Fermentation Basics
How to Use a Hydrometer
A step-by-step guide to taking repeatable gravity readings with a brewing hydrometer.
Prepare a clean sample
Rinse and sanitize the sampler and test jar. Draw enough liquid for the hydrometer to float freely, and avoid taking a sample from a layer of fruit, foam, or sediment.
If the sample contains visible gas, degas it gently in a safe, clean way before measuring. Bubbles adhering to the instrument can lift it and create a falsely high reading.
Read the scale correctly
Lower the hydrometer carefully into the sample and give it a gentle spin. Read the meniscus at eye level according to the instrument maker’s instructions.
Note sample temperature and compare it with the hydrometer calibration temperature. Apply the manufacturer’s correction when required, and record the corrected reading and method.
Clean up and interpret
Do not pour the sample back into the fermenter. Clean the instrument and equipment promptly, then compare the reading with earlier measurements.
One reading is a snapshot. Repeated readings several days apart help establish whether fermentation has reached a stable endpoint.