How to Measure and Understand Alcohol Contents in Beer
Consumable alcohol –more correctly known as ethyl alcohol– is a natural by-product of the fermentation process. When yeast eats liquefied sugars (called maltose in beer), it excretes alcohol and carbon dioxide as waste products. How much alcohol and carbon dioxide is excreted is directly related to how much sugar is available for the yeast to eat.
You can brew your own beer and home and not ever care about its alcohol content, but you’d be in the minority. Most homebrewers are very interested in knowing the alcohol content of their beer, and, in fact, many design their homebrew recipes to target specific alcohol levels. For the average homebrewer, the cheapest and most effective way to figure this out is with a hydrometer.
ABV versus ABW
There are two ways to express alcohol content in beer. Both are scientifically accurate, but one can be somewhat misleading when compared to the other. What we’re talking about here is the listing of alcohol by volume and alcohol by weight.
The more common method of listing alcohol content in beer is by actual percentage of volume, which is the law in the U.K. and Europe. In the U.S., it’s customary for some corporate brewers to list the alcohol by weight.
Hydrometers used by homebrewers always register alcohol by volume, and they say so right on the paper insert.
By standard measure, a pint of water weighs 1 pound (actually a fraction of an ounce over). A pint of alcohol, on the other hand, weighs only .79 of a pound. Because alcohol weighs less than water (and beer, and most other liquids), the weight of alcohol appears to be lower in weight when comparative measurements are made.
To make the point clearer, imagine the container of beer as a carton of 10 masonry bricks. If you take out 1 brick and fill the open space with a foam block of equal size, the foam block still takes up 10 percent of the space in the carton, but it weighs considerably less than the brick it replaced.
So, a beer with an alcohol content of 3.2 percent by weight actually contains 4.05 percent by volume; a beer that is 4 percent alcohol by weight actually contains 5 percent by volume. To figure it out yourself, convert an ABW reading to an ABV by multiplying the ABW by 1.25. To convert an ABV reading to ABW, multiply the ABV by 0.79.
Just remember that figures for weight are lower than those for volume.
Non-Alcoholic Hombrew Is N/A (Not Achievable)
Brewers who want to produce a non-alcoholic brew at home are going to be sorely disappointed. As mentioned above, yeast is not only the catalyst for fermentation, it adds all kinds of aromas and flavors to beer and can have a major influence on the beer’s texture and mouthfeel. Therefore, just not adding yeast to the beer in not a viable solution to making non-alcoholic beer. Unfermented beer is very thick, sweet, and not at all thirst-quenching.
Commercial brewers are able to produce non-alcoholic beers in a number of ways, all of which require equipment and technology far beyond the resources of homebrewers. The old-fashioned methods involve reboiling already fermented beer. Because alcohol boils at lower temperatures than most liquids, it evaporates quickly from the beer. After the boiling is done, however, the beer is flat (because it was the yeast that put the carbonation in the beer in the first place) and must be artificially pumped full of carbon dioxide. A second, more modern method involves pumping the fermented beer past thin membranes that remove the alcohol by osmosis.
The bottom line: it’s cheaper and easier to buy non-alcoholic beer from your local retailer.