Thought I'd Share some Serious Geekery

[Nosybear]

Am I the only one who caught NB takes samples with a refractometer? My understanding is they don't provide accurate readings once alcohol has been produced and is part of the sample. I discovered this when trying to use it post fermentation and couldn't understand the readings. Pretty cool experiment though Nosy!

Once the fermentation is done, I'll post my latest profile, a Dampfbier (think Erdinger Weissbier in terms of color and flavor, but a 100% barley malt). I added a line for the actual "measured" refractometer readings. There's a correction equation that'll keep the results within measurement error when converting, published in Zymurgy magazine I believe last July. I use that to correct. Since my refractometer reads in degrees of SG and my hydrometer in two degree increments, the refractometer, corrected, is actually more accurate than the hydrometer.

Think about it this way: Most measurement devices are "corrected" some way. A scale doesn't directly read the weight, it reads how much a spring is displaced or today, the amount of strain a gauge reads. A pH meter measures electrical voltage then converts that into pH readings. A modern electronic thermometer reads the change in resistance in a sample. The refractometer itself measures the index of refraction of the fluid, not the specific gravity. It's no different, I'm just doing the correction calculations externally.

 

[Hogarthe]

Am I the only one who caught NB takes samples with a refractometer? My understanding is they don't provide accurate readings once alcohol has been produced and is part of the sample. I discovered this when trying to use it post fermentation and couldn't understand the readings. Pretty cool experiment though Nosy!

You can use a refractometer correction calculation to read it after fermentation. May not be 100% accurate but should be close. Without the correction the reading is gibberish.

 

[Hawkbox]

I use refractometer for the post boil reading and then take a hydrometer reading when I'm kegging. mostly because i dont want to deal with math.

 

[Nosybear]

I use refractometer for the post boil reading and then take a hydrometer reading when I'm kegging. mostly because i dont want to deal with math.

Spreadsheet. Only way to fly and you get a pretty graph!

 

[OkanaganMike]

Thanks for the explanation Nosybear, that makes more sense to me now

 

[Nosybear]

As promised, the fermentation curve for my Dampfbier - think an all-barley grist fermented with Weizen yeast:

The "green" line is the actual measured gravity with the refractometer, the red line is the corrected gravity. The blue line is the predicted FG (1.011), it ended up at 1.010.