The alcohol concentration of the distillate is determined by measuring their densities using a special alcohol hydrometer also known as an alcoholmeter, usually calibrated at 20 ºC with readings in % v/v.
The scientific formula to calculate this density is:
Density = ro; Weight = m; Volume = V
ro = m / V
Alcohol being less dense than water means that the decrease in density, relative to water, will directly correlate to the volume of alcohol present. If the alcohol solution is greater or less than 20 ºC, the density will be less or greater than the true value. The true alcohol concentration at temperatures other than 20 ºC can be read on a correction table chart, using the temperature and alcohol concentration range.
The distillation and hydrometry method of determining alcohol concentration in distillate is one of the cheapest and simplest to perform with the least chance of errors being introduced.
When using the alcoholmeter, distiller should record the reading results (percentage of alcohol in the distillate) for future reference. These alcoholmeter readings should always be considered at the bottom of the meniscus (point A).
In order to use an alcoholmeter the distiller must decide on one of two methods:
* Use a copper parrot spout, which is attached to the existing tube of the condensing recipient. This spout is made to hold an alcoholmeter and provides distiller with alcohol percentage readings with relative ease.
* Use a test jar which must be cleaned with warm water and dried before use. Pour the distillate into the test jar up to 5 cm (2") away from the rim. Close the test jar with a clean plastic film and with the palm of the hand, shake 10 times! Now dip the alcoholmeter slowly into the liquid until it floats freely. The hydrometer has to be free of bubbles! The reading is taken at the level of the liquid surface. Record the temperature of the liquid. Take care that the temperature of room, liquid and instrument is the same. Store test jar, liquid, instrument about 4 hours in the same room you test!
Distillers should always opt to use an alcoholmeter along with a thermometer which is soldered on the vapour chamber area of the still. With the assistance of these two instruments distiller will be able to collect information on the type of alcohol which is being produced and will know the correct cut off points as specified in the basic distillation rules, which should always be respected.