In an earlier blog, Measuring the Alcohol Content in Wine, some of the general points are covered relative to the alcohol content of wines and the various methods for its measurement.
I use the potential alcohol method to measure the alcohol content in my wines. This method is simple and it gives acceptable results. First, I set up the area where I am going to do the measurement by bringing together in the same space the wine or must, the hydrometer, the transparent cylinder that I will use, and a thermometer. The cylinder will contain the wine or must and the hydrometer. These items are left for about three or four hours before making any measurements so that they are all at pretty much the same local temperature.
When I am ready to measure potential alcohol (see the video above), I place the hydrometer into the cylinder holding it by its upper tip. I add the wine/must to the cylinder until the hydrometer floats, give the hydrometer a spin to get rid of bubbles that might be adhering to the glass, and let it come to rest on its own. When the hydrometer stops moving and is floating freely not touching any part of the cylinder, I record the specific gravity reading.
As an example, for the rose' must, I measured its specific gravity on August 31, 2012 (using the hydrometer calibrated at 60oF) and got 1.106 at a temperature of 27oC (80.6oF). At this temperature the specific gravity requires a correction of 0.002 to be added to the reading giving 1.108 as the corrected specific gravity. According to the table of potential alcohol for this specific gravity reading a wine of 14.2% potential alcohol by volume should result. On August 9, 2013, almost one year later, I measured the specific gravity of the rose' wine that this must produced and got 0.992 at 28oC (82.4oF) which requires a correction of 0.003 giving 0.995 as the corrected specific gravity. But this reading is below 1.000 which indicates that all the sugars have been consumed and this is an essentially dry wine of 14.2% alcohol by volume. If this had not been the case, the latter potential alcohol reading would be subtracted from the former to get the alcohol content: 14.2% - 0% = 14.2%.
Potential alcohol tables are readily available on the internet along with detailed instructions for their use. Just use the search terms potential alcohol table and you will get a long list to choose from. In fact, the hydrometer that I use came packaged with instructions for its use along with a potential alcohol table and instructions for making temperature corrections to specific gravity readings.
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| Specific Gravity Materials |
As an example, for the rose' must, I measured its specific gravity on August 31, 2012 (using the hydrometer calibrated at 60oF) and got 1.106 at a temperature of 27oC (80.6oF). At this temperature the specific gravity requires a correction of 0.002 to be added to the reading giving 1.108 as the corrected specific gravity. According to the table of potential alcohol for this specific gravity reading a wine of 14.2% potential alcohol by volume should result. On August 9, 2013, almost one year later, I measured the specific gravity of the rose' wine that this must produced and got 0.992 at 28oC (82.4oF) which requires a correction of 0.003 giving 0.995 as the corrected specific gravity. But this reading is below 1.000 which indicates that all the sugars have been consumed and this is an essentially dry wine of 14.2% alcohol by volume. If this had not been the case, the latter potential alcohol reading would be subtracted from the former to get the alcohol content: 14.2% - 0% = 14.2%.
Potential alcohol tables are readily available on the internet along with detailed instructions for their use. Just use the search terms potential alcohol table and you will get a long list to choose from. In fact, the hydrometer that I use came packaged with instructions for its use along with a potential alcohol table and instructions for making temperature corrections to specific gravity readings.
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