Properly Priming Your Homebrew
For many people today, soda is the first beverage that comes to mind when thinking of carbonation. Yet it may well be that the first such beverage was beer. That’s because evidence suggests the early brewers, the Mesopotamians and later Egyptians, often drank their brews while they were still fermenting. Indeed, back in the Middle Ages when hops were not used in Britain the ale was often drunk before fermentation was complete, and a similar situation probably applied in the rest of Northern Europe. In part that was because such ales did not keep well and would quickly sour. When hops were first used in beer their advantage lay not just in taste but in their preservative effect, so that beer could be kept drinkable much longer. As a matter of fact, we now know that the presence of CO2 helps to preserve beer somewhat by limiting the presence of oxygen, the arch enemy of fresh beer.
The notion that beer should always be carbonated took a while to catch on; since it was often the practice to let stronger beers mature in wooden casks for a year or more. During that time most of the residual CO2 would escape and the beer would be drunk flat. That began to change in Britain in the 18th century as drinkers demanded that their beer should be drunk while fresh, or “running” rather than after long aging. Of course in Germany the discovery of bottom fermenting yeasts and the development of lagering at cold temperatures resulted in well-carbonated beers. Also, carbonating wines by priming with sugar for a secondary fermentation had been around since some time in the 16th century, and put onto a firm footing by the French monk Dom Perignon who invented a suitable closure for this wine that we call Champagne.
Carbon dioxide was discovered by a Scot, Joseph Black, in 1754. In the early 1770s Joseph Priestley made a study of what was then known as “fixed air.” Fittingly, this was in a brewery in Leeds, Yorkshire, where, among other properties of the gas he found that he could produce a pleasant, fizzy drink by dissolving it in water, and soon “soda water” became a fashionable drink in Europe. For the record, Priestley discovered no less than ten gases, including oxygen. He was a religious dissenter and supporter of the French Revolution, opinions that eventually forced him to flee to America, where he lived until his death in 1804.
But this article is supposed to be about carbonating your beer to the correct level. How you do this depends upon whether you are bottling or kegging, and I’ll talk about those separately. First, you need to know how much CO2 you want your finished beer to contain. This is measured in “volumes of CO2,” or the volume the CO2 in the beer would occupy (at standard temperature and pressure of 0 °C, 760 mm mercury) per volume of beer. Don’t worry that your beer is not at this temperature and pressure, this is just the way in which it is measured. Just remember that as a recent case with certain NFL footballs showed, a lot of people do not understand the relationship between gas pressure and temperature!
The level of CO2 does affect the taste of the beer, since it can impart some fullness to beers that might
otherwise taste a little thin, such as pale lagers. At high levels the gas can break out of the beer when in your mouth and the resultant acidic “prickle” may or may not be desirable in a particular beer style. Too much conditioning in a beer that is meant to be malt-accented, such as a brown porter, will mask some of
the malt character. On the other hand, hop flavor will be accentuated by higher carbonation levels, so it is an important consideration in getting your IPA just right. It is also an important factor (though not the only one) in getting the right head on your beer so that it looks like it should when poured. Therefore, there are different levels of CO2 that are appropriate for different beer styles.
Beer Style CO2 Volumes
American ales 2.2–3.0
British ales 1.5–2.2
German weizens 2.8–5.1
Belgian ales 2.0–4.5
European lagers 2.4–2.6
American lagers 2.5–2.8
The underlying assumption here is that you are serving the beer at the correct temperature, usually 40–45 °F
(4.5-7.2 °C), and remember that the solubility of the gas decreases with increasing temperature. If for some odd reason the beer is much warmer than that you may find you get nothing but foam when you pour it! Also note that the figure for “British Ales” applies to bottled and kegged ales, and is somewhat high for cask-conditioned ales, which I shall deal with later.
Priming for Bottling
Many writers (including me on occasion) have recommended that you add a standard amount of priming sugar when bottling, usually something like 3–5 ounces corn sugar, or 2⁄3 to 3⁄4 of a cup. That, however, is a dangerous over-simplification, for no matter how flat your beer looks and tastes after fermentation is over, it still contains some dissolved CO2. Just how much will depend mainly upon the temperature of your fermentation, and is practically impossible for the homebrewer to measure. But there’s no need to despair, because there are plenty of sources that will give you a close approximation. Prime (no joke meant) among these is BYO’s Carbonation Priming Chart, but a couple of other sources, Northernbrewer.com and Tastybrew.com both give calculators that will work this out for you. I won’t repeat those numbers here, but using them is simple. Let’s say you were brewing a British-style bitter, and fermented it at 65 °F (18 °C) then BYO’s chart gives it a CO2 content of 0.894 volumes; from the table above you would be aiming for 1.5–2.2 volumes CO2 in the beer after conditioning. So, through priming you need to add 0.6–1.3 volumes of the gas. But just bear in mind that these numbers do not allow for the beer that has sat around for some time at temperatures higher than that for the fermentation, and make adjustments to these numbers if that is the case.
But, how do you work out how much sugar you need to get that extra gas into your beer? Well, that depends on what you are priming with since corn sugar (glucose) comes either in the anhydrous or in a hydrated form. The former will give slightly more CO2 for a given weight than the latter (actually 1 g of each gives 0.49 g and 0.44 g CO2 respectively). You will see from the BYO chart that this means that 1 oz. (28 g) of glucose in 5 gallons (19 L) gives 0.37 volumes CO2 while 1 oz. (28 g) of glucose monohydrate in the same volume gives 0.34 volumes of the gas. You might prefer to use cane sugar, as I do; this is very pure sucrose and 1 oz. (28 g) of this in 5 gallons (19 L) will yield 0.39 volumes CO2.
So, getting back to your bitter, let’s say you don’t want it too highly carbonated and are going for the bottom end of the range, 1.5 volumes CO2, which as we saw earlier means you need to add 0.6 volumes from your priming sugar. You can either read the required amount off the BYO chart, or simply calculate it from the figures in the previous paragraph. Glucose requires 0.6/.37 = 1.6 oz. (45 g.); glucose monohydrate 0.6/0.34 = 1.8 oz. (51 g.); sucrose needs 0.6/0.39 = 1.5 oz. (43 g.).
You can add the sugar directly to your beer and hope you do not create concentration zones where the sugar level is too high for the yeast to handle, but it is best to add it as a solution first. Just dissolve the sugar in, say, a cup of water, boil, and cool under tight cover before adding it to the beer. Note that you should be weighing the sugar on a suitable scale — if you have gone through the exercise of calculating it out exactly you should weigh the sugar exactly. And, of course, you need to have a healthy yeast in your green beer to ensure that this sugar is actually fully fermented. Ideally, a fresh yeast sample should be used at bottling, but that isn’t very practical for the homebrewer, partly because if not done very carefully it can result in an undesirable yeast residue in the bottle.
There is another technique for “priming” and that is kräusening the beer — adding a portion of fermenting wort just as it comes into head formation (kräusen). You would need this addition to be a wort of similar character to the beer you are making, and would have to calculate not only how much sugar you need, but also how much sugar is in the wort. There is also a risk of forming too much residue in the bottle — when large breweries use this technique they are able to remove the yeast formed, while maintaining the required carbonation level. So, I think it is more practical for the homebrewer to stick to the simple approach of adding sugar directly.
Priming for Kegging
You can do this exactly as if you were bottling, following the approach outlined earlier. But, of course, there is a simpler way, and that is to force carbonate the beer by applying pressure from your CO2 cylinder. First you have to decide how many volumes of CO2 you want in the beer and at what temperature you are going to serve it. Bear in mind that if you keep all your kegs in one freezer and you have different styles in them, your serving temperature may differ from the “ideal” for a particular beer styles (or you may have your own ideas as to how you want to serve your beer!).
Online carbonation charts list gauge pressure and serving temperature on the axes and volumes of CO2 in the body of the chart. It may look complicated at first glance, but it is easy enough to use. Let’s take the English bitter again, and assume that now we want to serve it at 50 °F (10 °C) and at a slightly higher carbonation level of 1.9-2 volumes CO2. Just go down the left hand column to 50 °F (10 °C), then across to 1.9 and 1.98 and up to the top row read off the required applied pressure, which will be 10-11 psig. Connect to your gas cylinder, set the gauge to this level, open the valve and you will be able to serve your beer exactly as you wanted.
Or will you? Well, no actually, because it takes some time, perhaps weeks before the beer and gas come into equilibrium. Various brewers have various solutions to this. For example, I tend to want lower carbonation levels than many American brewers prefer (remember, I did start my drinking career in Britain). That means I am happy to leave the beer at target pressure for two or three weeks before drinking it. A trick favored by many is to apply a higher pressure than targeted (say 30 psig) and to shake the keg vigorously, or even roll it, over a matter of two or three days, then drop the pressure to your target value. Some like to just set gauge pressure to 30 psi for a couple of days, then drop to 15 psig for another two or three days and finally to adjust it to target. Or, a more repeatable method is to set the pressure at about 4 pounds higher than the target for about a week and then reduce the pressure to the target. This reduces the maximum deviation from the target to about 2-3 pounds since it takes a very long time to reach equilibrium with this method.
Cask-Conditioned Ale
Traditionally, English ales are ideally primed and conditioned in the cask from which they are served. Although it is not so common in England as it once was, still quite a few pubs serve their beer this way. It should not be “warm” as too many Americans think, but at cellar temperature, which in England is commonly around 50–55 °F (10–13°C). Bitter, for example, as a low gravity beer (3.5-5% ABV) with distinct estery flavor notes will taste bland if served at 40 °F (4.4 °C). Its flavor can also be killed by over-carbonation, and it should not be more than 1.5 volumes CO2, (which means priming with as little as 1–1.5 oz./28–42 g glucose to 5 gallons/19 L). The conditioning fermentation takes place in the cask, some of the gas being allowed to escape through a porous peg in the bung hole. When fermentation subsides a hard peg is inserted in the bung; this is removed when the beer is drawn off, and replaced in the intervals between serving. This means, depending upon the skill of the server, the beer will lose condition during its life in the cask, and may often be served at as little as 1 volume CO2. That’s why the myth that English beer is flat has established itself, but as I explained earlier that does not mean that it has no carbonation. It is true that it sometimes has no head when drawn off by a hand pump on the bar. That is only true if there is no restriction on the outlet of the pump, as always used to be the case in southern England. However, nowadays it is more common for pubs to use a sparkler at the end of the “goose neck” outlet. This little device simply screws onto the end of the outlet and has a number of small holes around its circumference; when the pump forces the beer through these restrictions the beer will be delivered into the glass with a head. But that is really mechanical head formation, rather than just CO2 break out.
