Refractometer confusion

[Brewskey]

I just finished fermenting my first all grain batch, just a simple APA nothing fancy. OG according to my ATC refractometer was 1.050, a little shy of my target gravity but still okay. Fermentation was business as usual it seems and there is definitely alcohol in the beer. But, when I take a refractometer reading I come up with 5 brix/ 1.019SG, when I put this into one of those refractometer ABV calculators I come up with 1.001 FG or 6.6ABV. Have you ever seen a beer finish so low in gravity?

Beersmith called for a mash temp of 148, I think I was actually at 147. I understand that lower temps means more fermentable sugars, is that what is causing this.

Btw...hydrometer reading was 1.006FG which would be 5.78% ABV... hope I didn't confuse anyone.

Thanks!

 

[Epimetheus]

You have found refractometers are convenient for getting close but to get dead-on accuracy you need a hydrometer. It is good you used a calculator rather than a dual Brix-SG recticle. Those things are always way off at higher gravities.

Refractometers are not so accurate at very low gravities near or below 1.000. The alcohol and sugars drive it down and up, respectively. 1.001 vs. 1.005 - four parts in 1000. I do not think that is poor accuracy. I accept some inaccuracy for the convenience of a refractometer.

The first few times I measured both with a Brix refractometer and a hydrometer and compared them. The calculated sg was close enough for me. If I was getting into competition and needed more accuracy I would use the hydrometer, especially for the FG.