g/L of carbon dioxide and no nitrogen. The concentration of nitrogen is much lower than the carbon dioxide content because nitrogen is not very soluble in liquids. When dispensed through a special faucet, the nitrogen “breaks out” of the beer and forms very small, stable bubbles. Nitrogen foams are much more stable than carbon dioxide foams because the atmosphere is about 79 percent nitrogen and there is not much driving force between the gas concentration in the bubble and the concentration in the atmosphere. That’s why “nitro” beers have such awesome, stable foam. The density and creaminess of the foam also adds a terrific mouthfeel to the beer.
Unfortunately, there are not many good references on how to nitrogenate beer. This is probably because there is a trick to it and the companies with that knowledge are not anxious to educate their competition. Like many brewers, Mr. Wizard loves nitrogenated beers and has some rules of thumb on the procedure.
For starters, don’t bother nitrogenating any beer unless you have the proper faucet. There are many “stout” faucets on the market that are based on the Guinness faucet. All of these faucets have a disc with small holes inserted in the beer flow path and a device called a “flow straightener” placed after the disc. As beer flows through the holes in the disc there is a large reduction in pressure and this pressure drop causes the nitrogen and carbon dioxide to break out of solution. If the gas blend is just right you get a great glass of milky looking beer that settles out with a perfect head.
The other piece of equipment that is very important is a carbonation stone. I recommend the type of stone that can be connected to a stainless-steel rod and attached to the “out” fitting on a Cornelius soda keg. The stone is important because nitrogen is insoluble and it really helps to have small bubbles dispersed in the beer during the nitrogenation procedure. The key is getting the right gas blend. Too much carbon dioxide results in a large foamy head that doesn’t settle properly — and too much nitrogen results in “wild beer” that will foam uncontrollably. Too little dissolved gas produces a pint that just seems flat.
Steps Required for Proper Nitrogenation
Rack your beer to a keg after fermentation is complete (add finings if desired) and pressurize the headspace of the keg with mixed gas (75 percent nitrogen and 25 percent carbon dioxide) to a pressure of 10 to 15 psi. This pressure is used to seal the keg and does not serve to nitrogenate the beer. Do not pressurize with 100 percent carbon dioxide because the beer will absorb too much.
Transfer the keg to the coldest place you can find, preferably a refrigerator set at about 34° F, and allow the beer to clarify. I recommend about two weeks.
Step 2 (alternate)
Filter the beer after holding cold for about one week. I have found that nitro beers pour much better when they are free of yeast.
Make sure your beer is cold (between 34° and 38° F) and connect the mixed gas supply to the carbonating stone and set the pressure regulator to 30 psi. Gas will bubble though the beer until the headspace pressure reaches 30 psi. After the headspace pressure is at 30 psi, slowly loosen the pressure- relief fitting on the top of the keg until you hear a very low flow of gas escaping from the fitting. Allow the mixed gas to slowly bubble through the beer for 30 minutes. (If foam begins to come out of the fitting, tighten the fitting and allow the beer to rest for 30 minutes before continuing the slow bleed.) After this 30-minute purge, tighten the pressure-relief fitting and allow the beer to rest for 30 minutes, then do another 30-minute purge.
Hook up the mixed gas to the headspace of the keg and set the pressure regulator to 30 psi. Let the beer sit still for a few hours before pouring.
Pour yourself a pint of nitro homebrew! If the foam seems excessive you should use a lower pressure the next time around and if it seems a bit flat you can repeat Step 3, using a higher pressure.
Dear Mr. Wizard:
I quit brewing several months ago because I’m on a low-carbohydrate diet. I have lost about 35 pounds and I will probably continue to eat the same way for the rest of my life. The only commercial beer that fits into my diet is Miller Lite (about 3 grams of carbohydrates per 12-ounce can). Have you ever tasted that stuff? It’s less than flavorful! Do you know of a way to calculate carbohydrates in homebrew recipes? It seems like there should be a way to brew beer that is low in carbohydrates (3 to 5 grams per serving), but still make it taste good. But I would have to be able to calculate the carbohydrates (not calories, that doesn’t count). Is this a possibility and if so, do you have any low- carbohydrate beer recipes?
Mr. Wizard replies:
You can approximate the carbohydrate in beer by measuring the specific gravity after fermentation. Suppose you have a beer that finishes fermentation at 1.008. First convert specific gravity to degrees Plato dividing the number after the decimal by 4; in this case, that would be 8/4 or 2° Plato. This conversion method is a shortcut but is pretty close to the real thing. A 2° Plato beer contains 2 grams of dissolved solids per 100 mL of beer or 7.1 grams per 355 mL serving (12 ounces). Most of the dissolved solids in beer are carbohydrates so this number could be used as an approximate carbohydrate content.
I keep using the word approximate because alcohol interferes with hydrometer measurements in beer and the real number is higher than 2° Plato. A beer with a normal alcohol content with an apparent extract (hydrometer reading in the presence of alcohol) of 2° Plato, has a real extract (hydrometer reading taken in the absence of alcohol) of about 2.5° Plato. This means that the carbohydrate content is closer to 9 grams per 12-ounce serving.
Carbohydrate content and flavor are related and most beers that have a very low carbohydrate content don’t have much in the way of body and flavor. This is where the joke that compares light beers to sex in a canoe comes from. (You know the one ... “f-ing close to water.”) One notable exception to this rule is with draught stouts. As odd as this seems, draught stouts’ carbohydrate amounts don’t measure up to their mouthfeel.Take Guinness Stout, for example. Guinness draught stout has an original gravity of about 9.5° Plato, contains about 4% alcohol by volume, contains about 120 calories per 12-ounce serving and has roughly 5.2 grams of carbohydrate (data taken from “Stout” by Michael J. Lewis; Brewers Publications, 1995). So why isn’t a pint of Guinness like having sex in a canoe? For starters, stouts get a lot of flavor from the roasted grains, just like a cup of coffee can have rich mouthfeel from dark roasted coffee beans. Also, draught stouts are nitrogenated and nitrogenation adds tremendously to the overall perceived intensity and complexity of the beer. You could also brew a low-gravity amber ale and serve it on mixed gas to do the same thing with a lighter-colored beer.
I wouldn’t recommend brewing an American-style light beer at home because it is actually really hard to brew a beer with almost no flavor. Most light beers are made from highly fermentable worts that leave very little carbohydrate in the finished beer. A long mash rest at 150° to 155° F, the addition of “debranching enzymes” (specifically amyloglucosidase) and high adjunct ratios are some of the common methods used by large brewers to produce light beer.
Unfortunately, most beers do contain a fair amount of carbohydrates. I’m not sold on the whole low-carbohydrate diet for a number of nutritional reasons, but if I were on a carbohydrate-limited diet I would be concerned about my total carbohydrate consumption per day. I’m sure with some budgeting one could figure out how to consume normal beers every now and then without exceeding the daily carbohydrate allowance of the diet. That’s just one beer lover’s opinion.