Over-Carbonating Bottles, Increasing Efficiencies, & Aerating with Oxygen: Mr. Wizard
Q
I have been having problems with over-carbonation in my bottles. I give my batches plenty of time to finish the secondary and check the hydrometer reading to be sure the fermentation is done. Then i add 5 oz. (0.14 kg) of corn sugar and wait about two weeks before sampling the first bottle. It is almost always over-carbonated and nearly all foam. What am I doing wrong? My brewery is at 4,000 feet, could my altitude be the problem?
Talley Pollard
Little Switzerland, North Carolina
A
I think your problem is too much sugar added for bottle conditioning. But before I jump into this topic, I want to focus on the state of beer when it is opened. All carbonated beverages are super-saturated with carbon dioxide, meaning that there is more CO2 in solution when the container is opened than permitted by the atmospheric pressure outside of the container. This is why carbonated beverages are fizzy when the pressure of the container is released.
In the case of beer, carbonation levels up to about 3.5–4.0 volumes or about 7–8 grams of carbon dioxide per liter cause little problem when a bottle or can is opened. Most beer in the world contains somewhere between 2.5–2.8 volumes of carbon dioxide (~5–5.6 g/L) and bottle conditioned styles from Belgium and German weizen beers are often in the 3.5–4 volume range. These beers do not typically gush, even when opened at higher elevations. I have enjoyed many a fine beer on the tops of mountain peaks without major incident.
The thing about super-saturated liquids is that anything that is a nucleation site can cause rapid and seemingly explosive gas release. A fun parlor trick in the kitchen is to heat water in a very clean stainless steel pot with fairly pure water. If you control things just right, which typically happens by mistake, you can cause water that is hotter than the boiling point, but not yet rolling, to gush into steam by tossing in a packet of powder or something as innocuous as a tea bag. The same sort of thing occurs when soda is poured over coarse ice cubes or beer is poured into a glass containing a few salt crystals. But under normal conditions, a bottle of beer can be opened and poured without too much fanfare.
So now it’s time to take a huge turn in the flow of this question. And that is onto the topic of why the metric system makes problem solving easy. Bet you didn’t see that one coming! Above I slipped in the metric equivalent to the volume, which is a unit that both makes sense and no sense at the same time. A liter of beer containing 3 volumes of carbon dioxide would fill a balloon with 3 liters of carbon dioxide if all of the carbon dioxide were driven from solution. And this cannot happen under atmospheric pressure. And doing any simple math with this weird term is simply not feasible. The metric system solves all of these problems.
Hold onto your bottle opener! When one gram of glucose is fermented by yeast (assuming 100% efficiency), 0.49 grams of carbon dioxide is produced. When you add 5 ounces of priming sugar (corn sugar, aka glucose) to your bottling bucket (I am assuming weight here, not 5 ounces of volume) you are adding 142 grams of glucose. And when that glucose is fermented by yeast during bottle conditioning it yields 70 grams of carbon dioxide. Add in the assumption that your nominal batch size is 5 gallons or 18.9 liters, this equates to 3.7 grams of carbon dioxide per liter of beer attributed by the priming sugar. But beer after fermentation and cold conditioning, even at atmospheric pressure contains at least 3 grams of carbon dioxide per liter of beer, bringing the total up to about 6.7 grams per liter, or 3.4 volumes in US terms. This is a wee bit on the high side of things, but nothing to give huge concern.
The assumption above about your hypothetical carbonation level assumes a beer volume of 18.9 liters (5 gallons). If you fiddle around with the numbers in my logic above with your actual bottling volume, say 15 liters, you will discover that you may have about 8 g/liter or 4 volumes of carbonation in your beer. This level of carbon dioxide coupled with your elevation very well could lead to gushing bottles, especially when dealing with beer that is likely to contain more yeast solids (nucleation sites) than commercial beer.
The basic problem is likely a result of using too much priming sugar. But the underlying problem, with this and others, may be that weights and measures cited in recipes are all based on wort and beer volume. If you follow a recipe for a 5-gallon (19 L) batch of beer and end up with only 4 gallons (15 L) the ingredient additions that are pegged to beer volume need to be adjusted. Likewise, if you are adding hops based on 10 gallons (38 L) of wort after boiling and you predict only ending up with 8 gallons (30 L), you should reduce hop additions by 20%.
Whenever I encounter a problem that simply does not add up, the first thing that comes to my mind is the accuracy of measurements. Many homebrewers don’t measure a lot of things because of the seemingly precise instructions of recipes. My bet on the cause of your problem is in part, if not entirely, due to assumptions made about beer volume at packaging, the weight of sugar required for the job and/or the relationship between sugar volume and sugar weight.
Q
I am looking for ideas to help me get more yield from a batch of my homebrew. I figure the time spent for mashing (I brew all-grain), fermentation, racking and packaging all take about the same amount of time whether I net 5 gallons (19 L) of beer or 4 gallons (15 L). My problem is that I never get anywhere close to 5 gallons (19 L).
Tim Jennings
Chicago, Illinois
A
This question reminds me of a phone call I once received from a winemaker who was considering building a brewery, and the plan was to build a 400-barrel brewhouse (12,400 gallons per batch). This made my ears perk up as I was thinking that the brewery in planning would have an annual capacity of at least 500,000 barrels per year. I was wrong. The idea this fellow had was to install very large equipment and only brew once a week. While this may be appealing from a labor point of view, the capital investment required for this person’s sort of plan is impossible to justify based on labor savings over a rational time frame. But the general concept does indeed have merit.
The first thing I would consider is to brew larger batches if you want more beer for one very simple reason; there is always some loss encountered during brewing. If you simply want to improve your efficiency for the challenge involved, that’s one thing, but if you feel like you are not generating enough beer from a batch to justify the time required or to satisfy your demand, brewing larger batches can help address that problem.
But there are some techniques to help improve the yield from a batch. The most common sources of loss in brewing are encountered during extract recovery from malt (mashing and lautering), wort loss associated with hops and trub, and beer loss associated with foaming during fermentation, yeast, racking and/or filtration, packaging and beer dispense. The most common topic discussed by brewers is brewhouse yield. Although this is an important topic for a number of reasons, such as ability to formulate new beers, ability to consistently brew and economic considerations, poor brewhouse yield does not equate to loss of volume. A brewer with an inefficient brewhouse can make up for this by simply using more malt than a brewer with a more efficient brewhouse to produce the same wort volume.
As the popularity of very hoppy beers continues to spread, brewers continue pushing the hop addition envelope. One of the huge downsides to some of the methods being used is wort and beer loss. Wort loss increases in the whirlpool process used to remove pellet hop solids when hopping rate increases and beer loss increases during racking when dry hopping is used. Some large commercial brewers are using centrifuges to reduce wort loss after whirlpooling.
Although this method is out of the reach of the homebrewer, and most small commercial brewers, the idea is pretty simple; recover wort typically discarded with hop solids. An easy and relatively inexpensive method that can be used at home is to collect the trub and separate the wort from the solids using an Imhoff cone. I will leave the details of this method for another day, but this basic idea will definitely reduce loss. Kettle finings, e.g. Irish moss, are very effective at increasing the density of protein flocs precipitated during boiling and improve the separation of trub from wort. And if you really want to push the homebrewing envelope, the use of hop extracts can all but eliminate hop solids from the whirl-pool process . . . there is much more to using hop extracts than simply replacing hop cones or pellets with extracts, so calm down if this seems like a silver bullet!
Beer loss during fermentation is so common that many brewers assume that “blow-off buckets” are a requisite of a well-appointed brewery. This sort of loss drives me crazy and is not limited to homebrewing. While tepid fermentations with little activity are often indicative of real problems with yeast pitching rate or yeast health, fermen-tations that gush beer from the top of the fermenter are certainly not models of perfection. Properly sized fermenters are large enough to accommodate foam, designed to safely vent carbon dioxide out of the fermenter and permit the beer to ferment with-out losing product. This is easy to address by simply using a larger fermentation vessel. There are some fermentation methods that are designed to skim brandhefe (literally translated as “burned yeast”) or braun hefe (brown yeast) from fermenting beer. These include Yorkshire Squares, Burton Unions and a variety of lager fermenter designs with foam chambers, but all of these methods are designed to minimize beer loss, whereas the blow-off bucket is simply a method to control the mess associated with this unmanaged loss.
Racking loss is a loss that is pretty difficult to eliminate because the greatest source of the loss is beer tied up with the yeast at the bottom of the fermenter, and unless a centrifuge is used to separate beer from yeast, this loss is always present. Racking loss can be minimized, however by selecting yeast strains that have good flocculation traits that lead to thick sediments that are easy to leave behind in the bottom of the fermenter.
Like wort loss, racking losses are affected by hopping. Dry hopping is a great method, but with it comes inherent losses. There are numerous methods being explored by some of the larger craft brewers to address this very real and expensive loss. Additionally, the traditional method of simply adding hops to the fermenter is not the most efficient method of extracting hop aroma compounds. So the losses are two-fold when it comes to dry hopping, and both forms are expensive. Some of the newer dry hopping methods include containing the hops in a small vessel through which beer is pumped, for example, the Torpedo method developed by Sierra Nevada, hop removal using a centrifuge, and methods aimed at increasing the aroma yield from pellet hops by more effectively dissolving the pellets prior to addition. Many brewers are also looking at hop extracts to address these issues.
And finally there is loss associated with packaging and dispense. Most homebrewers are either bottle conditioning or kegging their beers and these methods typically do not result in high packaging losses, as compared to packaging carbonated beer. Beer dispense, however, frequently does result in high losses that are, for the most part, entirely controllable. The use of refrigerated keg boxes, “jockey boxes” with cold plates or cooling coils, and the elimination of sections of beer line exposed to ambient temperatures help to reduce foaming associated with warm lines. Proper pouring techniques — specifically the implementation of patience — help to further reduce dispense losses. Emulating the practices seen in most bars where bartenders pour foam down the drain is something to avoid since beer foam is about 50% beer. If a foamy pour is allowed to settle and patience is used during dispense, losses, which typically hover around 10% for many bars, can virtually be eliminated at your home bar.
Q
I am looking forward to begin aerating high gravity worts with pure oxygen. First, I’ve read that one should use a pediatric oxygen regulator designed to deliver low flow rates with an incorporated flow meter to accurately assess and control the amount of oxygen being delivered into the wort. where can such a regulator be purchased? Second, does a 2 micron diffusion stone work just as well as a 0.5 micron stone? Finally, at what original gravity (OG) does it become necessary to aerate with pure O2, and how long should a flow rate of ~1 L/minute be delivered to these high gravity worts?
Kevin Koehntop
Salt Lake City, Utah
A
Before jumping into the mechanics of oxygenation, I want to touch on oxygenation versus aeration. Yeast require oxygen to grow since oxygen is a component of healthy cellular membranes. When brewing fermentations are lacking in oxygen, fermentation rate, yeast health, and beer flavor are all affected. The simplest and cheapest way of adding oxygen to wort is through aeration, since air is comprised of 21% oxygen. The primary challenge with this method is that the solubility of oxygen from air is about 8 ppm (8 mg/liter) in 12 °Plato wort and begins to drop as wort gravity increases. This is not a major problem up to about 18 °Plato if you have a good aeration method and plenty of healthy yeast. For these reasons, many brewers prefer using oxygen instead of air as the source of oxygen when brewing higher gravity brews.
One major difference between aeration and oxygenation is that the latter requires more control because the aeration method cannot result in too much oxygen in wort, but using pure oxygen can. Practical experience from brewers who routinely oxygenate wort demonstrates a range of real issues with excess oxygenation. Fermentations often begin vigorously with lots of yeast activity and growth, but end up stalling before fermentation ends. And yeast harvested from these batches has lower viability and vitality compared to yeast from batches with less oxygen going into fermentation. Beer aroma is also affected by wort oxygen levels — with increased sulfur production and reduced ester production being two flavor notes associated with increased oxygen. To complicate the discussion, all of these factors are yeast strain-dependent. The bottom line is that yeast need oxygen during the early stages of fermentation and more problems result from insufficient oxygen than too much.
I have used the sort of set up you describe to oxygenate yeast during propagation and think I can give you some helpful pointers about this method. I totally agree with the idea that oxygen should be delivered at a low flow rate. This really does two things for you. The first is that the low flow rate, especially when put through a small diffusion stone, can result in nearly 100% transfer of the oxygen into solution. I will get back to the significance of this in a moment. The other practical result of oxygenating at a very low flow rate is that you can more easily time and control the oxygenation process, where small variation in oxygenation time have little effect on the process. I don’t have any data comparing the performance of 0.5 micron stones to 2 micron stones, but believe based on the availability of sintered stones intended to facilitate gas diffusion that pores in this size range work well for the application. The system I built for small scale yeast propagation (30 gallon/114 L batch sizes) used a 2 micron aeration stone.
So let’s begin with the type of regulator. The regulator I purchased for my project was a medical-grade regulator made by Victor, with a regulated flow range from 16 mL/min. to 500 mL/min. The advantage to producing a very slow and steady gas flow through porous stones is that the small bubbles release from the surface of the stone and flow as small bubbles into the liquid mass. If the flow rate is too great, the bubbles have a tendency to coalesce. This phenomenon occurs when two bubbles bump into one another and form a large bubble. This process can rapidly repeat, especially if there is a flooded effect on the stone surface. On a macroscopic level, coalescence leads to large bubbles that float through the liquid and escape at the surface. This process can be seen when boiling water in a pot. Very small steam bubbles adhering to the bottom of the pot gather with other small bubbles to form larger bubbles and the steam bubble rises through the pot and creates turbulence as the bubbles rise and burst at the surface. So what is the big deal with coalescence?
The purpose of wort oxygenation is to dissolve oxygen into wort. If small oxygen bubbles coalesce and rise to the surface of your fermenter, this means that the gas transfer process is inefficient. Although the inefficiency is not going to break the bank, it does make process control difficult because you don’t know how much gas dissolves into the wort unless you have a dissolved oxygen meter laying around. This brings up a fundamental question; how much oxygen is needed? I will skip the subject of determining what works best for a given beer type, yeast strain, or fermentation method and use an easy to manipulate target of 10 ppm (10 mg/l) oxygen. This is right in the middle of the range typically used in breweries.
To make this easy I will use a nominal batch size of 20 liters (about 5 gallons) to determine the amount of oxygen that is desired in the wort following oxygenation; and that amount is 20 liters x 10 mg/liter or 200 mg (0.2 grams). The molecular weight of oxygen is 32 grams per mole, so 0.2 grams is equal to 0.00625 moles. One mole of an “ideal gas” occupies 22.4 liters (at standard temperature and pressure), and this tells us that 0.00625 moles is equivalent to about 0.14 liters. So the target total volume of oxygen dissolved in this 20-liter wort volume is 0.14 liters or 140 milliliters (or 7 mL of oxygen per liter of wort). To scale up based on volume just multiply 7 mL/L by wort volume, or to scale up by desired oxygen content, scale up from 10 ppm.
OK, so here is the major assumption in this discussion: All of the oxygen that flows through your gas regulator and into the wort actually dissolves into the wort. This is the really nice thing about oxygenating with oxygen as opposed to aerating with air. Air contains about 79% nitrogen and you will always have undissolved nitrogen bubbles escaping wort, making it difficult to determine what is happening with the oxygen. When using oxygen you don’t want to see bubbles making it to the top of the fermenter. This is hard to do with wort, but you can tune your system with water. Remember, coalescence is not the idea and the desired result is a slow flow of small bubbles leaving your stone that disappear before rising to the surface. The truth of the matter is that there will be some loss in this process, but not much if the bubbles are very small.
So let’s return to the control of this process. The target is 140 mL of oxygen in your 20 liter batch, and you have a regulator with flow controller that is able to be dialed back to 16 mL/min. If you set this at 20 mL/min. and run for 7 minutes you will have the dose required. Add in some inefficiency and your target oxygenation time is somewhere in the 8-10 minute range. Like everything in brewing, you need to dial this in based on what actually works for your process. I hope this information is useful!
