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I previously posted about a cider that kept bubbling. Since then, the cider stopped bubbling. I checked the current gravity, and wonder if I have a stuck fermentation because the specific gravity has not changed for five days..

OG was 13.5°Brix on a properly calibrated refractometer. The current gravity is 5.6°Bx, and has been there for five days. The cider is apple juice concentrate diluted to the OG, and pitched with 6 g of properly rehydrated Mangrove Jack M44 yeast. I did not use any yeast nutrient. I understand the FG should end up at 0°Bx.

The cider has been fermenting since Nov. 19. Original fermentation temp in the cellar was 66-67°F for 3 weeks. It naturally dropped to 63°F. I brought it upstairs a week ago, and it is at 70°F.

Should I just expect the cider to take a long time, and exhibit more patience? Or does more need to be done? Rock the carboy to rouse the yeast? Increase the temp more? Move if back to the cellar.

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You say properly calibrated refractomer, but is that a corrected reading to account for the alcohol content? As soon as there is any alcohol in a solution the light is refracted differently so refractomers no longer show a true reading, You can use online refractomer calculators to calculate the corrected reading based on your OG and current reading. –  Anigel Jan 7 at 7:51
    
The calculator here: northernbrewer.com/refractometer-calculator indicates that a starting brix of 13.5 and a current bris of 5.6 indicates a current gravity of 1.002 which is about right for a fully fermented cider. –  Tobias Patton Jan 7 at 15:06
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up vote 1 down vote accepted

My question is answered in the comments. I failed to compensate for the alcohol on the final refractometer reading. The answer is that the cider is done fermenting, having finished at around FG = 1.002.

(For some reason I was mentally confusing wort correction factor that applies to beer but not fruit juices, as researched by Sean Terrill, with correction for the SG of alcohol. Allow me to say "d'oh!" for my rookie mistake, especially because I believe I recently gave an answer about alcohol correction on this forum.)

Note: I am not sure what the etiquette is here, seeing as forum partipants solved my problem in the comments (vote to close, or answer my own), so I am just going to answer my own question.

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