Calculating Sugar Additions for Carbonation
Joining a few friends for a nice cold beer with a bright frothy head is a time- honored tradition, here in the US and around the world. In fact the carbonation, foam, and bubbles are critical to the appearance, flavor and appeal of beer. Any serious brewer or beer aficionado knows when a beer is properly carbonated. It has the perfect appearance, right flavor and the correct mouthfeel. Under-carbonated beers look and taste flat, and can be unappealing to drink. Over-carbonated beers gush from the bottle or tap, instantly filling the glass with foam, and for many styles can be as unappealing as flat beer.
Most people know that carbonation comes from carbon dioxide (CO2) dissolved in the beer, just as CO2 is injected in your soda to give it carbonation. CO2 gas is an interesting compound, as it interacts with the “trigeminal” senses in your mouth. Trigeminal senses are a combination of pressure, position, and pain. These are the same receptors that detect painful chemical irritants in your mouth, so they produce a complex feeling of both pleasure and pain — enhancing the mouthfeel, body, aroma, and flavor of the beer.
The History of Carbonation
There is general agreement that beer was uncarbonated or very lightly carbonated for most of its 4,000+ year history. To produce carbonated beer, you need a pressure vessel of some kind such as a bottle or tightly sealed keg. While some cask-aged beer likely had light carbonation, much like a modern real ale, beer was not carbonated as it is today.
Carbonated beer is closely tied to the introduction of bottling. The first bottled beer goes back 440 years in Hertfordshire, England. A forgetful rector named Dr. Alexander Nowell filled a bottle with beer, left it by a river bank and found it later to be well carbonated (recorded in Thomas Fuller’s History of the Worthies of Britain). Reportedly, “he found no bottle, but a gun, such was the sound at the opening thereof; and this is believed the original of bottled ale in England.”
Whether Fuller’s tale is true or not, bottled beer was still not widely available until much later. Some brewers experimented with bottling in the 1600s but the glass at the time was thin, weak and expensive. In the 1700s and through to the early 1800s commercial brewers started producing bottled beers, primarily for export markets. Glass was still expensive, but they were often able to sell both the beer and the used bottle on the export market at a profit. Bottles were still blown, filled, and corked by hand, and the long trip and unattenuated fermentation often led to high carbonation rates.
Not until the late 1800s did we see large-scale bottle production and bottling operations. Whitbread in London launched one of the first large -scale bottling operations in 1870, though the bottles were still hand corked. The screw top bottle was invented in 1879 by Englishman Henry Barrett, and Louis Pasteur’s invention of “pasteurization” to preserve beer in the 1870s paved the way for modern distribution and long term storage of bottled beer. The addition of refrigeration also made it possible to serve highly carbonated kegged beer, as well as allowed lagers to be fermented and produced year round.
Measuring Carbonation
As I mentioned earlier, carbonation is simple CO2 gas dissolved in the finished beer. Most homebrewers measure the carbonation level in “volumes.” One volume of CO2 is simply the amount of CO2 gas dissolved in the same amount of liquid at 20 °C (68 °F), at atmospheric pressure. So you can think of a liter of CO2 dissolved in a liter of beer as being one volume. Two volumes would be two liters of CO2 dissolved in one liter of beer.
Carbonation rates for different beer styles vary widely. An English cask ale might have only 0.75–1.3 volumes and be flat by American standards, while a typical American lager would be in the 2.6-2.8 volume range. A highly carbonated Bavarian wheat beer could be in the 3.6–4.4 volume range, but is actually poured in several stages to prevent it from foaming over the glass. These are some extremes, but in general most US beers are served in the 2.4–2.9 volume range.
Another popular measure used by many professional brewers and researchers is grams of CO2 per liter of beer. If you do the math, you will find that approximately 2 grams/liter is 1 volume of CO2, so you can get a good approximation by taking the number of volumes and doubling it. If you want to be more precise, one volume is 1.926 grams/liter of CO2.
Carbonation and Fermentation
There are two ways to carbonate your beer. The first is forced carbonation, which is done with many commercial beers, and also by homebrewers using kegs. In forced carbonation, the beer is put in a keg or other pressure vessel or line and then CO2 gas is added under pressure. This forces the CO2 to dissolve into the beer, typically carbonating it within a few days.
The second method, which we will cover in more detail here, is natural carbonation. For natural carbonation a sugar or other fermentable is added to the beer when it is bottled or kegged, and then sealed. The yeast remaining in the beer consumes the sugars, producing CO2 as a byproduct. This CO2 provides carbonation in the sealed bottle or keg. The key is getting the right level of sugars to achieve the desired carbonation level, and also making sure you still have some healthy yeast in the beer.
Calculating Carbonation Sugar Needed
Start by calculating the weight of corn sugar needed to bottle 5 gallons (19 L) of beer. It’s important to calculate the weight, as sugars have varying densities depending on how they are milled. Though you may find recipes that say “add 2⁄3 cup of sugar” in the instructions, measuring bottling sugar by volume is not recommended — always weigh your sugar.
The following formula is for corn sugar (dextrose), but you will see that you can scale the result to calculate the weight needed for dried malt extract (DME), honey, and other fermentables used for priming.
Weight_oz = (0.5360 * Vol_gals) * ((Vols_desired – 3.0378) + (0.050 * Temp_f) – (0.0002655 * Temp_f * Temp_f))
Where:
Weight_oz = Weight of corn sugar to use when bottling
Vol_gals = The volume of the beer to be bottled in gallons
Vols_desired = The number of volumes of CO2 you want in the finished beer
Temp_f = Temperature of the beer at bottling in degrees Fahrenheit
Note that the temperature of the beer at bottling is important as it determines how much residual CO2
is in the beer from the main fermentation. The residual car-bonation after fermentation is based on the temperature and Henry’s Law. Let’s calculate the amount of corn sugar needed for a 5-gallon (19-L) batch of beer that is sitting at 68 °F (20 °C) that we want to carbonate to 2.8 Volumes of CO2:
Weight_oz = (0.5360 * 5) * ((2.8 – 3.0378) + (0.05 * 68) – (0.0002655 * 68 * 68)) = 5.1858
So the Weight_oz = 5.2 oz. In this example we would need to use 5.2 oz. of corn sugar (dextrose) by weight to achieve 2.8 volumes of CO2 in our 5-gallon (19-L) batch of beer.
For those working in metric the equivalent calculation using temperature in centigrade, and volume in liters works as follows: First calculate the temperature of your beer at bottling in Fahrenheit (from Celsius):
Temp_f = (9*Temp_C/5 ) + 32
Next calculate the weight of corn sugar needed in grams:
Weight_grams = 4.01 * Vol_liters * (Vols_desired – 3.0378 + 0.050 * Temp_f -0.0002655 * Temp_f * Temp_f)
A spreadsheet, online carbonation calculators, or beer brewing software like BeerSmith, ProMash, or Beer Tools, can also calculate this for you.
Using Sugars Other than Corn Sugar
You don’t have to use corn sugar for carbonation. You can use just about any fermentable to carbonate your beer. Popular options include dried malt extract (DME), table (white cane) sugar, and honey. Each of these pro-vide the sugar needed for carbonation, but each is fermentable to a different degree. For example, DME provides about 65% of the priming effective-ness of corn sugar, so you would need to use 1.0/0.65 = 1.54 or 54% more DME than corn sugar to prime the beer. The table on the top right of this page shows some popular options. To use the table, start with the corn sugar calculation covered earlier and multiply the weight by the percentage shown in the third column. Using the example from earlier (5 gallons of 68 °F beer carbonated to 2.8 volumes) we calculated 5.2 oz. of corn sugar was needed. If we want to use honey at bottling, we take the 110.5% number and multiply it by 5.2 oz. to get: 5.74 oz. of honey. So we would use 5.74 oz. of honey to carbonate our batch of beer. Note, however, that honey takes much longer to ferment and carbonate than other sugars.
Priming and Carbonating Bottles
Once you have calculated the amount of sugar for bottling, you can prime and bottle the beer. I recommend transferring your beer from its fermenter into a bottling bucket, and then mixing the priming sugar in gently. This will give you a consistent carbonation level across the batch of beer and is much simpler than trying to measure a few grams of sugar to add to each bottle individually. You can also use priming tablets in your bottles if you don’t want to measure the priming sugar (which is great if you are bottling a small batch of homebrew). Priming tablets are single, measured doses of priming sugar that are added one to a bottle.
When bottling, it is customary to leave about an inch to inch and a half (2.5-3 cm) of headspace at the top of the bottle. The headspace provides a bit of oxygen for fermentation, but more importantly provides some relief for pressure in case the bottle becomes overly carbonated.
Once all of the bottles are filled and capped, store them at fermentation temperature for a week or two (more for honey) to allow the yeast to carbonate the beer. If you are planning to cold crash your beer to aid in clearing it, open one bottle and make sure it is properly carbonated before refrigerating the bottles.
Head Retention
It is important to know that beer does not spontaneously foam. It requires some energy or a trigger to release CO2 using a process caused nucleation. Nucleation is the same process that occurs when you drop a Mentos candy into a Diet Coke.
A rough surface or scratches in the glass is sufficient to release CO2. Some glasses are even specially designed with scratches in the bottom to serve as nucleation sites, and provide a steady stream of bubbles to maintain the head. In fact, the widget at the bottom of a Guinness can is actually a nucleation device and not a CO2 or nitrogen cartridge as some people believe. It serves to release the carbonation (mainly nitrogen), but does not add to it.
Temperature also induces foam; higher temperature forces more gas from the beer. Hot beer foams more than cold beer, and more CO2 is released as your beer warms in the glass.
The foam at the top of your beer, called the head, is actually another complex chemical structure. Surface tension on the boundary between beer and air is constantly acting to break bubbles and release CO2. However, beer has surface acting materials that hold the bubbles together and fight the surface tension.
Proteins and bitter acids are the two main components that are hydrophobic (water hating) that stick together and hold the head of the beer together. Otherwise it would collapse quickly. Proteins are derived from your malt bill, and bitter acids come from hops. Both work together to give you a creamy long lasting head.
There are also a number of foam negative materials that can be present. These include soap and detergents often used to wash glassware, as well as fats and lipids from greasy plates, foods, or even your lips or moustache that can break down the foam in your beer. Wash glassware separately from regular dishes and not using regular detergent or dish soap.
Improving Head Retention
Here are a couple of ways to improve the head retention of your homebrew:
• Use body and head enhancing malts. Malts that are high in proteins and dextrins such as crystal/caramel malts, wheats, “cara” malts, flaked grains, and oats will enhance the head retention of your homebrew. Dark malts have melanoidins that also aid in foam stability. However, you do need to manage the protein content as it can also contribute to clarity problems in lighter colored beers.
• Adjust your mashing schedule. Steps that break down large proteins such as a protein rest can be detrimental.
Also mashing at the higher end of the temperature range of 154–158 °F (68–70 °C) will leave more unfermentable sugars, enhancing body and head retention. A low mash pH (in the 5.2 range) can also aid in head retention.
• Use more hops. The bittering acids in hops are also hydrophobic, so a beer with more bittering units will have better head retention. This is why IPAs often have great head retention.
• Don’t use household soaps on drinking glassware and brewing equipment. Also don’t wash your glassware with regular dishes.
• Choose the right glass. Yes, the shape of the glass can drive both head formation and head retention. A narrow glass such as those used to serve Pilsners enhances the formation of the head, while short wide glasses do not. Tulip glasses also retain the head and aroma of the finished beer.
Prime Properly
Next time you enjoy a naturally carbonated beer with a perfect head, think about all of the amazing bits of chemistry that came together to create that white foam. Carbon dioxide, proteins, bittering acids, and melanoidins fighting off the surface tension of the beer itself; a priming agent carefully selected and measured to get just the right carbonation level. All poured into the right glass at the right time for you to enjoy!
