When cold crashing or lagering beer from a relatively warmer temperature to a colder one, negative pressure of condensed air in the headspace can draw in liquid and air through the airlock or blow-off tube. Is this a concern, and how can it best be avoided?
Adelaide, South Australia
I do think the scenario you describe where liquid and/or foam from an airlock is sucked into beer when cooling is a very real concern. Fortunately there are a few things that can be done to prevent this from occurring. If your beer resides in a container with a fairly narrow opening like a carboy with no pressure rating you can equip the neck of your container with a filter for the air that is pulled into the headspace as the contents of your fermenter cool.
Cotton plugs make very effective gas filters and are commonly used in laboratories to plug up the tops of test tubes and flasks used to grow all sorts of cultures. Cotton rolls can be purchased at your local pharmacy and you can make a correctly sized plug to fit the opening of your fermenter. After your fermenter has cooled you can replace the airlock because the cotton plug will allow the beer to oxidize if not replaced. If you are concerned about oxidation and are bothered by the air entering the headspace during cooling you can feed a small gas line into the neck of your fermenter before inserting the cotton plug and start a very slow flow of carbon dioxide into the headspace to create a positive flow of carbon dioxide out of the plug. This process is handy when your fermenter is not rated for pressure.
If your fermenter can tolerate a bit of pressure you have other options. A good question to ask is “how do I know if my fermenter can handle pressure?” Pressure rated vessels, like stainless steel homebrew fermenters, soda kegs, and beer kegs should be clearly labeled with the rating of the vessel. Plastic and glass containers are another story and are typically not individually labeled; this does not mean that they have no pressure rating, but determining the rating can be difficult. Plastic containers can certainly withstand some pressure, but glass containers, especially flat-bottomed carboys, can easily be broken with very little pressure. For this reason always assume glass containers have no pressure rating unless you have convincing evidence that they are pressure rated.
OK, so let’s assume your fermenter can tolerate a bit of pressure. Instead of using a cotton filter you can simply close your fermenter’s vent valve and pressurize the headspace with carbon dioxide to about 5 psi (0.3 bar) before moving your beer into a cooler environment. This headspace pressure is sufficient to seal an inward opening lid that requires internal pressure for sealing but low enough to not add significant carbonation to your beer. Since carbon dioxide is being used in this method, the gas pressure will decrease as the gas is absorbed by the beer; this means that the gas line needs to stay connected to the fermenter. If you do not want your beer to become even slightly carbonated during the cold aging step, simply disconnect the gas from the fermenter after it has cooled and equip with an airlock, and the beer will re-equilibrate with atmospheric pressure.
I have been writing this column for the past 21 years and have addressed this topic several times because it is an important consideration and is often overlooked. If a survey were conducted to determine the most relevant commonality among great beers the result would certainly be rigorous attention and understanding of cleaning and sanitation. Sometimes very clean breweries have microbiological issues. These problems can be very challenging to track down, but when they are identified and solved the root cause is frequently something that seems very basic. Preventing airlock suck back is one of those basic things that can throw a monkey wrench into an otherwise clean and tidy operation.
We all (hopefully) know not to bottle-carbonate beers beyond a certain volume, such as 2.5–3 volumes. Say that you have a highly carbonated brew (3.5–4 volumes) that you force carbonated in a keg and now want to bottle from the keg. If you bottle into a regular 12 oz. bottle will there be any issues with the CO2 coming out of solution if the bottle is at room temperature? Or can you pull this off safely since the beer is already carbonated vs. what happens as yeast eats sugar when you bottle-carbonate?
Most bottled beers do fall into the 2.5 to 3.0 volume carbonation range, but there are styles that are typically carbonated to a much higher level. Many Belgian styles and German hefeweizens are normally carbonated to a higher level, sometimes pushing the 6 volume mark, and Champagne often times contains more than 8 volumes of carbon dioxide. The most important thing when bottling beers with higher carbon dioxide levels is selecting glass bottles that have a pressure rating aligned with the pressure developed in the bottle. Violating this basic rule results in exploding bottles; a safety problem and a product loss problem all in one.
So you want to have bottled beer in the 3.5 to 4.0 volume range and your plan is to carbonate in a keg and then bottle. I will address this question shortly, but will start with the easiest method first. And that method is bottle conditioning because you do not have to transfer the beer from keg to bottle. Whether you keg condition or bottle condition, the pressure rating of the bottle must be high enough to cover the possibility that the bottle is exposed to high ambient temperatures. Ordinary beer bottles are designed for use with beers with up to about 3.0 volumes of carbon dioxide, but since ordinary beer is pasteurized in a tunnel pasteurizer an ordinary beer bottle must be able to withstand well over 100 psi of pressure. Compare this to the 80 psi of pressure required to keep 5 volumes of carbon dioxide in solution at 80 °F (27 °C) and you can see that most beer bottles can be used for a very wide range of beers, as long as the beer is stored in a temperature-controlled home environment. Even so, it’s the norm to use heavier bottles — think sparkling wine heft — for beers carbonated in the 3.5 volume range because consumers buy beer in stores and then transport the beer in cars that can become very hot, resulting in increased bottle pressures during the warmer months of the year. This scenario can result in growler bombs and big messes since most growlers have low pressure ratings, but that is the subject for
In your case you have a keg of beer in the 3.5 to 4.0 volume range and you want to move it from keg to bottle. The tool for this job is a counter-pressure bottle filler that will allow you to: 1) Open a gas valve to pressurize the bottle with carbon dioxide to the same pressure as your keg, 2) Open a fill valve connecting the keg and bottle, and 3) Open a vent valve allowing carbon dioxide to escape as beer fills the bottle. When the bottle is full, the beer supply valve is closed, the headspace pressure is slowly relieved, the fill tube is removed and the bottle is capped. The trick is to do all of this with minimal oxygen pick-up and minimal foaming. Excessive oxygen pick-up during filling results in accelerated beer oxidation and foaming during filling results in beer loss and low-fills, bottle-to-bottle variation. Sometimes foaming is severe enough to make capping a nearly impossible task and this situation quickly becomes very maddening.
The thing to remember about carbonated beer is that when the pressure in the container is released, for example when opening a bottle or can of beer, the beer is supersaturated with carbon dioxide. Supersaturation means that the beer contains more carbon dioxide than allowed by the pressure and temperature of the system and the system will adjust to the saturation level associated with this new pressure and temperature condition by losing gas. When you gently pour beer from a pressurized container into a glass there is minimal foam formation and when the beer is left alone it slowly adjusts to this new condition over time. In plain terms, the beer goes flat. Compare this mental image of tranquility to what happens when roughly pouring a bottle of beer into a warm glass with a healthy dusting of salt granules in its bottom . . . you should be seeing a beer volcano that ends with half of the beer sitting on the bar top around the glass and the other half of the beer streaming bubbles of carbon dioxide into the environment. Beer gushes, or quickly releases carbon dioxide, when it is supersaturated with carbon dioxide and is treated in such a way that causes the beer to foam. Once foaming begins it builds upon itself since a gas bubble is itself a nucleation site for more gas bubbles to form.
There are numerous things that can make bottling difficult, but they all relate to the beer volcano scenario described above. The most basic rule of bottling is to start off with very cold beer. If you don’t have cold beer in your keg you are setting yourself up for trouble. Turbulent flow between the keg and bottom of the bottle is the equivalent of the rough pour, causes localized changes in liquid pressure and can result in foaming. This frustrating situation is often seen at bars where a rough spot in a draft line, often associated with a dirty line, or a rough transition causes beer to froth and sputter from the tap as the bartender struggles to fill the glass. This means your filling rig needs to be well made to minimize turbulence and kept very clean as dried beer leaves rough surfaces.
Another major cause of gushing during bottling is low headspace pressure in the bottle. This can happen if your regulator is set too low, or if you release the gas too quickly during filling. The thing about bottling that is quite different from filling a glass is that a very small amount of foam presents a very real problem because bottle necks are narrow; once foam rises into the neck and spritzes out of the gas relief valve more foam is often formed in the neck, resulting in slow filling and beer loss. The goal is to quietly fill the bottle all the way to the fill level without any foaming. Controlling gas pressure goes a very long way to accomplishing this goal. If you control the filling process correctly, you can induce a slow and predictable release of carbon dioxide after the bottle is full and before the cap is sealed. This is known as crowning on foam and is an effective means of reducing oxygen pick-up from the air that enters the bottle headspace when the filling tube is removed. One way to do this is to gently knock a full bottle of beer that has been quietly filled right before capping; that gentle knock causes gas to escape and foam the bottle. You can also do this as a rude party trick to set off bottle volcanos at will.
And the last group of factors relate to the condition of the glass. Rinse your bottles before filling. Wet glass is much, much smoother than dry glass and commercial bottle filling operations always fill beer into bottles that are rinsed immediately prior to filling. Not only does rinsing make the surface smoother it also rinses off dust that may be present on the glass surface; dust is like a salt crystal and will act as a nucleation site if present on the bottle surface.
Warm or hot bottles can also cause problems, especially when bottling beer with higher levels of carbon dioxide. Although commercial bottling lines work quite well with room temperature bottles, rinsed with ambient water, chilling glass at home is something that can be done if the need arises. This is not practical on a larger scale.
And the last major problem associated with glass is surface roughness associated with reused bottles that have either been etched by too many washes with aggressive detergents or reused bottles that have not properly been cleaned. Happy bottling!
I bought a Blich-mann HopRocketTM after visiting a local brewery and being floored by the tremendous hop flavor. They used Azacca® hops in an IPA. I used my HopRocketTM on a Blind Pig clone with my homegrown Centennial hops. To my surprise I got no hop flavor at all. It tasted like tea. So I next tried it with Azacca® hops on a Kitchen Sink IPA. More tea. What gives?
The HopRocketTM is an in-line hopping device intended for use with whole cone hops. These types of brewing tools can be used between the kettle and wort cooler for aroma additions, similar to how commercial breweries use hop backs, used for dry hopping after fermentation like Sierra Nevada’s hop Torpedo using a recirculation pump, and can also be used in-line between keg and tap like Dogfish Head’s Randall. Cool tools definitely allow certain things to be done in the brewery that are otherwise not possible, but cool tools alone don’t always solve a problem. In the case of your HopRocketTM the other part of the equation is good hops.
This is a touchy subject, especially when the hops in question are homegrown. The fact is that not all hops are created equally. The same hop variety grown in the same valley can have different properties based on microclimate differences, or the terroir, and time of harvest. Climatic differences covers variables such as soil type, sun exposure, rainfall, temperature, humidity, and elevation within a valley. Add age and storage temperature, and the result is a wide range of aromas from the same variety, grown in the same region and harvested in the same year. When the same hop variety is grown in different parts of the world the result is often so different from one region to the next that the hops may as well be different varieties.
Homegrown hops can be a challenge because high quality hop cones are much harder to produce than hop plants are to grow. I remember listening to a talk given by Val Peacock a few years back at a Craft Brewers Conference in San Diego. Val is one of the most knowledgeable people in the hop world and was the hop guru at Anheuser-Busch for many years. A question from the audience suggested that local hops from San Diego were better than hops from the Yakima and Willamette Valleys simply because they were local. I think I saw hackles begin to stand on the back of Val’s neck when he remarked on the knowledge and skill the hop growing families in the US, some with 5 generations of experience, have with coaxing the best out of this unusual plant. I may be totally incorrect and out of line here, but your homegrown Centennials may not have been up-to-snuff with Centennial hops grown in Washington State. Your locality is not a bad place to be growing hops and you may have ended up with a grassy aroma because of the way the hops were dried and stored after harvest.
You then used your HopRocketTM with Azacca® hops and again the result was less than spectacular. These two experiences are not great news, but they are the type of disappointment that can have a positive spin. The spin I am going to put on it is that you probably will never look at a bag of hops the same again. You were expecting massive citrus and piney from your Centennials and tropical fruit with lots of mango, papaya, and citrus from the Azacca®, but both varieties only contributed grassiness. This really sounds like a hop quality problem.
The truth is that aroma hop varieties are in really huge demand these days and sometimes what can be bought is not always the best hops. Why? Because commercial brewers who participate in hop harvest selection usually buy the cream of the crop and leave the rest for what is known as the “spot market.” There are lots of great hops available on the spot market, but there is also a fair amount of ho-hum out there. Observing hop color, smelling the aroma in the bag and rubbing a small sample to release aromas will help you evaluate hops. Hop evaluation requires certain skills and these skills are developed by doing. The best way to start learning how to evaluate hops is simply to begin observing, smelling, rubbing, and brewing, and then noting what works. Don’t give up on using your HopRocketTM, but the next time you are ready to load this bad boy up with hops, give your hops a good evaluation before using. If you don’t like what you have, don’t use them. Bad aroma hops can definitely ruin an otherwise excellent brew.