As you begin experimenting with making your own liqueurs, you’ll invariably run up against the “what percentage of alcohol is this?” question. It can be tricky. You can measure the amount of alcohol in a pure base spirit by measuring its specific gravity. This is done with a hydrometer (found in all home brewing supply shops). Once a spirit is diluted with anything besides distilled water, the reading will lose accuracy – all bets are off. You can no longer use a hydrometer to measure the concentration if you’ve added any sugar, or any other soluble substance to your base spirit. It won’t be anywhere close to accurate.
In calculating the alcohol content of your creation, you must always begin with the alcohol content (by volume) of the base ingredients. If you don’t have that, you will not be able to compute your alcohol content. Sure, you could take a stab in the dark by liqhting your creation (a concentration will sustain a flame right around 40% ABV) but why resort to something of questionable safety (or worse, consume some of the alcohol of your precious hard work)?
Proof versus Alcohol By VolumeFirst, let’s get some definitions here. “Proof” is the concentration of alcohol in an alcoholic beverage. This traditional term reportedly arose from “proving” the alcohol concentration of rum rations in the British Navy. It has a mathematically direct relationship with alcohol percentage by volume. Proof is twice the percentage of alcohol (by volume). Thus, 80 proof vodka contains 40% alcohol by volume. The maximum possible proof of beverage grade ethanol is right around 196. Any higher concentrations aren’t considered beverage grade, and usually absorb moisture from the air, bringing their concentration back down.
Typical alcohol concentrations
In calculating our alcohol content, we always begin with our base ingredients. I often start with a neutral grain spirit at 190 proof (95% alcohol by volume). Here are some typical concentrations:
Vodka, Gin, Whiskeys: 38% – 45% ABV (76 – 90 proof)
Brandy: 40% ABV (80 proof)
Vermouth (fortified wines): 17-23% ABV (35 – 46 proof)
151 Rum: 75% ABV (151 proof)
Grain alcohol: 75% – 96% ABV (151 – 192 proof)
When creating your liqueur, the first thing to do is to determine the actual amount of ethanol in your base spirits. Take the volume of the spirit in liquid measure (fluid oz, cups, ml) and multiply it by the percentage of alcohol by volume. Divide that amount by 100. That will be the liquid measure of ethanol in your base.
(Total Volume X Percentage of Alcohol) divided by 100
For example: Let’s say we’re creating an amaro that begins with 2 cups (16 oz) of grain alcohol at 75% ABV
1) Multiply alcohol volume by its ABV concentration:
16 X 75 = 1200
2) Divide the product by 100:
1200 ÷ 100 = 12
There are 12 oz. of ethanol in our 2 cups of grain alcohol at 75% ABV.
This is the alcohol liquid measure that will (more or less) remain constant for all of your concentration calcuations of this particular batch (assuming little evaporation).
Now, the alcohol percentage of your finished amaro, liqueur or spirit can be calculated by dividing the original alcohol liquid measure by the total volume of your finished spirit. If two cups of liquid (water, infusions, syrup) are added to the 2 cups of grain alcohol, the total spirit volume is, of course, 4 cups. The resulting spirit is now:
12 oz ethanol ÷ 32 oz (4 cups) = 37.5% ABV or 75 Proof
Note that this is completely different than comparing the specific gravity of wort and the finished beer to determine ABV. In that case, no additional liquid is added so the process is more or less isochoric (constant-volume).
How about adding different spirit components?
Determining alcohol content when adding different components isn’t much more difficult either. Let’s say you’re creating a liqueur by adding a cup of brandy at 80 proof, a cup of sweet vermouth at 34 proof, and a cup of grain alcohol at 151 proof. How do we calculate the combined concentration?
We begin by calculating the liquid measure of alcohol of each component separately:
1 cup (8 oz) of brandy at 80 proof
8 oz X 40% ABV = 320
320 ÷ 100 = 3.2
3.2 oz of alcohol in 1 cup of brandy
1 cup (8 oz) of sweet vermouth at 34 proof
8 oz X 17% ABV = 136
136 ÷ 100 = 1.36 or 1.4
1.4 oz of alcohol in 1 cup of vermouth
1 cup (8 oz) of grain alcohol at 151 proof
8 oz X 75% ABV = 600
600 ÷ 100 = 6
6 oz of alcohol in 1 cup of grain alcohol
Add the alcohol liquid measures together: 3.2 + 1.4 + 6 = 10.6 oz of alcohol
Add the total spirit volume: 3 X 8 oz = 24 oz.
Thus, the alcohol content of combining all three ingredients together: 10.6 oz alcohol ÷ 24 oz total volume = .441 or 3 cups at 44% ABV (88 proof).
Simple, isn’t it?
How to determine the amount of liquid to dilute a spirit to a desired concentration
This seems tricky at first, but it really isn’t. To find out how much liquid to add, begin by getting the alcohol content of the existing concentration. Using the example above, we have 10.6 fluid oz of alcohol in 3 cups. To find the amount to add, divide the alcohol liquid measure by the desired concentration (% ABV in decimal form) to get the new total spirit volume. Subtract the original total spirit volume and you’ll have the amount of liquid to add to bring it to a desired concentration.
In other words:
If we want to dilute the above example so that it’s final concentration is a 30% ABV,
1) Get the alcohol liquid measure of the solution as it is now:
2) Divide that by the desired concentration percentage:
10.60 ÷ 0.30 = 35.33 oz (total spirit volume)
3) Subtract our original volume:
35.33 – 24 = 11.33 oz.
We would need to add 11.3 oz of a non-alcoholic liquid to drop the concentration down to 30% ABV.
Equally simple, right?