Carbonating High-Alcohol Beer, CO2 Protection & Filtering: Mr. Wizard
Q
I fermented a Russian imperial stout for 10 days, held in the secondary for 20 days, and did a third transfer/conditioning for 30 days. Next, I transferred it into a freshly emptied bourbon barrel for 8 weeks. It clocked in at 13.5% ABV. At bottling time I added the same yeast I used for fermenting to the bottling bucket with the beer and priming sugar. The beer never carbonated. What should I have done to carbonate this beer? Did the high ABV overwhelm the yeast?
Bill Bartman
Portland, Oregon
A
It’s really pretty amazing how the beer scene in the US has changed so much that barrel-aged beers have generated great interest and tremendous success among brewers playing with barrels. Barrels do present many challenges not encountered with the brewing of other types of beer. And carbonation after barrel aging is one of those challenges.
I am not going to pretend to know all of the reasons that barrel-aged beers are often difficult to carbonate using normal methods, even when fresh yeast is used. But the two real big issues about these beers are mentioned in your question, and those are high alcohol and very low yeast viability, and cell density following
prolonged aging in multiple vessels. I have read that some yeast strains are more or less active in the presence of oak tannins, especially with new barrels. Not sure about how bourbon barrels factor into this calculus. Here are a few ideas of how to carbonate high-alcohol beers with very little to no viable yeast that is in the proper health to contribute much to the effort of carbonation.
The first is to deliver a dose of yeast that is in the proper condition to do the job required. I am fond of kräusening because actively fermenting yeast are in the proper biological condition to convert carbohydrates into carbon dioxide quickly and efficiently. This is different from adding dormant yeast (for example, dried yeast) and sugar to a bottle of beer. Dormant yeast have to “wake up,” prepare for metabolic activity, transport carbohydrates across their cell walls and crank up the metabolic machine before any carbon dioxide is produced. This is referred to as the lag phase of cell growth and occurs before microbiological cultures begin growing. The bottom line is that adding yeast that are awake and making noise gives you a better shot at carbonating these beasty brews than adding inactive yeast.
The type of yeast can also be a real factor with higher alcohol beers. Years ago I questioned the alcoholic strength claimed by many brewers and chalked some of the high claims to a blend of bravado and faulty math. Not so today as the art and science of high alcohol beer brewing has become better understood. Add to this the alcohol contributed by wet bourbon barrels, for example, and brews topping the scales at 13.5% ABV are not such an oddity. The alcoholic strength of your beer is surely a problem for many yeast strains. The use of a more alcohol-tolerant yeast, like Champagne yeast, is definitely worth considering for these beers high in ABV. Be careful, though. Your beer may have some residual fermentables if the fermenting strain was not able to deal with the high alcohol. Adding a different strain at bottling time could present an issue with excess carbonation and bottle bombs if your beer has a lot of residual fermentables. This may not be an issue, but is something to keep in mind. You could do a small test fermentation if you have serious concerns.
I have saved the easiest, and least sexy suggestion, for last. Rack your beer into a keg, add carbon dioxide head pressure to add the level of carbonation you seek, and use a counter pressure bottle filler to fill your precious beer into bottles for safe keeping. The real advantage of this method is that the level of carbonation can be checked prior to bottling and the potential for over-carbonation or under-carbonation due to bottle fermentation issues is about nil. What I like about this method is that the beer flavor profile is more-or-less set when you bottle, and that the flavor changes that occur during aging have little, if anything, to do with changes in carbonation. Hopefully this information is useful to your endeavor!
Q
I always hear that CO2 is heavier than air, but I am no scientist. Just how much heavier than air is it? I would like to know if the method of injecting a little CO2 into a carboy before transferring or blasting a little into a bottle before bottling has any impact on keeping the oxygen out of your finished beer? I have a vision in my head of this blanket of CO2 sitting in the bottom of a carboy or a bottle, then filling them from the bottom up where the beer nicely stays under the blanket of CO2 and eventually all the oxygen gets pushed out as the level rises in the carboy or bottle. Is this really what is happening?
Bill Serowski
Hamburg, New York
A
Oh boy, this topic is one that I have some pretty strong thoughts about! I will start by throwing out a few numbers to answer your question about gas weight and density. Carbon dioxide weighs 44 grams/mole, oxygen weighs 32 grams/mole, and nitrogen weights 28 grams/mole. Since air is about 79% oxygen and 21% nitrogen, the weighted average comes out to be 31 grams/mole. According to the Ideal Gas Law, an “ideal gas” occupies 22.4 liter per mole at atmospheric pressure and 0 °C (32 °F). I will leave the discussion about how this assumption is problematic for engineers to physical chemists. The take home message is that there is certainly a difference in density between carbon dioxide and air, with air having only 70% of the density of carbon dioxide.
To put this density difference into perspective, ethanol has a density of 0.79 kg/liter, compared to 1 kg/liter for water. If you carefully pour ethanol on top of dyed water (using a handkerchief helps this experiment) you can easily float ethanol on top of water (the dye in the water helps visualize this effect). The same is true if you carefully “pour” carbon dioxide on the bottom of a container of air. The problem is convection.
Take your glass of dyed water with the ethanol cap and heat the bottom of the glass with a hot plate or heat source of your choice. The water will begin to move around because of convective currents and these currents cause some mixing to occur at the interface between the water and the ethanol. If the layer of ethanol is really thick you will end up with water on the bottom, a mixture of ethanol and water in the middle and ethanol on the top. If the ethanol layer is thin, the glass will completely mix due to convection. If you did the same experiment with oil and water, the oil would always float on top of water because the two liquids are immiscible.
Gases do the same thing when there are differences in temperature in the system, for example the carboy and the gas being added to it, and gases don’t behave like oil and water. This means that gases mix and tend not to layer. Add Brownian Motion to convection and what results is a system that will eventually equilibrate. Carbon dioxide can effectively be used as a blanketing gas if it is carefully added to the bottom of containers (carefully means low velocity to minimize mixing) and quickly used to guard against oxygen ingress into beer. In order to do this it is important to create the blanket and fill beer beneath it before the blanket is infiltrated by air.
So how can this be applied to homebrewing? For starters, if you do want to blanket a carboy or bottle with carbon dioxide you need to add the carbon dioxide to the bottom of the container. If you add it to the top of the container it will sink and mix with the air and never form a solid layer at the bottom. And if you use this method you need to diffuse the flow. A gas diffuser stone works great for this method. A cheap aquarium stone slipped onto the end of a gas stone will do the trick.
But how do you know that this works? Unlike the water/ethanol demonstration you cannot conveniently dye gas and there is always a level of uncertainty without the use of an expensive gas meter. My go-to method is to fill a container to the brim with water and then push the water out using carbon dioxide. While not practical for bottle filling, this method is both practical and very effective for purging kegs and beer serving tanks. We use this method to prepare our 500-gallon (1,900-L) serving tanks for filling at Springfield Brewing Company.
The water we use is recovered, so the only thing our method requires is time to fill our tank with water and then to displace the water with carbon dioxide. Other breweries layer carbon dioxide into the bottom of their tanks.
I know our method seems pretty extreme, but I am not convinced that we use any more gas than we would if we attempted to flood the tank with carbon dioxide while displacing air in the process (a relatively common method). My former day job with the Paul Mueller Company has exposed me to some really interesting processes over 18 years. We have built numerous million-gallon (3.8 million L) aseptic orange juice storage tanks over the years and that industry is very concerned about oxygen because oxidized orange juice takes on a brownish color and loses Vitamin C in the process. These huge orange juice tanks are flooded with 1 million gallons (3.8 million L) of iodophor, then pushed out with sterile nitrogen and completely drained prior to filling. This method not only displaces all of the air from the tank, it also ensures complete contact of the sanitizer with the tank wall. Thanks for the great question!
Q
Oxygen absorbing caps — I can’t find any science behind them. How does something “absorb” O2? Do they actually work and where’s the evidence?
Nathan Hoskins
Lexington, Kentucky
A
Not 100% sure what the crown liners contain, but do know they work. Plenty of data and anecdotal evidence shows that these special liners reduce oxygen ingress and help to scrub oxygen from the headspace. Two common chemistries used to give polymers oxygen-scavenging properties are the inclusion of iron or ascorbic acid in the polymer mix. These compounds bind oxygen, and that’s basically how they work.
The topic I did not mention in my original answer was oxidation in general, and especially oxidation associated with bottle filling. Much has been written in the homebrewing literature about hot side aeration in the brewhouse and splashing of beer causing oxidation during racking, but there seems to be less written about oxygen pick-up during packaging. The truth is that oxygen pick-up during packaging can very quickly ruin great beer and is certainly a topic worthy of serious head scratching.
In the commercial world of brewing there are really two types of bottling operations. Small-scale fillers that operate in the 2–50 bottle per minute range and rotary fillers that typically are designed to run in the 100–1,000 bottle per minute range. The modern rotary filler incorporates bottle pre-evacuation techniques, bottle fill control, and fobbing immediately before crowning to keep oxygen pick-up during filling to amazingly low levels. Many breweries using these sorts of fillers routinely have 50 parts per billion or less of oxygen in bottles after filling. This is really low. These brewers are happy campers.
Slower speed fillers are typically designed for smaller breweries with budget constraints, and many of the technological features common in modern rotary fillers are either less sophisticated in these slower machines, don’t work as well as the faster machines, or are simply not part of the design of the machine. This means that air pick-up is almost always higher, often by a factor of 10, compared to faster and more sophisticated fillers. This is pretty high. These brewers are often times bothered by bottle air.
It seems obvious that these small breweries should just buy fancier technology if they are really concerned about air pick-up, right? Obvious, yes. Easy, no; the difference in cost between these technologies starts at about $100,000 and can quickly be over $1 million. That’s why many small breweries use bottle crowns with oxygen absorbing liners. While these special liners can help small breweries with less than adequate bottle fillers, they cannot perform miracles.
These special crowns are also used by breweries with modern fillers because of oxygen ingress. This happens when oxygen from the environment slowly equilibrates with the carbon dioxide headspace of a beer bottle. Oxygen scavenging crowns help to prevent oxygen from making its way into the headspace and prolonging beer shelf life. So that is why this question brings up an important point worthy of further explanation. Thanks Nathan!
Q
Should I filter when I transfer to reduce sediment in my bottles?
Chad Nixon
Salt Lake City, Utah
A
Filtration at home is not the first thing I would consider doing to reduce sediment in bottled beer. The easiest thing to do (if you can do this) is to move your carboy to a refrigerator for one to two weeks after primary fermentation is complete to let gravity do its thing. If you are using powdery yeast (not flocculent) try using a fining agent. There are some products on the market today that are really effective and easy to use, for example BioFine.
This just happens to be a topic of particular interest to us at Springfield Brewing Company (in Springfield, Missouri) at the moment. Filtration is one of those love/hate things with some brewers, and some tend to love or hate filtration more than others. At Springfield Brewing Co. we have always been pretty neutral on the topic because we have a nice filter that is not a total pain in the neck to operate (not true of many filters found in brewpubs) and we offer both filtered and unfiltered beers. But beer filtration certainly has some drawbacks and we have been debating the pros and cons more lately.
The main problems associated with filtration are beer loss, the potential for oxygen pick-up and aroma and flavor loss, especially with hoppy beers. The major advantage with filtration is clear beer. Clarity really has a few components to it. On the surface, many consumers simply prefer clear beer because that’s what they are used to drinking. Some consumers don’t mind cloudy beer, but do mind chunks of yeast. Even clear beer in a bottle can have a layer of yeast on the bottom that can become chunky when poured, depending on the properties of the yeast and how the bottle was poured. Filtration addresses both of those issues, but at what cost?
On a commercial scale, filtration adds production costs in the form of labor, filtration materials and beer loss.
Filtration also removes yeast, which is kind of the idea, but unfiltered beer with yeast is less prone to oxidation issues associated with air pick-up during filling than are filtered beers. Filtration also prevents bottle conditioning unless yeast is added back after filtration. Sierra Nevada is an example of a brewery that does the latter.
So back to the original question about filtration and my original answer. Filtration is not the first thing
I would suggest for homebrewers because filtration seems much simpler on the surface than it is in reality.
And from a cost point-of-view, there are much cheaper, simpler and generally effective methods available to
the homebrewer. Namely, cold conditioning in a keg or carboy and the use of finings.
The truth is that gravity is an awesome beer clarifier in that its force is great enough to cause yeast cells, and yeast flocs when fining agents are used, to settle out in a keg or bottle. The reason that gravity clarification is not common in large commercial brewing operations is that tanks are too deep for this method to happen in a reasonable timeframe. Homebrewers and small craft brewers do not have this problem. And the more I write about this I wonder if filtration would be the second or third thing I would suggest to a small-scale brewer in search of clear beer. Hmm, that patience thing is coming to mind.
Consider this; the biggest change in beer clarification technology used by medium and large craft brewers over the last 20 years has been the use of centrifugation. Beer centrifuges are continuous devices, some may describe them as bubbles in pipelines, that spin liquid at an angle. This increase in angular velocity increases the gravitational force within the centrifuge and increases the rate of yeast sedimentation. Cloudy beer enters one side of the centrifuge and exits through a different port, seconds later, almost completely clear. Some breweries use a polish filter to make centrifuged beer even clearer and others package without further clarification. The centrifuge only speeds up what can be accomplished at home in a few weeks in a cold environment.
