Misreading between hydrometer and refractometer

[kenpotf]

All,

I've got a beer in the fermenter that BS says it should be complete around 1.017. The estimated original was 1.072, but I hit 1.062 (the style is within 10 points I believe for a Porter). So, in my notes, I wrote I had 1.062. I don't remember that day very well

Okay, I did a reading with a hydrometer last Thursday and it read 1.022. I had zero krausen, so I figured it would be done but left it. I measured on Friday night with a refractometer that gave me 10 brix. I measured this morning, and it's still sitting at 10 brix. The problem that I have is the converters online show that 10 brix is 1.040 which means I only went down 18 points. If I do another hydrometer reading today, should I call it done if I still get a 1.022 reading? Or should I try to warm the fermenter up or even repitch?

And does anyone know why I would have a discrepancy that large between the hydrometer and refractometer? I understand that the refractometers are better pre-fermentation, but I could've sworn the calculators were pretty accurate...

Thanks!

 

[doug293cz]

Refractometers measure index of refraction of solutions. Since both sugar solutions and ethyl alcohol solutions have higher indicies of refraction than water, refractometers do not read correctly for mixed solutions of sugar and alcohol. (Well they do read index of refraction correctly, but the index of refraction is not simply related to the alcohol or sugar content as it is for unfermented wort.)

It is possible to get an estimate of sp gr of a mixed sugar/alcohol solution, if you know the sp gr of the original wort. Probably the best calculator to use is the one by Sean Terrill: http://seanterrill.com/2012/01/06/refractometer-calculator/. Sean has done a significant amount of correlation between refractometer and hydrometer readings on mixed sugar/alcohol solutions.

Brew on

 

[kenpotf]

Thanks. I played around with that site, and according to it my fg should be around 1.020. I called it at 1.025 and put the vanilla bean in there instead of repitching.

Thanks!

 

[Pappers_]

Using calculators to predict your FG isn't very valuable, in my opinion. There are many variables involved, specific to your process and setup, and the FG will be whatever it is, regardless of the prediction. If a batch ends up too low or too high, you can make adjustments for your next batch, but for the batch you are currently doing, you just need to let the yeast determine what your FG will be.

 

[Demus]

Did you calibrate ur refract with distilled water first? It's amazing how easily they seem to drift off. I do mine before each use....


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