Correct refractometer Brix readings taken after fermentation has begun. Alcohol skews refractometer readings, making them unreliable without correction.
A refractometer measures the refractive index of a liquid, which correlates to sugar concentration (in Brix). However, once fermentation begins, the presence of alcohol changes the refractive index, making raw Brix readings inaccurate.
This calculator applies a cubic polynomial correction formula using both the original and final Brix readings to determine the true final gravity:
Tip: Always calibrate your refractometer with distilled water before use. The standard wort correction factor of 1.04 works for most beers; adjust only if you have specifically calibrated your instrument.