Bottle bitterness

After recently trying a new beer on draft at a local bar, I liked it so much that I decided to buy a 6-pack at the grocery store. I noticed that the bottled version tasted considerably different. There was much more bitterness and I’ve noticed this with other brands of beer. Why is it that draft beer seems smoother and less bitter than bottled beer? For a homebrewer, is it better to go with a kegging system to achieve this same smoothness or are there some tricks to the bottling process to help the beer keep a smoother finish?

Dan Schipman
Greensboro, North Carolina

I think there are a few reasons why draft and bottled beer taste different and some of the reasons may recolor your view of draft beer. Some breweries actually have different variations of their beers for draft and bottle. I do not have real good information on how prevalent this is, but the examples I am aware of have two commonalities: the draft beer has a lower bitterness and lower carbonation compared to the bottled beer. Sierra Nevada Pale Ale draft beer is different from its bottled cousin in that the draft form is a little darker and has a lower original gravity compared to the bottled version. Both beers are excellent. I assume that their draft Pale Ale is intended to be more of a session beer and the difference in the recipe makes it more quaffable. So this could explain your observation.

Other factors that make draft beer taste different from the bottled can make a brewer an unhappy camper. Some bars put their beers on “beer gas,” also called mixed gas, to “smooth” out beer flavor. An unintended outcome of this practice is that these beers lose their carbonation and deviate from the brewery specification. This really irks me because if a brewer decides they want to serve their draft hefeweizen at three volumes of carbon dioxide, the bar owner or distributor has no business doing something that changes the character of the beer.

In an effort to lower operating costs, some bars use dreadful contraptions called air blenders. This cheap way of making mixed gas creates a mixture of carbon dioxide and air, which replaces nitrogen with the more affordable compressed air. The use of air blenders flatten kegs over time. They also pump oxygen into the keg to oxidize the beer. Sometimes the air compressor hooked to the blender introduces a bit of microbiological wildlife and whatever funky smells are next to its intake into the mix of carbon dioxide, nitrogen, oxygen. In short, air blenders can change the flavor of kegged beer in a variety of different and disappointing ways.

The use of mixed gas and air blenders make bar owners really happy because they reduce beer carbonation, making the beer easier to pour. This practice reduces beer loss caused by the sloppy bartenders slinging pints behind bars scattered across this great land. If I sound a bit harsh towards bar owners and bartenders it’s because that is my intent! The reason that beer advocacy and travel magazines make such a big deal about great draft beer bars is because of the astounding number of really awful draft bars.

Another interesting factoid about draft beer is the flexible line linking the keg to the tap. These little buggers can turn into veritable small intestines. In other words, with their relatively large surface to volume ratio and their tendency to become covered in a microbiological film when neglected, draft lines can turn into long, thin bioreactors that change the flavor of beer as it flows from keg to tap. Neglected taps can also become totally funkified with microbiological growth. This can become especially pronounced with unfiltered beers as the nooks and crannies of the beer tap can quite literally become coated with a visible film of living yeast.

The key to draft beer is really quite simple. Carbon dioxide pressure and beer storage temperature should be matched to the carbonation level of the typical draft beer (usually somewhere around 2.5 volumes of carbon dioxide), and draft lines need to be routinely cleaned. In well-run draft bars, the flavor of draft beer should be within the expectations of the brewery and any difference between a draft and bottled beer should be minimal unless the beer has different draft and bottle specifications.

You mention that you perceive draft beer to taste smoother than bottled beer. This may come from the difference in pouring techniques between the two. It is often the case with draft beer that a noticeable amount of carbon dioxide is “knocked” out of the beer during pouring. In contrast, bottles are easier to gently pour and the amount of carbon dioxide loss is much less. Since carbonation level influences perceived bitterness, any differences in carbon dioxide content between draft and bottle may also lead to apparent differences in bitterness.

As a brewer I prefer draft beer because it is less labor intensive to produce than bottled beer. Recognizing the factors that influence flavor you can adjust your recipe, carbonation level and serving temperature to produce the beer that you want, which is really what homebrewing is all about. And with the proper care and maintenance of your draft system you can avoid many of the problems that readily arise when draft neglect occurs!

Oxygen safety

A few batches ago I switched from using my aquarium pump aeration method to pure oxygen. Thirty seconds with pure oxygen versus 30 minutes with the aquarium pump has been a welcome time saver. I am using a stainless steel wand with an air stone connected to a red 1.4 oz. metal canister of welding oxygen I purchased at a hardware store. In my research before going to this pure oxygen system, I found very little information about the safety of using these welding oxygen canisters. I found one posting on the Web saying that using this, “non food grade,” oxygen is safe because concentrated oxygen kills any possible contamination. Could you tell me if these welding oxygen canisters are safe to use for wort aeration and/or is there a better alternative for pure oxygen?

Bruce Wilder
Brattleboro, Vermont

The short answer to your question is that welding grade oxygen is probably OK for homebrewing. I know that the only difference between medical grade and welding grade oxygen at my local industrial gas supply is the container the gas goes in. Medical grade oxygen must go into containers that are only used for that grade and there are probably some special inspections and filling procedures used for the medical grade stuff. The actual oxygen gas comes from the same bulk tank. My guess is that most gas suppliers use a similar procedure. As far as contaminants from oxygen go, microorganisms are not a concern because, as you mention in your question, pure oxygen is not a very hospitable environment.

I do suggest using caution when using pure oxygen to oxygenate wort. The problem you face is that the solubility of oxygen in wort is much higher when pure oxygen is used instead of air. Most brewing texts cite the ideal level of oxygen in wort prior to fermentation at around 8 ppm or 8 mg/L. Levels higher than this can cause oxidative damage to yeast cells. When using pure oxygen, wort oxygen levels of about 30 ppm are possible, making over-aerating a legitimate concern. One way to meter the flow of oxygen into wort is to use a gas flow meter. Gas rotameters are common and relatively inexpensive devices that measure the flow of gas.

If you have a flow meter, you can use it to meter gas flow and determine the amount of gas required given a few assumptions. Let’s say you want to add 8 mg/L of oxygen to your 20-liter batch, you can see that you will need 160 mg of oxygen (Note to metricphobes: get over it! The metric system is so much easier than our units when doing these types of calculations. No metric to English conversion is offered because chemistry simply cannot be addressed without using the metric system). 160 mg is equivalent to 0.005 moles of oxygen (0.16 grams/32 grams of oxygen per mole = 0.005 moles). If you multiply 0.005 moles by 22.4 l/mole you see that 0.112 liters of oxygen are required to supply the 160 mg required to yield a concentration of 8 ppm in your 20 liters of wort.

I said there are a few assumptions required for this calculation. The first assumption is that all of the oxygen injected in the wort goes into solution. This is not a bad assumption if the oxygen is bubbled from the bottom of the fermenter and the bubbles are really small. A wand with drilled holes (rather than a gas stone) would produce larger gas bubbles which have a reduced tendency to dissolve into the wort. This would be evident as bubbles break the surface of the wort. Assuming 100% transfer is not a bad assumption as long as you use a stone and keep the oxygen flow slow during aeration. The second assumption is that the ideal gas law is valid enough for brewing and that one mole of oxygen is similar enough to an ideal gas that the 22.4 liters/mole (at atmospheric pressure) conversion is believable. In my opinion, the ideal gas law is certainly good enough for brewing. If you are a chemistry guru fell free to use your favorite equation of state.

If you want to buy a gas rotameter look for one that is scaled in liters per minutes (not cubic feet per minute) with a range between 0-1 Liter/minute (lpm) and 0.1 subdivisions. In this example, running the gas flow at 0.2 liters per minute for 30 seconds will introduce about 0.1 liters of oxygen.

Some brewers attempt to replace a gas flow meter with a gas pressure gauge. Without getting into details, I do not recommend using pressure as an indication of flow because it simply does not work well. Unless you know that 10 psi gas pressure delivered to your stone gives some known flow rate you are guessing. The bottom line is that to use oxygen for brewing you really should have a flow meter.

Once you get some experience in introducing oxygen into your wort you can begin making adjustments. If you believe that less than 100% of the gas is going into solution, you can make small adjustments to compensate for the loss. Without measuring the oxygen concentration in your wort this is certainly a guess, but it can be a reasonable one. If you approximate that you are getting 90% of the oxygen injected into your wort, simply divide 0.112 by 0.90 and increase the oxygen volume to 0.124 liters. By using a flow meter you can make small changes with the confidence that accompanies knowing your flow.

We use air for aeration at Springfield Brewing Company. Dry compressed air comes into our aeration panel, flows through a sterile filter, then to a rotameter flow meter before the in-line injection point. Whether using oxygen or air, gas flow meters are handy gizmos to have around the brewery!

Brew Your Own Technical Editor Ashton Lewis has been answering homebrew questions as his alter ego Mr. Wizard for the last 12 years. A selection of his Wizard columns have been collected in “The Homebrewer’s Answer Book,” just released, available online at brewyourownstore.com.