Accurate measurement of alcohol content in mash
Using a hydrometer to measure alcohol strength in mash will not produce entirely correct results. Instead, a special high quality alcoholmeter can be used. Alcoholmeters can't be used in mash directly since any residue in the mash will affect the behaviour on the alcoholmeter. The mash needs to be distilled, for example with the EasyStill. This page contains instruction how to build a simple but effective pot-still suitable for this need, and how to measure the strength in mash.
Short description on the procedure
1. Measure 250 ml of mash in a test jar
2. Pour the mash into a pot-still and distil 200 ml.
3. cool down the distillate to 20 C, measure the strength.
First of all, a pot-still is necessary. Any small pot-still will do, since only a simple distillation is necessary. How to build a simple pot-still can be found here. The mash needs to be stripped of all alcohol, it is therefore necessary to get 200 ml distillate from the 250 ml mash to make sure that all alcohol is stripped from the mash.
Measure 250 ml of mash in a test jar and pour it into the still. If a glass boiler is used it is necessary to add boiling stones to prevent flash-boiling. About anything will do that has a rough surface. Raschigrings, coins, gravel and so on. Not much is necessary, just a few raschigrings for instance.
Make sure the still is well mounted so I can't tilt while distilling. Turn on cooling water for the condenser and turn on heat. It doesn't matter how fast the apparatus is run as long as no foam is getting into the condenser and that the condenser can handle all heat, the distillate should come out cold to prevent any loss of alcohol to the air.
It is easiest to distil directly to a clean test jar to be able to see how much distillate is being removed.
After the distillation is complete, pour extra tap water into the test jar to get back to the original 250 ml. The distillate now has the same alcohol strength as the mash did.
An alcoholmeter graduated from 0 - 30 % is used to measure strength. Since it is calibrated at 20 C degrees it is necessary to either cool or heat the distillate to 20 C. Use a thermometer to check the temperature in the distillate. Cool/heat the test jar under running water to get the right temperature. It is important to mix the distillate well so the temperature in the distillate is even, otherwise cold distillate will have a tendency get stuck into the bottom of the jar . Do that by putting your palm over the top of the jar and turn it up side down and than back. Check temperature again.
Put the alcoholmeter into the jar and read the strength.
Temperature correction script
It's best to cool down the distillate to 20°C And measure the alcohol strength to get most accurate data.
But as an alternative it's possible to use this conversion tool, that temperature corrects the value showed on the alcoholmeter.