Can the final gravity be multiplied by the ratio of beer to water?

If one ends-up with, say, half as much beer as needed to float the hydrometer, is dilution a viable way to get a measurement?

For instance, if one carefully measured the volume of available beer for the sample, mixed that beer with the same volume of water, then floated the hydrometer and took a reading, could that result be multiplied by 2 to get a valid gravity of the undiluted beer?

Topic final-gravity hydrometer homebrew

Category Mac

1
answered at

Yes. Specific gravity is calculated on relative densities (densitybeer / densitywater in the case of brewing). If you double the volume of the beer as you describe by diluting it with water, then the density will be half (roughly, not accounting for intermolecular interactions). (Dbeer / 2)/ Dwater = (Dbeer / Dwater) /2, so multiplying by 2 would restore the actual original sg of the brew. Keep in mind that this is not exact as there is an inherent error in using the hydrometer (very temperature sensitive).

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