March 29, 2018
Fermented beverages have been around since ancient times, as fermentation is a practice that has been used by humans for thousands of years. While it has been used for preserving food and beverages, fermentation has arguably been used more commonly for the creation of alcoholic beverages such as beer, spirits, and wine. Beer is a popular option, as annual production in U.S. is in the hundreds of millions of barrels.
Over the last decade, the popularity of craft brews has led to a tremendous boom in the number of smaller microbrewing operations across the U.S., and recently small craft distilleries have also begun to emerge. There is a large variety in flavors, styles, and crafting techniques across the nation. However, the testing techniques to determine alcohol content for all alcoholic beverages is largely the same, and accurate ABV content must be reported to government agencies as part of regulatory standards. It is imperative to understand the use of these methods as a craft brewer or distiller, especially when creating products for consumer use. All of these methods are used when measuring the specific gravity of an alcoholic beverage, which is required for the computation of ABV.
Specific Gravity
Specific gravity is the ratio of the density of the beverage compared to the density of a standard solution. In the context of fermenting alcoholic beverages, it refers to the specific gravity, or relative density of the wort or must at different stages in the fermenting process compared to water. It can be measured through the use of a few different instruments, but two of the most common instruments are the alcoholmeter or hydrometer.
Alcoholmeter
This is the ideal tool to use when measuring the amount of alcohol in distilled spirits, and only in a pure distilled spirits. This particular instrument is calibrated to the density of pure ethanol, therefore the presence of sugars or other soluble substances can affect the readings. While an alcoholmeter and a hydrometer may look similar and be used in similar methods, they are calibrated differently and cannot be used interchangeably.
Hydrometer
Unlike the alcoholmeter, the hydrometer is calibrated to the density of water. In less technical terms, this means that it can be used on beverages both before and after fermentation. A reading from a hydrometer will give you the potential alcohol content. Since sugar content can effect results, specific gravity readings should be taken before and after the fermentation process. The approximate alcohol content is then determined by subtracting the post-fermentation gravity from the pre-fermentation gravity.
Something to consider with the above instruments:
The temperature of the beverage can effect the reading. It is important to follow the instructions of the instrument being used. In most cases readings should be taken at 68°F (20°C).
