Wyeast 1968 Fermentation Measured with Refractometer

[Cburke501]

This is the second brew I've done with my new refractometer. The OG measured 12 Plato ( or Brix?), for a OG of 1.048 according to the refractbeer spreadsheet. I checked again after 1 day, and got 1.030, again according to the spreadsheet. Today, the third day after fermentation began, I measured 1.008 according to the spreadsheet with my refractometer. Is this possible?

I intentionally mashed low (148) because I have read about attenuation issues with the 1968 ESB yeast. I did make a starter, but could it possibly have fermented down that much? According to BrewMate, thats around 85% attenuation!

Does anyone else use the refractometer/spreadsheet combo during fermentation? Should I try a hydrometer reading at some point to see where that reads? If the yeast attenuated that much, I don't mind having a light ESB. And I also want to re-use this cake for a Barleywine anyway, so maybe it will work out. I just want to make sure the method of measurement is accurate and makes sense.

 

[Randar]

Once alcohol is being produced, the reading needs to be corrected. There is a "standard" conversion method and several calculators out there on the interwebz to help you correct refractometer readings.

Search for refractometer correction calculator and you should be able to find "for fermenting wort/beer" and "for finished beer"

edit: should have read more carefully? I don't know what the refractbeer spreadsheet is, but I'd guess it's trying to do the conversion for you? You're also swapping between SG and Brix/Plato pretty wildly. If you want help, put all your measurements in Plato out there and then what you're getting when converting to SG.

 

[skyebrewing]

When in doubt, pull out your hydrometer and compare when things that make you question come up

 

[Beernip]

I've seen posts of people reporting up to 88% attenuation with the 1968 yeast so is not beyond reason. Check the hydro though to be sure.

 

[Cburke501]

Thanks for the replies. Yes, the spreadsheet I'm using is from morebeer.com, and does this conversion. So, to keep the units the same, I started at 12 Plato OG, and am now reading 5.7. Using the spreadsheet to correct that number, gives me a SG of 2.1 Plato.

This afternoon I'll probably take out the hydrometer, just to check. This just makes me wonder if its worth using the refractometer to measure gravity through fermentation if the correction for alcohol isn't very accurate.

 

[Randar]

Also, I have found for most of my beers that the approximations used result in about 1-2 points drier than what I actually finish... as measured with a calibrated hydro and refrac.