We all know that making beer can be a complicated process, or it can be a simple one. It all depends on how involved you want to get. The more involved you get, the more control you can have over the end results. So every time I whip up a batch of beer, I try to learn something new to help give me more control of the outcome of my beer. This batch my focus was priming and carbonation. Let me share.

Priming is the addition of sugar to fermented beer immediately prior to bottling or kegging. The added sugar ferments in the sealed package, creating the carbonation for the beer. Sounds simple, right?

Most of the recipes I started with would tell me to add 3/4 cup priming sugar per 5 gallons at bottling time. Not surprisingly, the results always varied. Other recipes would say to add 1 1/2 tbsp priming sugar per bottle. Again, results varied. These methods are based on a volume per volume basis. Measuring this way can lead to different results. When you consider that not all sugars are not manufactured the same way or that 3/4 cup of packed sugar is not the same as 3/4 cup lose sugar, you’ll realize that measuring this way is not ideal. What makes more sense is to measure your sugar on a basis of weight sugar per volume beer. So now that we’re going to measure our sugar by weight, we need to know how much sugar to use.

------------------------------------------- Beer style Volumes CO_{2}------------------------------------------- British-style ales 1.5 - 2.0 Porter, stout 1.7 - 2.3 Belgian ales 1.9 - 2.4 European lagers 2.2 - 2.7 American ales & lagers 2.2 - 2.7 Lambic 2.4 - 2.8 Fruit lambic 3.0 - 4.5 German wheat beer 3.3 - 4.5 -------------------------------------------

Above is a handy guide to carbonation levels in a range of styles.

Before continuing on with measuring sugar, lets talk a little about carbonation. During fermentation, the yeast converts the sugars in the wort into alcohol and carbon dioxide. What this means is that when your beer is done fermenting, it already contains small amount of disolved CO_{2}. How much carbon dioxide is in the beer already is dependent on the beers temperature during fermentation. The lower the temperature, the more carbon dioxide can be dissolved into the beer. Because we are trying to determine how much sugar to add to acquire our desired CO_{2} levels, we need to know how much carbonation to add. How much carbonation we need to add is actually the target CO_{2} level minus the amount of CO_{2} left in the beer from fermentation. Below is a table of carbonation levels at various temperatures before priming.

Temp Temp | Temp Temp (degC) (degF) Vol.CO_{2}| (degC) (degF) Vol. CO_{2}------ ------ -------- | ------ ------ -------- 0 32 1.7 | 12 54 1.12 2 36 1.6 | 14 57 1.05 4 40 1.5 | 16 61 0.99 6 43 1.4 | 18 64 0.93 8 46 1.3 | 20 68 0.88 10 50 1.2 | 22 72 0.83

This would be a good point to find out exactly how much sugar it actually takes to produce 1 volume of CO_{2} per gallon of beer. After all, how can you find out how much sugar to add to your 5 gallons of beer without knowing the conversion rate of sugar to CO_{2}? A very simplified way of showing that conversion rate is written as follows:

C_{6}H_{2}O_{6} + yeast = 2CH_{3}CH_{2}OH + 2CO_{2}

Now, you don’t need to know how all that works. Only that it means that yeast will convert one unit of glucose into two units of ethanol and two units of carbon dioxide. So if we want one unit of CO_{2} we would use 1/2 unit of glucose, or .49 oz glucose per one gallon off beer. So if we wanted to add 1 volume of CO_{2} to 1 gallons of beer, we would need 1 (vol CO_{2}) x .49 (oz glucose) = .49 oz of glucose. Still following?

So what if we wanted 2 volumes of CO_{2} in a gallon of beer? We would need 2 x .49 = .98 ox of glucose. And 3 volumes of CO_{2}? 3 x .49 = 1.47 oz glucose. Are you sensing a pattern?

Let’s think back about what we are doing. We want to know how much sugar to add to our beer to achieve the level of carbonation that we want. We’ve determined what our target CO_{2} level should be using the handy CO_{2} level guide above. We know that a certain amount of CO_{2} dissolves in the beer during fermentation, which we’ll have to subtract from our target CO_{2} level. We also know that it takes .49 oz of glucose to produce 1 volume of CO_{2} in one gallon of beer. Using this information and the formula above, we can create a precise formula for finding the amount of sugar/glucose needed to achieve the desired levels of CO_{2} in your beer.

Using the chart above, find the saturation level for the temperature of your beer. Let’s call that V_{0}. Then choose the CO_{2} level that corresponds with the style of beer you are making. Let’s call that V. Now we can subtract the two and add it to the formula from above.

Priming rate (oz/gal) =

(V-V_{0}) x .49

or for the non-oz version

Priming rate (g/L) =

(V-V_{0}) x 3.7

Then all you have to do is multiply that by how many gallons of beer you have. So let’s say we are going to make 5 gallons of Belgian Ale that fermented at 50?F. Our target CO_{2} volume level will be 2.1 vol (V). From the above table we know that 1.2 vol (V_{0}) of CO_{2} has been dissolved in the beer during fermentation. Therefore:

(2.1 – 1.2) x .49 = .441 oz glucose/gallon

Multiply that by our 5 gallons of beer and you get 2.2 oz of glucose that you would need to add to your Belgian ale to get your target CO_{2} level of 2.1.

Carbonation levels in a beer can tell you quite a bit about a beer. It can also tell you quite a bit about a brewer. The beer style chart at the beginning of this article is a relatively short list. It is also relative. As home brewers, we have the capability to adjust the CO_{2} levels to appease our own palette. Knowing how to reach the carbonation level that you want for your beer brings you one step closer to making a beer that is truly your own.

I still say that mathematical skills are a form of mental illness, but I think you’ve really found a way to make it work for you. 🙂