I have an IPA that I've brewed in five gallon batches before. OG at 1.065 and FG at 1.010. Those were hydrometer readings.

I scaled it down for a one gallon batch, and pitched half a packet of yeast (Safale US-05) instead of a full packet. My OG was 1.060 using a refractometer, but my FG is reading 1.041 after 2.5 weeks of fermentation.

Is something throwing the refractometer off? I haven't had this issue before.

Maybe I under-pitched? But half a packet of yeast for a one gallon should be plenty, right?


  • Is your fermentation completed? At least 3 days in a row with stable gravity? Is the fermentation temperature the same?
    – Philippe
    Jul 4, 2019 at 18:30
  • I didn't check that :/ Same fermentation temp throughout the 2.5 weeks.
    – mstrom
    Jul 4, 2019 at 19:03

1 Answer 1


If you're measuring FG with a refrac, you need to compensate for alcohol. Alcohol in solution will increase the apparent gravity in a refrac. For this exact reason, I never measure gravity with a refrac after I've pitched yeast.


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