A hydrometer is an instrument used to determine specific gravity. ... Liquids lighter than water are scaled below 1.000 specific gravity, and liquids heavier than water are scaled above 1.000 specific gravity.

Is a hydrometer necessary?

You don't absolutely need a hydrometer, but it's a great tool to have for brewing. By using it, you can: Accurately determine how much sugar is in your must or wort (the mixture that you start your fermentation with) Check to see if your brew is still fermenting, or if it has stopped or stalled.

Why is a hydrometer more accurate?

Precision - as long as temp is about 70f the hydrometer will be more reliable since it is based on a large sample and uses density. Accuracy - the refractometer has to be recalibrated, using a hydrometer or by making a known solution with a scale. Also, a wort correction factor should be used.